Presented by Andrea Altmann
Vascular endothelial cell growth factor (VEGF) enables the precursors of blood vessels to form endothelial tubes. Survival of these tubes is dependent on an alpha v beta 3 integrin that may be used in gene delivery strategies. Endothelial tubes connect a network of capillaries that are remolded into arteries and veins through a process known as angiogenesis. Angiogenesis is important in tumor growth because it allows tumors to have a direct blood supply. However, the process of angiogenesis can be surpressed by the Ras-Raf-MEK-ERK pathway which contains a Raf gene which blocks endothelial signaling and angiogenesis.
This paper examines the role of alpha v beta 3 when coupled to a cationic nanoparticle to see if alpha v beta 3-NP could deliver genes to an angiogenic tumor associated blood vessel. To do this alpha v beta 3-NP was coupled to both a green fluorescence protein (GFP) and a cDNA encoding mutant Raf gene. It was injected into mice who had M21 and M21-L cancer melanomas. They found that alpha v beta 3 works to deliver genes to angiogenic blood vessels and that tumor regression can be surpressed by this delivery system.
Links related to the paper:
PubMed Abstract of the Article
ScienceDaily News Release - An article describing the paper
Understanding Angiogenesis-endothelial cell activation - An overview of angiogenesis and cancer
Animation of the Ras-Raf-MEK-ERK pathway
Molecular Basis of Angiogenesis - An in depth look at angiogenesis by one of the authors of the paper
Integrin Activation in the Metastasis of Breast Cancer - A look at alpha v beta 3 in breast cancer
Presented by Jon Hodges
Retinoblastoma is an important protein in the regulation of the cell cycle, more specifically, as discussed in this paper, in the transition from the G1 phase to the S phase. It is composed of an A and B domain and actively represses transcription in two ways. The first is by binding to the E2F family of transcription factors and essentially rendering it inactive. Secondly, this Rb-E2F complex can bind with histone deacetylase and in turn to the promoter region of the gene being repressed. Histone deacetlylase (HDAC) aids in transcription repression be removing inhibitory acetyl groups from the amino-terminal end of the histone octamers. This interaction promotes nucleosome formation which in turn inhibits transcription by limiting the access of the transcription factors to the promoter regions of the genes.
Phosphorylation of specific sequences of Rb leads to inhibition of their ability to bind to their protein counterparts. If the T-821 or T-826 sequences on Rb are phosphorylated, they can no longer bind to proteins containing the needed LXCXE sequence which is found in HDAC, for example. Furthermore, if several more of these sequences are phosphorylated then Rb loses its ability to bind to E2F as well as HDAC and consequently loses its ability to repress transcription. This phosphorylation is catalyzed by cyclin-dependent kinases (Cdk) which form complexes with their respective cyclins when they are expressed. The paper discusses the expression of cyclin-D in the G1 phase of the cell cycle and its subsequent binding to Cdk-4 or Cdk-6. This newly formed cyclin-cdk complex actively phosphorylates specific regions of the pocket, or active binding site, of Rb. This disruption in pocket structure, for example, inhibits HDAC from being able to bind and consequently to promote transcriptional repression. The pocket's structure does not have to be altered in this way, however, because these complexes will also phosphorylate the C-terminal end of Rb which will then bind to the pocket instead of HDAC. Various experiments are discussed that support this evidence as well as the significance of these Cdk complexes.
There are many more mechanisms discussed in the paper showing the effects of phosphorylation on Rb's ability to actively repress transcription. The expression of the various cyclins at different points in the cell cycle can lead to an inactive Rb protein and consequently an inability to stop cell growth or repress cell proliferation. This occurs, as mentioned, through the loss of Rb's ability to bind to E2F, the loss of HDAC's ability to bind to the active pocket on Rb, and the binding of the C-terminal region of Rb to the pocket which in turn prevents HDAC's binding. These mechanisms coupled together can cause unchecked cell growth and ultimately cancer.
Links related to the paper:
PubMed Abstract of the Article
Description of Rb as it relates to this paper(includes links).
Phosphorylation - a quick overview of the fundamental process discussed in this paper.
Map of Rb expression versus the Cell Cycle Time Table.
Cyclin/Cdk Overview - Relavent information regarding the catalyst of this research
Presented by Remy De La Peza
This article highlighted the interaction between WISP-1, Akt and p-53 in the formation of cancer. The oncogenic growth factor known as Wnt-1-induced secreted protein 1 (WISP-1) is overexpressed in 84 % of human colon cancers. It is a downstream target gene of the Wnt-1-beta-catenin signaling pathway and is found on human chromosome 8. WISP-1 is a member of the CCN family of growth factors, characterized as a secreted, heparin-binding, cystein rich, extracellular matrix-associated protein.
Some members of the CCN family bind to integrin receptors rather than to receptor tyronsine kinases. This can affect cancer cell invasion and growth by activating downstream targets like Akt (also known as protein kinase B [PKB]), a serine/threonine kinase. When Akt is phosphorylated and activated it promotes cell survival and inhibits apoptosis.
Caspase pathways, as discussed in lecture, are ultimately activated by apoptotic signaling, including the role of cytochrome-c and Apaf-1 in the activation of caspase-9 and procaspase-3. Such targets lie downstream from p53, a tumor suppressor gene which prevents cancer in one of two ways. It either arrests the cell cycle at G1 to repair damaged DNA or it initiates apoptosis when the cell is exposed to a stressor (i.e., DNA damage, oncogene activation, hypoxia, or the loss of normal cell-cell contacts).
The goal of this study was to determine whether WISP-1 promotes tumorigenicity by suppressing p53 regulated apoptosis and if so, to what extent. WISP-1 was found to activate Akt, which inhibits apoptosis via inactivation of caspase-9. It also inhibits apoptosis induced specifically by DNA damage, shown to be generalizable to several cell types. In particular, WISP-1 blocks the activation of caspase-3 and inhibits the release of cytochrome-c. This data, along with the findings that WISP-1 upregulates the anti-apoptotic protein Bcl-XL and is unable to inhibit p53 independent apoptosis, provides support for the fact that WISP-1 does in fact suppress p53 regulated apoptotic pathways and is involved in some cancer formation.
Links related to the paper:
PubMed Abstract of the Article
Improving Cancer Chemotherapy - Recent research at the Rockefeller University on the interaction between p53 and WISP-1 and the advancement of chemotherapy
Summary of Wnt signaling and cancer
Presented by Lindsey Bowman
Beta-catenin is a multifunctional cytoplasmic protein which is implicated in the cadherin cell adhesion complex as well as in transduction of extracellular signals. Cytoplasmic beta-catenin levels are believed to be regulated by the Wnt signal transduction pathway. The Wnt signaling cascade is known to play an important role during embryonic patterning and cell fate determination, depending on the levels of beta-catenin in the cell. The signaling activity of beta-catenin is thought to be regulated by phosphorylation of the N terminus of Glycogen Synthase Kinase 3 Beta (GSK3beta). Wnt signaling inhibits GSK3beta activity, thus blocking degradation of beta-catenin. Unphosphorylated beta-catenin escapes degradation, accumulates in the cell, and enters the nucleus. In the nucleus, beta-catenin interacts with other transcription factors to stimulate expression of target genes.
Studies in recent years have suggested that beta-catenin is a potent oncogene product and its accumulation had been implicated in tumorigenesis. Deregulation of the Wnt signaling pathway results in aberrant accumulation of beta-catenin in the nucleus, often leading to cancer. Constitutively active beta-catenin complexes, and inappropriately activates target genes, which is an early event of carcinogenesis. This increased expression of beta-catenin is usually followed by a later mutational inactivation of the p53 tumor suppresser. The p53 protein plays a key role in cell cycle, control, and apoptosis. A possible relationship between beta-catenin and p53 is suggested by the observation that cancers resulting from abnormal accumulation of beta-catenin also exhibit a high frequency of p53 mutations. This paper takes a closer look at this relationship.
First, the researchers show that excess p53 reduces beta-catenin protein levels and mutant p53 does not act to down-regulate beta-catenin. Thus, a relationship exists between the two. Furthermore, this relationship is more clearly defined as reciprocal in nature. High levels of beta-catenin cause high levels of p53, which in turn cause beta-catenin levels to decrease. Additionally, GSK3beta activity is shown to be necessary for p53 to be active. Wnt signaling causes beta-catenin accumulation by decreasing the ability of GSK3beta to phosphorylate beta-catenin. Finally, researchers show that deregulated beta-catenin activity can lead to p53 inactivation, and ultimately to cancer. Pulling all the results together, a negative feedback loop involving p53 and beta-catenin is proposed. Disruptions in this loop leading to deregulation of beta-catenin may be to blame for the high frequency of p53 inactivation observed in several types of cancer.
Links related to the paper:
PubMed Abstract of the Article
Excess Beta Catenin promotes accumulation of transcriptionally active p53 - a related paper which is made reference to several times
The Wnt Signaling Pathway - a description of the key events involved in the Wnt signaling pathway
Molecular Oncology of the Wnt Signal Transduction Pathway
p53 - a brief overview of the p53 tumor suppressor gene
Biocarta: Charting the Pathways of Life- The Wnt Signaling Pathway - a detailed schematic showing the complexity of the Wnt signaling pathway and the role of Beta-catenin
A comprehensive table summarizing beta-catenin mutations found in various human cancers
Presented by Meg Kelly
Apoptosis occurs in some avian hindbrain premigratory neural crest cells located in rhombomeres 3 and 5 (r3, r5). This process of programmed cell death in these rhombomeres has caused a lack of cell migration from these two areas during the developmental process. The cells from r3 and r5 that do not undergo apoptosis have been shown to migrate with the r4 cells into the second branchial arch. This study was conducted to attempt to determine why this apoptosis occurs, to what extent it occurs, and to discover the effects of manipulations on the rhombomeres 3, 4, and 5.
Ellies first focused on the possible short-term and long-term effects of manipulations on the r3, r4 and r5 including the exchange or replacement of the chick rhombomeres and grafting of foreign rhombomeres such as quail in early chick embryos. These in vivo manipulations were done to attempt to find the cause and reasoning behind apoptosis of r3 and r5 as well as the natural migrations and pathogenic blocks of the cells that survive. The results of these many experiments will be covered in detail in the class presentation.
One way to avoid apoptosis in r3 and r5 is to ablate r4 at an early stage. Not only does this show that interrhombomere interactions do occur, but it also raises the question as to why and how this causes apoptosis to be prevented. It was shown that the r3 and r5 cells do not die in the case of the ablation of r4, but instead attempt to substitute for the cells lost from r4 in the creation of the retroarticular process and the columella, but were not able to compensate completely as those structures were found to be of abnormal size in this experiment. The new migration patterns that were caused by r3 and r5 attempting to adapt to the loss of r4 do not occur on top of or along with the normal migrations patterns of the few apoptosis survivors in a normal embryo. It was discovered that the migration patterns do change with the loss of r4 not only in the amounts but also in the final destinations.
Links related to the paper:
PubMed Abstract of the Article
Physiology Department presentation at the University of Iowa - A description of what rhombomeres are and another experment for background information.
Graham, A. "Even-numbered rhombomeres control the apoptotic elimination of neural crest cells. . . "
MRC Centre for Developmental Neurobiology - The author's department's homepage
"Segmentation and specification in the branchial region of the head: . . . "
Presented by Julia Mills
p53 is a tumor suppressor gene found in mammals that plays a regulatory role in the cell cycle and in apoptosis (programmed cell death) in response to cellular stresses. Increased levels of p53 activity can be seen in cells due to radiation exposure, DNA damage, hypoxia, and oncogene activation. p53 acts as a transcriptional regulator of specific target genes. It contains a sequence specific DNA binding domain, an acidic N-terminal domain associated with transcription activation, and a basic C-terminal domain associated with sequence non-specific binding and tetramerization. The tetrameric structure allows p53 to function in a dominant negative manner, implying that the phenotype of the mutant allele will be dominantly expressed throughout the entire tetrameric structure. The loss of p53 function is commonly seen in tumors occurring during the development of cancers.
To date the gene targets of p53 that regulate the cell cycle and apoptosis are unknown. The goal of the examined research was to locate a homolog to the human p53 gene in Drosophila, then conduct various experiments using Drosophila to identify the conserved gene targets of p53. Previous experiments have noted that ionizing radiation induces the transcription of the reaper (rpr) gene in Drosophila resulting in apoptosis. This observation led the authors of the paper to examine rpr as a possible gene target of Drosophila p53.
The research conducted by the authors of this paper indicate that the Drosophila gene rpr contains an enhancer that responds to radiation; the enhancer contains a binding site for Drosophila p53; and the binding site can mediate transcription as a response to radiation. These observations lead to the conclusion that rpr is in fact a transcriptional target of Drosophila p53. The conservation of Drosophila p53 structure and function will allow for further analysis that may provide information about the function of p53 in human cells.
Links related to the paper:
PubMed Abstract of the Article
The Berkley Drosophila Genome Project.
Hot molec. Base:The p53 tumor supressor - Describes structure, function, involvement in disease and animal models of tumor suppressor p53.
p53 - Biological overview of p53, supplement to Brodsky paper discussing Drosophila p53 homolog.
Umass medical school: Program in gene function and expression - Brodsky website. Gives example of how Drosophila p53 regulates irradiation induced apoptosis.
Genome News Network. - Describes utilization of Drosophila to study biology of human diseases.
Presented by Michaela Haney
UV-B radiation is emitted in sunlight and is responsible for most skin cancers as it causes severe DNA damage. Current depletion of the ozone layer (which serves to protect us from severe amounts of UV-B radiation) is increasing the amount of UV-B light that is reaching the atmosphere. Excessive exposure to this radiation can seriously damage individual cell's DNA as well as weaken and harm a person's immune system. Clearly, because it is often difficult or even impossible to avoid UV-B radiation exposure, this is a public health concern that needs to be addressed.
The gene p53 is found in the epidermis and is a tumor suppressor. Hence, it is a prime interest of researchers. It plays a role in UV-B radiation protection because the protein of p53 responds well to DNA damage. Approximately 50% of all human cancers have a mutated form of the p53 gene. This promising gene induces apoptosis of those cells that become damaged due to UV-B radiation.
A new family of genes, called the p63 family, has just been discovered. Two recently determined homologues of p53, called p63 and p73, belong to this family. This new family shares extensive homology to p53 except that this family is distributed in a tissue-specific fashion in the basal layer of the stratified epithelia (which includes the epidermis.) The most highly expressed p63 isoform is īNp63Ą which doesn't induce apoptosis. Those embryos that possess the mutant form of p63 show severe craniofacial and limb defects that eventually result in death. Those embryos lacking p63 altogether do not have a normal epidermis or any hair follicles. Therefore, p63 is essential to normal epidermal development.
In this study, the response of p63 to UV-B radiation and its role then in the epidermis was observed. It was found that īNp63Ą is down-regulated in response to UV-B. Transgenic mice were then made that showed an overexpression of īNp63Ą in the epidermis. Although these mice did develop a normal epidermis, they showed a decrease in the UV-B-induced apoptosis of damaged cells. Therefore, it was determined that the down-regulation of īNp63Ą (which is part of the p63 family) is essential for normal UV-B-induced apoptosis of those cells damaged by UV-B radiation. Gaining a solid understanding of these genes and their inclination or not to induce apoptosis in damaged cells may help strengthen the fight against skin cancer caused by UV-B radiation.
Links related to the paper:
PubMed Abstract of the Article
Health Effects from Increased Exposure to Ultraviolet-B (UV-B) Radiation due to Stratospheric Ozone
Comparison of the expression of p53, p21, Bax and the induction of apoptosis between patients with b
Skin Cancer: Preventing America's Most Common Cancer This site is just one of many sponsored by the CDC. On this site, there are multiple other links to other sites that all provide interesting information and current information regarding skin cancer.
p73 - A Structural and Functional Homolog of p53 - Antibodies This site (although it looks to be primarily for p73) gives a quick overview of p53, p63, and p73.
Apoptosis This site, sponsored by "Nature," simply offers multiple links that provide more basic and background information on apoptosis and p53 genes.
Dennis R. Roop This is the research home page of the primary author of my paper, Dennis R. Roop.
Presented by Patrick Echolds
As you may recall from lecture, limb development is regulated by interactions between specialized epithelial cells in the apical epidermal ridge (AER) and the underlying mesenchymal cells in the posterior region of the limb bud, called the zone of polarizing activity (ZPA). The developing limb is also shaped by programmed cell death in regions designated as the anterior necrotic zone (ANZ), the posterior necrotic zone (PNZ) and the regions between the digits called the interdigital necrotic zone.
BMPs are a family of proteins that belong to the TGF beta superfamily and are very important in development. They bind to two types of serine threonine kinase receptors, type I (BMPRI) and type II (BMPRII). Various BMP’s are expressed in the undifferentiated mesenchyme and the AER of the developing limb. The serine threonine kinase receptors of BMP also show specific temporal and spatial expression in the developing limbs of the chick and mouse.
Some of the functions of BMP signaling include the following: regulation of the growth and regression of the AER in the chick, specificity of anteroposterior digital identity, mediating interdigital cell death and providing the necessary signals for the proliferation and differentiation of precartilaginous mesenchyme of the phalangeal region in mice. The functions of BMP are antagonized by many proteins, including Noggin, Chordin, Gremlin and follistatin.
The specific proapoptotic role of BMPs is still in question. This study provides in vivo evidence that BMP signaling is necessary for apoptosis in the mouse limb. Udayan Guha et al. used the K14 promoter to express Noggin (the BMP antagonist) in transgenic mice. These mice had soft tissue syndactyly, postaxial polydactyly and decreased apoptosis in the necrotic zones of the developing limb causing incomplete regression of the interdigital tissue and a possible fate change in the posterior necrotic zone region to an extra digit. These abnormalities could then be rescued by creating a double transgenic mouse misexpressing both Noggin and BMP4 under the K14 promoter, showing that the abnormalities are a direct result of inhibiting BMP signals.
Links related to the paper:
PubMed Abstract of the Article
Apoptosis - An overview of the history and new research of Apoptosis
Programmed Cell Death in the Developing Limb Bud - A related article on BMP and Apoptosis in limb development
The WWW Virtual Library: Cell Biology: Apoptosis - A library of info and links on programmed cell death
Programmed cell death in development
Presented by Abby Young
Hepatocyte growth factor-scatter factor (HGF) is a heterodimeric growth factor expressed within the nervous system. Both HGF and its transmembrane receptor, c-Met forms a biologically functioning unit on target cells within the developing hippocampus of the rat. HGF functions by promoting neural induction within the brain. Actin as a chemoattractant, HGF also promotes motor neuron survival by cooperating with ciliary neurotrophic factors in teh spinal motor neurons.
Studied in culture with 18 day embryonic rat hippocampus and three day old postnatal rat hippocampus, HGF has been shown to increase, in a dose dependent manner, the number of neurons which express the calcium binding protein, calbindin d. It was also shown through the study to increase the sprouting of calbindin D-positive neurons, thus suggesting that HGF plays a rold in both neuron growth and maturation.
Links related to the paper:
PubMed Abstract of the Article
C-Met - This site explains some of the background about the c-Met receptor protein.
The role of SF/HGF and c-Met in the development of skeletal muscle This site explains some of the other functions of HGF and c-Met within a developing organism.
Presented by Andy Ringnes
The human synuclein family of proteins includes alpha, beta, and gamma synuclein. Alpha-synuclein is predominantly expressed in the central nervous system but can be measured in low levels throughout the body. It is primarily present in the axonal cytosol of nerve cells and readily binds to vessicles. This suggests that alpha-synuclein functions in nuerotransmission or synaptic organization in addition to playing a role in neuronal plasticity. As early as 1997 there was documented evidence of a mutation in the alpha-synuclein gene in families with Parkinson's disease. Alpha-synuclein has since been shown to be associated with a form of Alzheimer's disease, dementia, multiple systems atrophy, and a form of neurodegeneration. The formation of abnormalities in neurons is linked to abnormal alpha-synuclein aggregation in pathological lesions associated with these diseases.
This paper examines the amino acid sequence of the alpha-synuclein protein in order to determine the cause of the abnormal aggregation. The authors implicate a hydrophobic stretch of 12 amino acid residues as being essential for the protein to function correctly. They found that the beta-synuclein protein which is highly homologous to alpha-synuclein except that it lacks the hydrophobic stretch could not form filaments. In addition, the authors determined that adding a single charged residue into the sequence of interest decreased the rate of alpha-synuclein polymerization. The authors found the 12 amino acid stretch to be resistant to cleavage and that similar synthetic peptides self-polymerize. These synthetic peptides could also promote fibrilization of fulllength alpha-synuclein in vitro.
Links related to the paper:
PubMed Abstract of the Article
University of Pennsylvania Health System - Another paper by Giasson describing a-Synuclein Dysfunction and Aberrant Aggregates
Society for Neuroscience - Alpha-synuclein involvement in Parkinson’s Disease
Alpha Synuclein and Parkinson’s Disease in Humans - Description of the alpha synuclein gene. Includes links to figures.
Mayo Medical Research - Fuction of the alpha-synuclein molecule.
Presented by Kristina Angelo
Sympathetic neurons are part of the peripheral nervous system, which is involved in the flight or flight response, and includes a variety of factors to ensure specific cell signaling to target cells. Nerve Growth Factor, NGF, is a neurotrophic factor that is required for the rescue and survival of post-mitotic sympathetic neurons. It is made by the targets of sympathetic neurons, namely, the ear, pineal gland, blood vessels, and submandibular gland and is transported from axon terminals. In this study, the neurotrophic factor NT-3 was tested to determine its role when associated with and compared to NGF in sympathetic neuron survival. This was done by assessing sympathetic neuron development through different periods of precursor growth by using mice with an NT-3 mutation. NT-3’s role in the survival of post-mitotic neurons is thought to parallel that of NGF. Both neurotrophins are associated with Trk receptors which aid neurotrophins in survival promotion.
In this study, wild type mice with no NT-3 or NGF mutation [NT-3 (+/+); NGF(+/+)] and NT-3 deficient mice NT-3 (-/-)were used to determine the dual roles of NGF and NT-3 in cell differentiation during periods of development. During development of the wild type and the mutant, the time of neuron loss is very similar, although the NT-3 deficient mice neuron loss was less severe. By embryonic development day E15.5, neurogenesis was almost completed. In the mice lacking NT-3, no developmental abnormalities or changes in cell count of neurons occurred in the precursor neurons (those before E17.5), suggesting that NT-3 is not effective until later stages. At embryonic day E17.5, the neuron number differentiated between the wild type mice and the NT-3 (-/-) mice, indicating the importance of neurotrophic factors in sympathetic post-mitotic cells, but not precursors. After E17.5, neuron apoptosis increases in the NT-3 mutant mice. Like NT-3, NGF also leads to neuronal loss in stages after E17.5, although the number of neuron loss is more severe.
In this study, the second question addressed was if and how NT-3 promoted neuron survival. In compound mutant NT-3 mice [NT-3(-/+);NGF(-/-)] and [NT-3(+/-); NGF(-/-)] mice, neuronal losses after E17.5 were shown to not be significant. Neuron loss is not significant because NT-3 is still expressed by one allele in blood vessels and target tissues, leading to some survival of sympathetic neurons. Only axon growth is disrupted by the low concentration of NT-3, indicating the necessity for NT-3 in target innervation. Therefore, in late embryogenesis, E17.5, when axon growth is optimal, the number of neurons decreases due to lack of NT-3.
There is a “dual dependency” on NGF and NT-3 to promote sympathetic neuron survival. Through the activation of the TrkA receptor in late neurogenesis, these neurotrophins are able to mediate cell survival of post-mitotic neurons. NT-3 promotes the survival of sympathetic post-mitotic neurons with NGF, although only for a certain time in embryogenesis. The potential for NT-3 to aid in post-natal sympathetic development remains under investigation.
Links related to the paper:
PubMed Abstract of the Article
Dictionary of Cell and Molecular Biology - Definition of Neurotrophin 3 and links to other definitions including other neurotrophins and NGF
Cornell Medical College Research - Discussion of the role of neurotrophins at different stages of neuron synthesis
Scripps Research Institute: Molecular Mechanisms
Story Landis Neural Development Section, NINDS - Story Landis' Lab website with research interests and publications
PIBS Faculty at UCSF; Louis Reichard - Louis Reichardt's Lab; Synapse formation in neural development
PubMed related article abstract - Endogenous Nerve Growth Factor and Neurotrophin-3 Act Simultaneously to Ensure the Survival of Postnatal Sympathetic Neurons in Vivo.
Presented by Michelle Terrell
Huntington's Disease is a neurodegenerative genetic disorder. It is caused by a mutation in the IT15, or huntingtin, gene, which encodes the huntingtin protein. This mutation consists of an expansion of a CAG repeat region. Because CAG is the codon for glutamine (Glu), this leads to an expansion of the Glu repeat region in the protein known as the polyglutamine region. The exact mechanism of pathogenesis is not known for this disease. There are many research projects currently under way aimed at discovering the function of the huntingtin protein in both its wild-type and mutant form.
This paper addresses evidence that the wild-type huntingtin protein is involved in up-regulation of brain-derived neurotrophic factor (BDNF). The researchers found that huntingtin modulates the transcription of the gene encoding BDNF, and that it does so specifically in neurons. Wild-type huntingtin modulates this gene positively while the mutant protein down-regulates this gene. They do this by interacting with the activity of the promoter. These findings were observed both in vitro and in vivo and suggest a possibility for a start point for the cascade of neuron death seen in Huntington's Disease.
This evidence of the mechanism of pathogenesis allows for a better understanding of the disease. If the functions of the wild-type and mutant proteins can be ascertained, possible treatments for this disease could be determined. For instance, increasing levels of cortical BDNF could prevent the cascade of neuron death thereby preventing the disease. Also, in knowing the function of huntingtin, it is possible that a drug that mimics this function in vivo can be derived.
Links related to the paper:
PubMed Abstract of the Article
Huntington's Disease Society of America
Article about the study being presented
Information about Neurotrophins
Presented by Arlene Bartolome
Neural ectoderm patterning in Xenopus laevis involves initiation by posteriorizing signals, which are given by the "organizer," and induce the formation of posterior neural ectoderm rather than anterior neural ectoderm. Three posteriorizing signals include retinoic acid (RA), fibroblast growth factors (Fgfs), and Wnt (wingless) signaling proetins. The role and interaction of these three families of proteins, however, is not fully understood. This paper investigated cyp26, a protein expressed in anterior neural ectoderm, and focused on the interaction between cyp26 and these three signals on posteriorizing neural ectoderm in zebrafish.
The cyp26 gene encodes an enzyme that degrades Retinoic Acid. This suppression of RA signaling is needed to prevent the activation of posterior gene expression. RA is also necessary and sufficient for the activation of some posterior-specific genes. The ability of Fgfs and Wnts to induce expression of the posterior genes is dependent on the presence of RA.
From the experiments, the researchers show that anterior gene and posterior gene expression are highly regulated and never overlap. Posteriorization of the neural ectoderm can be divided into two different steps. First, Fgf and/or Wnt signals suppress the expression of anterior genes, such as cyp26. The second step involves the activation of posterior gene expression, which is RA-dependent. As a widening of the cyp26-negative area occurs, RA can accumulate and is then able to activate posterior genes, such as hoxb1b. Therefore, the cyp26 gene plays a distinct role in regulating anterior-posterior patterning of the neural ectoderm.
Links related to the paper:
PubMed Abstract of the Article
Posteriorization by FGF, Wnt, and retinoic acid is required for neural crest induction
Differential expression of chicken CYP26 in response to retinoic acid
Interactive fly, Drosophila - conserved pathway for FGF signaling, and Wnt, studied during retinoic acid-mediated differentiation
Molecular Neurobiology of Development
Presented by Veronica Rojas
It is known that lin-11 is involved in the pathways for the development of the vulval-uterine connection. In fact, lin-11 mutants do not produce a functional egg-laying system due to defects of the vulva and utse cells. There are two pathways involved in the wild-type development of this system; the LIN-12/Notch signaling pathway and the LIN-17-mediated Wnt signaling. In this research paper scientists looked at the possible regulatory elements that may be involved in the activation of lin-11 during development of the egg-laying system.
So researchers asked, "How is the expression of lin-11 regulated and by which pathway(s)? They preformed many experiments to find out as much as possible about lin-11. They looked at the upstream region of the lin-11 gene and performed experiments to find any tissue-specific elements. Several elements were found to be involved in either uterine pi cell development or in the vulval cell lines. They then used different sequences of the various upstream DNA lin-11 regulatory sequences to see if they could rescue egg-laying defective mutants.
Besides identifying the various ways that lin-11 is involved in the development of the vulval-uterine connection, researchers wanted to know how it is regulated. Experiments were performed to find any transcription factors that could possibly be involved. One of the techniques utilized in these experiments was RNAi soaking. The vulval expression of lin-11 is believed to be regulated by LIN-17, which is part of the Wnt pathway. They also located several sites at which they believe that LAG-1 controls transcription of the uterine pi cells(part of the LIN-12/Notch pathway). This new information gives us a clearer picture of the interaction between pathways to get the wild-type egg-laying system with the appropriate uterine to vulval connection.
Links related to the paper:
PubMed Abstract of the Article
BCM-Developmental Biology - Discusses the LIN-12/Notch pathway in vulval development in C.elegans
An Analysis of Cell Signaling Events Required for Cell Fate Specification During C.elegans Vulval De
The Structure of the Developing Uterus in the L4
Asymmetric Cell Division - Site discusses the importance of multiple signanling pathways that lead to differentiation and development of different structures in C.elegans.
RNAi Describes how the technique of RNAi is utilized and how it is done.
Presented by Barbra Calantas
Homeotic gene complexes have been found in Drosophila embryo developement to contro anterior/posterior patterning and segmental identity. The two homeotic gene complexes found in Drosophila ar Antennapedia and Bithorax; Antennapedia is located anteriorly with five homeobox genes, and Bithorax, the homeotic complex discussed in this paper, is composed of 3 homeoboxes. These three genes which encoded the posterior portion of the embryo, found anterior to posteriorly, are ultrabithorax (Ubx), abdominal-A (abd-A), and abdominal-B (abd-B). These genes combined with the hedgehog (hh) signaling pathway, are studied in this paper to describe their affect on heart tube patterning and segment identification in Drosophila. Its heart is a simple, linear cardiac tube divided into two parts, with an aorta as the anterior section and the "heart" as the posterior section. The Bithorax Complex (BXC) works with hh and a transcription factor seven-up (svp) for the pattern segmentation of the heart.
The results found in this paper are significant because they lead a way to examine the diversification of cardioblast cells (precursors of cardiac tube cells) to more clearly understand the genetic precursors of organogenesis. This paper also supports the Bithorax Complex genes' role in the segmentation of the cardiac tube as the identity definer for posterior patterning, as well as the important role of hedgehog as an inductive signaling pathway. The BXC is shown to provide axial information anterior to posterior, specifically with the genes Ubx and abd-A. Segmental information is given by the induction of the hh pathway, which turns on expression of svp transcription factor, to differentiate cardiomyocytes within segements in the tube. What's also significant about these two pathways is they work in parellel routes, independant of each other. Another point discusses the expression of BXC homeotic genes found to be regionalized in the cardiac tube, showing evidence for these genes to control the patterning of the heart along the anterior to posterior axis; Ubx and abd-A are specifically found to display a "regionalized expression profile."
The Main Points of this Article discuss several topics. The first is the differentiation of cells in the cardiac tube during embryogenesis, describing the basic morphology of the cardiomyocytes to analyze organogenesis. In the examination of segmental identity, the function of svp as the transcription factor required for the differentiation of cardiomyocytes into ostiae, the openings for hemolymph to flow into, is examined by showing work done with svp mutants and changes in morphology of segments. Finally, the expression of svp for the diversification of cardioblasts requires the hh signaling pathway.
Links related to the paper:
PubMed Abstract of the Article
PubMed Abstract of related primary literature - This Abstract describes a similar topic of the regulation of a gene Ultrabithorax, within the HOM-C of the Bithorax Complex.
The Hox gene abdominal-A specifies heart cell fate in the Drosophila dorsal vessel
Segmentation and positioning of the Drosophila heart is mutually dependant on positional and regiona
The Drosophila heart - pictures of a dorsal view of the Drosophila heart