Spring 97 Bio 580 Symposium

Spring '97 Bio 580 Symposium

Topics & Abstracts

8 min talks to be given May 12, 1997

Efrat Ron | Email: efrat@student.umass.edu Dorsal-ventral polarization of Drosophila melanogaster

ABSTRACT

Dorsal-ventral polarization in Drosophila melangaster is determined through the action of many genes and proteins that are part of the maternal effect genes. The maternal effect genes are 12 loci that include snake, spätzle, pipe, nudel, gastrulation defective, easter, Toll, torso, cactus, tube, pelle, and windbeutel. The gene that has the most effect on dorsal-ventral polarization of the embryo is Toll. Toll thought to be the leader, or at least the first gene that is turned on in the cascade of genes that will eventually determine the dorsal and ventral poles of Drosophila melangaster. After the Toll gene is turned on, a morphogenic concentration gradient is initiated by the protein concentration of Toll; it switches on the dorsal gene, which helps to determine the location of the ventral gradient. The gradient is predominantly found to be localized in the ventral most area of the embryo and the embryo develops according to a ventralized pattern. This morphogenic gradient turns on the genes twist and snail, which aid in the determination of the dorsal-ventral poles.

Mark Livingstone | Email: guy@student.umass.edu Dorsal-Ventral Patterning of Photoreceptors in the Developing Zebrafish Retina

ABSTRACT

Recently, the zebrafish has become one of the commonly studied organisms by developmental biologists. Many factors have contributed to make this common aquarium fish an easily studied model for vertebrate development. One system commonly studied in this teleost is the vertebrate eye. The zebrafish, however, cannot be considered to be a representative of all vertebrates in this respect, since vision in an aquatic environment is much different than in a terrestrial one. Light in an aquatic system primarily comes from above, illuminating only the tops of objects.
Such an environment necessitates special photoreceptor patterning in the retina. The regions of the zebrafish retina that collect light from the bottoms of objects need more rods, which allow monochrome vision in low light, while the retinal regions that visualize the tops can contain more cones, which allow color vision at higher light levels. Retinoic acid has been suggested to be the signalling molecule that controls which type of photoreceptor (rod or cone) retinal progenitor cells will become. Possible mechanisms for the patterning of photoreceptors via the action of retinoic acid are discussed together with other aspects of vision development in the zebrafish.

Dena Janigian | Email: dmjanigi@mhc.mtholyoke.edu

Genetic mechanisms of programmed cell death
in Caenorhabditis elegans

ABSTRACT

Programmed cell death is a tightly regulated program in which dying cells play active roles in promoting their own death and subsequent removal from the organism. Programmed cell death plays key roles in development, homeostasis, and diseases such as cancer or neurogenitive nerve disorders. The nematode Caenorhabditis elegans undergoes natural programmed cell death in roughly one sixth of its somatic cells during development. While all cells are thought to contain the basic machinery for thei cell-suicide program, programmed cell death is strictly regulated by a wide array of different intracellular and extracellular signals. Fourteen genes have been discovered that operate in the C. elegans cell death pathway. Isolation of these genes and gene products has led to the subsequent identification of genes in other organisms that have similar structures and functions. Discovery of these genetic homnologs reveals that at least some components of the cell death program have been conserved evolutionarily among nematodes, insects, and mammals, suggesting a common program for programmed cell death that is of ancient origin. Understanding and control of programmed cell death mechanisms thus holds many important consequences for therapeutic intervention in humans.

Sarita C. DelGado

The roles of temperature, steroids, and steroidogenic enzyme activity in turtles exhibiting temperature-dependent sex determination

ABSTRACT

In many turtles such as Emys orbicularis and the red-eared slider turtle, Trachemys scripta, the incubation temperature of the egg determines the gonadal sex of the offspring. This process known as temperature-dependent sex determination (TSD) involves nonaromatizable androgens in male sex determination and estrogens and aromatizable androgens in female sex determination. Studies have demonstrated that the administration of exogenous estradiol and its agonists to eggs incubating at a male- producing temperature can overcome the effect of temperature and result in all-female offspring. However, the administration of exogenous dihydrotestosterone (DHT) or testosterone to eggs incubating at an all-female temperature will have no discernible effect. Studies have further indicated that the administration of DHT will cause male sex determination only if administered at intermediate incubation temperatures, whereas administration of testosterone to eggs incubating at all male-producing and male-biased intermediate temperatures results in a significant number of female offspring. This effect is presumably due to the pivotal role played in TSD by the enzyme aromatase, which produces estrogens from androgens. Since testosterone serves as the precursor to both DHT and oestradiol (OE2), which are metabolized by reductase and aromatse respectively, experiments utilizing reductase and aromatase inhibitors determined whether such inhibitors would overcome the effect of incubation temperature. The results indicate that aromatase is involved in determination of females while the regulation of reductase gene(s) is critical to a testis-determining cascade. Furthermore, the administration of either reductase or aromatase inhibitors can reverse TSD and such inhibitors act on the enzymes themselves, rather than through the steroid receptors. Overall, strong evidence exists suggesting that sex steroids, specifically estrogens, mediate gonadal differentiation in TSD species.

Steve O. Kwon | Email: skwon@oitunix.oit.umass.edu Hh, Wg and Dpp Interactions in the Cascade of Drosophila Leg Development

ABSTRACT

Hedgehog (hh), wingless (wg) and decapentaplegic (dpp) are three genes that play a vital role in the leg development of Drosophila melanogaster. Leg development is signaled by a cascade network of genes of which hh, wg and dpp are a part of. By working together in an inducing, repressing or cooperative fashion, these three genes signal certain imaginal disk cells to become the legs of the fly and the anterior/posterior and dorsal/ventral regions of the leg. Removing any one of them any of them has an immediate effect on the geographic expression of the others in the disk itself, which can be visualized with various staining techniques. Furthermore, the importance of these three genes can be seen in the fact that the absence of any one of them, will lead to the disk being unable to distillize into the adult leg structure.

Mei Yu Xu | Email: myx@student.umass.edu mRNA Localization and the Mechanisms Involved

ABSTRACT

Asymmetric distributions of proteins into particular areas of the cell are what the cells use to polarize themselves. Regional concentration of specific protein is established by mRNA localization. In order to understand cell regulation better, it is necessary to look at both cell fate determined by the localized proteins and the details of mRNA localization. This report reviews the purposes, features and mechanisms of mRNA localization. It presents various hypothesis, supportive experiments and their results and tries to answer two main questions: what is mRNA localization and how is it done?

Scott Zagame | Email: szagame@student.umass.edu Wing development in Drosophilia melanogaster

ABSTRACT

During early development of Drosophila, clusters of undifferentiated epithelial cells, or imaginal discs, are formed, which will later develop into the adult's limbs after molting. Wing morphogenesis involves the interactions of many proteins and transcription factors, especially wingless and decapentaplegic (dpp). In fact, the wing disc is formed by the interactions of these two proteins. The first step of wing development involves the outgrowth of the wing disc and formation of the wing's axes, the anterior/posterior axis, the proximal/distal axis, and the dorsal/ventral axis. Outgrowth of the wing involves the genes wingless and dpp, and starts from a group of cells expressing distal-less. Axis formation involves numerous genes including dpp, wingless, engrailed, hedgehog, and vestigial. Other steps involved in wing development includes the formation of the wing veins and wing hairs. Key genes involved in wing vein development include argos and rhomboid, while wing hair development is regulated by the genes wingless and inturned. Many of the genes expressed in wing development are involved in the differentiation of other imaginal discs of the fly, including the eye discs, limb discs, and genital discs. This conservation of genes between imaginal discs can help better understand this complex pathway to organ formation.

Phillip Damiani | Email: pdamiani@vasci.umass.edu Topic: Function of GLD-1 protein during C. elegans oocyte differentiation

ABSTRACT

The germline of Caenorhabditis elegans is organized in a linear fashion - the most distal germ cells remain in mitosis, those in the middle enter meiosis and proximal cells differentiate as sperm or oocytes. Two signal transduction pathways control the fate of the germ cells. One pathway controls the decision to remain in mitosis and the other, the sexual differentiation of the germ cells. The putative RNA binding protein, GLD-1, is the terminal regulator for oogenesis. Null and strong loss-of-function alleles of gld-1 abolish oogenesis and result in a sex-specific defect in the meiotic cell cycle progression. These germ cells subsequently return to mitosis and proliferate, forming germline tumors. Furthermore, the gld-1 (null) tumorous phenotype is not dependent on either chromosomal sex or somatic sexual phenotype. This phenotype requires that the regulatory pathway for sex determination be set in the female mode that normally leads to oogenesis. Recently, immunolocalization studies have shown that GLD-1 a cytoplasmic germline protein which displays differential accumulation during germline development. This further indicates that gld-1 is required directly for oogenesis and suggest that the gene may also have a role in regulating the differentiation of the female germ cells.

Created: 04/29/97 Updated: 05/12/97