Social modulation of oogenesis and egg laying in Drosophila melanogaster

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A genetic melanotic neoplasm of Drosophila melanogaster

The construction of mature fruiting bodies occurs during the culmination stage of development of Dictyostelium discoideum. These contain at least two different cell types, spores and stalks, which originate from an initially homogenous population of vegetative amoebas. As an attempt to identify proteins whose synthesis is regulated in each cell type during differentiation, we have analyzed the two-dimensional profiles of proteins synthesized by spore and stalk cells during the culmination stage. We have identified 5 major polypeptides which are specifically synthesized by spore cells during culmination and 9 which are only made by stalk cells. Furthermore, synthesis of about 20 polypeptides appears to be enriched either in the spore or in the stalk cells. We also show that synthesis of actin, a major protein synthesized during Dictyostelium development, is specifically inhibited in the spore cells during culmination. Synthesis of most of the cell type-specific proteins initiates at 19–20 hr, during culmination. Moreover, the proteins whose synthesis is induced after formation of tight aggregates, the time when the major change in gene expression occurs, are not specifically incorporated into spores or stalk cells, and appear to be synthesized by both cell types. We conclude that a new class of genes is expressed during the culmination stage in Dictyostelium, giving rise to specific patterns of protein synthesis in spore and stalk cells.     

A genetic variant of beta-glucuronidase in Drosophila melanogaster

The beta-glucuronidase activity of Drosophila melanogaster exists as two chromatographically separable forms, both of which are glycoproteins. Form I is membrane-bound in vivo, has a pI of 8.0-8.5, and can be irreversibly inactivated either by incubation at 55 degrees C for 20 min or by incubation at 37 degrees C in the presence of 6 M urea. Form II exists both membrane-bound as well as membrane-free, has a pI of 4.5, and is resistant to the conditions which inactivate form I. The two forms are similar in Km and Vmax for the artificial substrate 4-methylumbelliferyl-beta-D-glucuronide and both forms are precipitated by antibody to form II. A natural genetic variant, beta-GluL1, completely lacks from I beta-glucuronidase. This variant behaves in a co-dominant fashion for the determination of the presence of form I and has been localized to the extreme distal portion of chromosome 3R. Other data indicate that at least one genetic determinant for the amount of form II is also localized to this portion of chromosome 3R.     

Regulation of the vitellogenin receptor during Drosophila melanogaster oogenesis

In many insects, development of the oocyte arrests temporarily just before vitellogenesis, the period when vitellogenins (yolk proteins) accumulate in the oocyte. Following hormonal and environmental cues, development of the oocyte resumes, and endocytosis of vitellogenins begins. An essential component of yolk uptake is the vitellogenin receptor. In this report, we describe the ovarian expression pattern and subcellular localization of the mRNA and protein encoded by the Drosophila melanogaster vitellogenin receptor gene yolkless (yl). yl RNA and protein are both expressed very early during the development of the oocyte, long before vitellogenesis begins. RNA in situ hybridization and lacZ reporter analyses show that yl RNA is synthesized by the germ line nurse cells and then transported to the oocyte. Yl protein is evenly distributed throughout the oocyte during the previtellogenic stages of oogenesis, demonstrating that the failure to take up yolk in these early stage oocyte is not due to the absence of the receptor. The transition to the vitellogenic stages is marked by the accumulation of yolk via clathrin-coated vesicles. After this transition, yolk protein receptor levels increase markedly at the cortex of the egg. Consistent with its role in yolk uptake, immunogold labeling of the receptor reveals Yl in endocytic structures at the cortex of wild-type vitellogenic oocytes. In addition, shortly after the inception of yolk uptake, we find multivesicular bodies where the yolk and receptor are distinctly partitioned. By the end of vitellogenesis, the receptor localizes predominantly to the cortex of the oocyte. However, during oogenesis in yl mutants that express full-length protein yet fail to incorporate yolk proteins, the receptor remains evenly distributed throughout the oocyte.     

A new peroxinectin-like gene preferentially expressed during oogenesis and early embryogenesis in Drosophila melanogaster

Several peroxidase isozymes have been described in Drosophila melanogaster. We describe a peroxinectin-like gene (Dpxt) in D. melanogaster. Peroxinectin is a cell-adhesive hemoperoxidase which binds superoxide dismutase and mediates blood cells attachment and spreading in the crayfish Pacifastacus leniusculus. The Dpxt predicted protein has a putative RGD-integrin binding tripeptide. The Dpxt mRNA is present in high amounts in late oogenesis and in early embryogenesis until the cellular blastoderm stage. It is virtually absent at other stages of the Drosophila life cycle, suggesting that Dpxt function is restricted to the early stages of fly development.     

Associations between female remating behavior, oogenesis and oviposition in Drosophila melanogaster and Drosophila pseudoobscura

An association between female remating behavior, oogenesis and oviposition was examined in Drosophila melanogaster and Drosophila pseudoobscura to investigate mechanisms that elicit remating. Females receptive to remating oviposited more eggs in both species; however, the species differed in the association between remating behavior and the number and distribution of oocyte stages. We found no differences in the number of either developing eggs of different stages or mature eggs between female D. pseudoobscura that were either receptive or nonreceptive to remating. In contrast, D. melanogaster females that are receptive to remating had significantly more mature eggs in the ovaries than nonreceptive females. Nonremating females had a significantly greater number of immature, vitellogenic oocytes. These results suggest that factors associated with oogenesis are related to female remating behavior in D. melanogaster but not in D. pseudoobscura. We discuss these results in conjunction with other evidence on the role male ejaculatory components play in mediating female remating behavior.     

A genetic analysis of the cytological region 46C-F containing the Drosophila melanogaster homolog of the jun proto-oncogene

The cytogenetic region 46C-F on the right arm of Drosophila chromosome 2, which contains the homolog of the human jun proto-oncogene, has been genetically mapped and characterized. This project led to the identification and characterization of a Jra (jun-related antigen) mutation, which has been described in detail elsewhere. Three mutagens, EMS, DEB and gamma-rays, were used to isolate 126 lethal lines for this interval. Complementation analysis of the 126 lethal lines identified 29 lethal complementation groups in the region; nine of which have now been correlated with known genes or phenotypes. The region has been subdivided into ten intervals using various small deletions, seven intervals in 46C/D and three intervals in 46E/F. Sixteen P-element lines have been mapped to this interval and are allelic to eight of our complementation groups. The remaining unidentified complementation groups have been analyzed for critical phase, which is when the first observable defect arises and/or when death occurs. There are twelve embryonic lethal groups and seven larval lethal groups. Three lines show visible abnormalities in gut and tracheal development prior to death.     

Adherens junction remodeling by the Notch pathway in Drosophila melanogaster oogenesis

Identifying genes involved in the control of adherens junction (AJ) remodeling is essential to understanding epithelial morphogenesis. During follicular epithelium development in Drosophila melanogaster, the main body follicular cells (MBFCs) are displaced toward the oocyte and become columnar. Concomitantly, the stretched cells (StCs) become squamous and flatten around the nurse cells. By monitoring the expression of epithelial cadherin and Armadillo, I have discovered that the rate of AJ disassembly between the StCs is affected in follicles with somatic clones mutant for fringe or Delta and Serrate. This results in abnormal StC flattening and delayed MBFC displacement. Additionally, accumulation of the myosin II heavy chain Zipper is delayed at the AJs that require disassembly. Together, my results demonstrate that the Notch pathway controls AJ remodeling between the StCs and that this role is crucial for the timing of MBFC displacement and StC flattening. This provides new evidence that Notch, besides playing a key role in cell differentiation, also controls cell morphogenesis.     

Dmoesin controls actin-based cell shape and polarity during Drosophila melanogaster oogenesis

Ezrin, Radixin and Moesin (ERM) proteins are thought to constitute a bridge between the actin cytoskeleton and the plasma membrane (PM). Here we report a genetic analysis of Dmoesin, the sole member of the ERM family in Drosophila. We show that Dmoesin is required during oogenesis for anchoring microfilaments to the oocyte cortex. Alteration of the actin cytoskeleton resulting from Dmoesin mutations impairs the localization of maternal determinants, thus disrupting antero-posterior polarity. This study also demonstrates the requirement of Dmoesin for the specific organization of cortical microfilaments in nurse cells and, consequently, mutations in Dmoesin produce severe defects in cell shape.     

Dosage of 5 S and ribosomal genes during oogenesis of Drosophila melanogaster

During growth, the Drosophila egg chamber increases its DNA content over a thousandfold, mainly by polyploidization of the nurse cell nuclei. We wanted to determine if 5 S and ribosomal genes are replicated to the same extent as the remaining DNA. Egg chambers were mass fractionated to represent different size classes and, therefore, different stages of oogenesis. Nucleic acids were extracted from each class of egg chambers, and after removal and quantitation of the RNA, the content of 5 S and ribosomal genes in the different DNA fractions was assayed by filter hybridization. Diploid DNA and DNA from polytene salivary gland cells served as references. It was concluded that: (1) Ribosomal genes become underreplicated as oogenesis proceeds, but to a much lower extent than in polytene chromosomes of salivary glands of the same organism. (2) By contrast, 5 S genes are equally replicated in egg chambers of all stages of oogenesis. (3) Notwithstanding the large increase in DNA content of egg chambers during oogenesis, the increase in total RNA content (mostly ribosomal RNA) is over 15 times as large.     

Two discrete modes of histone gene expression during oogenesis in Drosophila melanogaster

We have used in situ hybridization to ovarian tissue sections to study the pattern of histone gene expression during oogenesis in Drosophila melanogaster. Our studies suggest that there are two distinct phases of histone gene expression during oogenesis. In the first phase, which occurs during early to middle oogenesis (stages 5-10A), we observe a mosaic pattern of histone mRNA in the 15 nurse cells of the egg chamber: some cells have very high levels of mRNA, while others have little or no mRNA. Our analysis suggests that there is a cyclic accumulation and subsequent degradation of histone mRNA in the egg chamber and that very little histone mRNA is transported into the growing oocyte. Moreover, since the endomitotic replication cycles of the nurse cells are asynchronous during this period, the mosaic distribution of histone message would suggest that the expression of the histone genes in each nurse cell nucleus is probably coupled to DNA replication as in most somatic cells. The second phase begins at stage 10B. During this period, histone gene expression appears to be "induced" in all 15 nurse cells of the egg chamber, and instead of a mosaic pattern, high levels of histone mRNA are found in all cells. Unlike the earlier phase, this expression is apparently uncoupled from the endomitotic replication of the nurse cells (which are completed by the end of stage 10A). Moreover, much of the newly synthesized histone mRNA is transported from the nurse cells into the oocyte where it accumulates and is stored for use during early embryogenesis. Finally, we have also observed tightly clustered grains within nurse cell nuclei in non-denatured tissue sections. As was the case with cytoplasmic histone mRNA, there is a mosaic distribution of nuclear grains from stages 5 to 10A, while at stage 10B, virtually all nurse cell nuclei have grain clusters. These grain clusters appear to be due to the hybridization of nurse cell histone gene DNA to our probe, and are localized in specific regions of the nucleus.