OOGENESIS IN FEMALE STERILE (1) 1304 MUTANT OF DROSOPHILA MELANOGASTER
Drosophila melanogaster females homozygous for the gene, fs(1)1304 (1-19 (+OR-) 2), are sterile and produce cytologically abnormal ovaries. These ovaries are characterized by nurse cells of abnormal nuclear and nucleolar morphology, a small oocyte which comes to be surrounded by multiple layers of follicle cells, and secretion of morphologically abnormal vitelline membrane, chorion, and dorsal appendages. Most of the fs/fs egg chambers degenerate during the vitellogenic stages of oogenesis. Some egg chambers do complete development; however, the resulting oocytes are never laid. Heterozygous fs females and hemizygous males are fertile. The major objective of this dissertation is to characterize the fs(1)1304 mutant in an effort to assign a function to the wild type allele of this mutant gene. Studies have been carried out to determine (1) whether fs(1)1304 affects the ovaries themselves or their environment, and (2) to which ovarian cell type and cellular function the mutant phenotype can be attributed. Polyacrylamide gel electrophoresis of ovarian and hemolymph proteins suggest that fs/fs females accumulate proteins in the hemolymph in amounts which are greater than those found in the wild type females. These proteins are sequestered by the mutant ovaries at an abnormally slow rate. The multiple layer of follicle cells around the fs oocyte probably prevents the vitellogenin molecule from reaching the oocyte surface. Neither juvenile hormone nor ecdysone treatment enhances vitellogenesis in fs/fs ovaries. Ovarian transplantation experiments show that fs(1)1304 behaves autonomously. The abdominal environment of this mutant, including the hormonal milieu is normal, and the genetic defect is endogenous to the ovary. Cytological studies show that one of the most visible effects of the fs(1)1304 gene is on the organization of chromatin in the nurse cells. The homologs of fs/fs nurse cell chromosomes are tightly associated with each other and fail to dissociate normally during the later developmental stages. Since this abnormality is observed during the earliest stages of egg chamber development, we suggest that the primary effect of the gene is on the nurse cell chromatin. A looser association of DNA strands is apparently necessary for the endomitotic DNA replications to occur normally in the nurse cells. Cytophotometric measurements of DNA-Feulgen levels show that nurse nuclei from fs/fs females undergo one or two fewer DNA replication cycles when compared with wild type nurse nuclei, although equivalent amounts of DNA are found in the follicle cells from wild type and mutant ovaries. Correlated with the abnormal organization of the chromatin in the nurse cell nuclei of fs/fs females is the abnormal organization of the nucleolar material as well as the instability of RNA in these nuclei. Sectioned nurse cell nuclei from the mutant contain relatively few, large nucleolar fragments as compared to those from heterozygous fs females. Autoradiographic analysis of incorporation of ('3)H-uridine in vivo and analysis of ('3)H-uridine incorporation into RNA in vitro suggest that RNA from fs/fs ovaries is degraded at a higher rate than that from control ovaries. Electrophoretic analysis suggests that the RNA class affected is ribosomal RNA. It is suggested that fs/fs females are unable to produce an adequate supply of stable RNA for storage in the developing oocyte. The pathological nature of fs/fs nurse cells renders them relatively ineffective in supplying the growing oocyte with nutrients. Such an ooctye is smaller in size than that of wild type ovaries. This causes the follicle cells to form multiple layers around the oocyte, for they do not have a large enough surface area to cover. The secretion of morphologically abnormal oocyte coverings may be attributed to the unusual crowding of follicle cells around the oocyte.
PAMELA KHIPPLE MULLIGAN,
"OOGENESIS IN FEMALE STERILE (1) 1304 MUTANT OF DROSOPHILA MELANOGASTER"
(January 1, 1980).
Dissertations (1962 - 2010) Access via Proquest Digital Dissertations.