Joan H. Caulton

Developmental fate of pole cells in Drosophila melanogaster

Abstract Pole cells, in addition to being precursors of the primordial germ cells, have been thought to give rise to vitellophages and/or midgut epithelial cells. This study presents a reexamination of the potential fates of these cells in Drosophila melanogaster . Pole cell movements have been traced using both morphological criteria and autoradiography following transplantation of radioactively labeled pole cells. After the completion of gonad formation most pole cells are found in the gonads. Some pole cells enter the yolk mass, but these are completely enclosed within the yolk membrane. These cells do not become vitellophages and may later degenerate. A low percentage of pole cells are found loosely associated with tissues near the gonads. Pole cells are also found in the hindgut lumen, anal opening, and exterior of the embryo. We propose that, although less than half of the pole cells formed (or injected) ultimately reach the gonads, there is no other major fate for the pole cells. The “extra” pole cells either get trapped in neighboring tissues, degenerate in the yolk, or are excreted.

Loss of centrioles and polyploidization in follicle cells of Drosophila melanogaster

Abstract Centrioles of the nurse cells of Drosophila have been shown to move into the oocyte prior to polyploidization of the nurse cells. In order to determine whether or not centriolar loss always occurs in polyploid insect cells, the follicular epithelium of the Drosophila ovary was studied. The DNA content of the cells was determined by cytophotometry of Feulgen-stained squash preparations. The first two endomitotic replications occur at stage 7 and 8. Two additional replications occur prior to stage 11, but the DNA content appears to be under-replicated. Centrioles are found in follicle cells until stage 10 at which time they are no longer present. At the inception of polyploidization the centrioles are no longer closely associated with each other or the nuclear envelope. Instead, they are located adjacent to the plasma membrane at the basal surface. These results closely parallel the previous results found for the nurse cells. Hence, it may be a general observation that centrioles are gradually lost in polyploid insect cells.

Ultrastructural studies of oocytes and embryos derived from female flies carrying the grandchildless mutation in Drosophila subobscura

Abstract The maternal effect mutant grandchildless in Drosophila subobscura has been analyzed with the electron microscope. The original mutation was linked to a visible genetic marker and established in a balanced stock. Oocytes and early embryos were examined by both transmission and scanning electron microscopy. The earliest defect is seen in mutant eggs and occurs at the end of oogenesis. In the cortex, at both the anterior and the posterior tips, regions appear which are free of ribosomes, mitochondria, and other cytoplasmic organelles. Most of the polar granules are included in these regions at the posterior tip. Following oviposition, this cytoplasmic segregation is no longer observed and most polar granules have disappeared. The few remaining granules are presumed to derive from the peripheral polar plasm which does not become segregated. During embryogenesis there is a retarded movement of nuclei to the anterior and posterior cortices. At the posterior tip nuclei are delayed in reaching the lateral sides and never move directly into the posterior polar plasm. Pole cells never form. After the last syncytial division the lateral nuclei move under the posterior polar plasm to complete the blastoderm. The posterior polar plasm itself protrudes during blastoderm formation as long cytoplasmic extensions which separate from the blastoderm as cytoplasmic blebs. Neither polar granules nor mitochondria are found in these blebs. The grandchildless phenotype is due to the failure of nuclei to migrate directly into the posterior polar plasm. The defect in the polar plasm presumably is related to the process in mature eggs whereby portions of the cortex become segregated at both anterior and posterior tips. This process may change the properties of the posterior polar plasm so that nuclei do not penetrate into it.

Pole cells of Drosophila melanogaster in culture: Normal metabolism, ultrastructure, and functional capabilities☆

Abstract The metabolism, ultrastructure, and function of mass-isolated pole cells were examined during short-term culture in vitro. In addition to demonstrating that these cells functioned normally in culture, a number of new features of embryonic pole cells were discovered. Cell populations isolated from Renografin density gradients were incubated in medium containing tritiated valine, uridine, or thymidine. Although pole cells incorporated similar amounts of valine into protein as other embryonic cells throughout the first 6 hr in culture, they began to synthesize RNA only after 2 hr in culture. Approximately 30% of the pole cells synthesized DNA in vitro and this synthetic activity occurred largely during the first hour of culture. An ultrastructural analysis of colcemid-treated cells showed that 10% of the pole cells divide shortly after placement in culture. During pole cell culture in vitro, polar granules and nuclear bodies fragment and disperse so that they are eventually not detected in these cells. These changes also occur during pole cell development in vivo. Finally, we have obtained 25 to 33% germ line mosaicism among the fertile adults which were derived from embryos receiving transplantation of isolated pole cells before and after culture in vitro. These results demonstrate that these cells are able to follow their normal developmental program in vitro and are able to give rise to functional germ cells in vivo.

Developmental lesions in the Agametic mutant of Drosophila melanogaster

Abstract Agametic , a maternal-effect mutation, causes the absence of germ cells in approximately 40% of the gonads of flies derived from homozygous females. The nature of the deficiency in the eggs produced by these flies was examined. Ultrastructural abnormalities were seen in the polar granules of some eggs shortly after fertilization. Although a normal number of pole cells form, some are abnormal with degenerating polar granules and nuclear bodies and they contain myeloid bodies. The pole cells reach the gonads and at 14 hr of development all the gonads contain germ cells. However, in 40% of the gonads the germ cells become necrotic and disappear. Thus, the source of agametic gonads in the adult is embryonic death of pole cells in some gonads. To test whether this gonadal death is an autonomous deficiency of the mutant pole cells, mosaic pole cell populations were produced by reciprocal pole cell transplantation. In both types of transplants, the mutant pole cells died autonomously. In eight instances gonads containing only donor pole cells were obtained. Since mutant pole cells die when wild-type pole cells normally begin dividing, we suggest that the lesion affects the ability of these mutant pole cells to reenter the cell cycle.

Rapid appearance of multivesicular bodies in the cortex of Drosophila eggs at ovulation

Abstract Following activation of Drosophila oocytes, acid phosphatase-positive multivesicular bodies (MVB) rapidly form in the cortex. From observations of eggs during the first few minutes of activation, MVBs are thought to form from invaginations of the oolemma. Since there is no evidence for turnover of vitellogenin receptors at earlier times, it is postulated that these receptors are synchronously removed at activation.

Induction of glycoprote1n mating factors in diploid yeast of Hansenula wingei by vanadium salts or chelating agents

Abstract In the yeast H, wingei, mating is initiated by sexual agglutination between opposite mating types (strains 5 and 21). The cell wall factors responsible for this agglutination reaction are complementary glycoproteins (5-factor and 21-factor). In the diploid, the synthesis of 5-factor and 21-factor is under the control of metal ions. Addition of 0.4 mM each of sodium metavanadate and sodium molybdate to a diploid culture will induce the synthesis of 5-factor. Synthesis of 21-factor in the diploid is induced by adding a chelating agent (1 mM Na2 EDTA) to minimal medium containing 0.63 % yeast extract.

Chapter 10 Induction of Haploid Glycoprotein Mating Factors in Diploid Yeasts

Publisher Summary This chapter discusses induction of haploid glycoprotein mating factors in diploid yeasts. It illustrates the steps in the alternation of generations of Hansenula wingei , a heterothallic yeast. The two opposite mating types are haploid strains 5 and 21. Both haploids are constitutively agglutinative and, while cell suspensions of each are stable separately, they agglutinate immediately when mixed together. Following agglutination, the cells conjugate pairwise, producing a 5 × 21 diploid hybrid which is nonagglutinative and a nonmater. The diploid can be either grown vegetatively or sporulated if transferred to special media. The sporulation process results in a tetrad of meiotic products: two spores of mating type 5 and two spores of mating type 21, indicating that these mating types are allelic. In the chapter, methods are presented that alter one step of the normal life cycle—the mating response of the diploid. Conditions are discussed that induce the diploid to become sexually agglutinative and therefore able to participate in the first step in conjugation–cellular recognition. Biology of the yeast H. wingei and control of haploid-mating functions in the diploid are discussed. Significance of induction of sex-specific cell surface glycoproteins in the diploid is also discussed.