James T. Bowman

Fine structure of normal spermatid differentiation in Drosophila melanogaster.

Spermiogenesis in Drosophila melanogaster has been divided into eleven developmental stages based upon the fine structure of differentiating organelles. Emphasis is placed on the relative state of development of all organelles in each stage. This information will facilitate the analysis of subtle alterations in spermatid differentiation produced by mutations in the genome or by any other experimental manipulation. New details of organelle development are reported including distinctive associations of cytoplasmic microtubules with both the endoplasmic reticulum and the nuclear envelope. The centriolar complex is postulated to be the main organizational center in spermatid differentiation.

Genetic control of spermiogenesis in Drosophila melanogaster: The effects of abnormal cytoplasmic microtubule populations in mutant ms(3)10R and its colcemid-induced phenocopy

Spermiogenesis has been examined in an autosomal male-sterile mutant (ms(3)10R) of Drosophila melanogaster and in a phenocopy induced by Colcemid. Nuclei in mutant spermatids always show condensation of chromatin but usually do not elongate. The normal sheath of cytoplasmic microtubules attached to the nuclear envelope is lacking in these nonelongate nuclei. Infrequently, mutant nuclei are seen in which an incomplete population of cytoplasmic microtubules surrounds the nucleus, and these nuclei show more nearly normal morphology. Axonemal complexes in mutant spermatids elongate, and tails have numerous, but somewhat disorganized, cytoplasmic microtubule populations. Treatment of wild-type flies with Colcemid removes almost all the cytoplasmic microtubules. The chromatin of differentiating sperm nuclei in Colcemid-treated testes condenses, but the sperm do not elongate. These nuclei are phenocopies of the most commonly found nuclei in the testes of mutant flies. In Colcemid-treated individuals, the axonemal complexes do not elongate beyond the length attained by normal primary spermatocytes. We conclude that normal differentiation, particularly modeling of the sperm head, requires the presence of a normal population of cytoplasmic microtubules.

Gene modulation in Drosophila: dosage compensation and relocated v + genes.

The v+ gene of Drosophila and its associated enzyme, tryptophan pyrrolase, were employed in a study of the relationship between dosage compensation and the location of the gene in the genome. Enzyme assays performed on various genotypes indicate that although differently positioned genes may specify different enzyme activities, they still show dosage compensation. In each rearrangement examined, the enzyme activity associated with the gene is at least twice as much in males as it is in females. The relevance of this and earlier data with respect to models for regulation is discussed.

Gene modulation in Drosophila: Dosage compensation of Pgd+ and Zw+ genes

The sex-linked Pgd+ and Zw+ genes of Drosophila melanogaster and their associated enzyme activities 6-phosphogluconate dehydrogenase and glucose 6-phosphate dehydrogenase were employed in an analysis of the relationship between dosage compensation and the location of genes in the genome. In the genotypes examined, the enzyme activity specified by each copy of the gene is twice in males what it is in females. This is true of normal, structurally rearranged, and duplication genotypes. Dosage compensation, therefore, is a regulatory function associated with single structural genes or small chromosomal segments and does not depend on the genes physical location on the X chromosome.

The effect of vinblastine on spermiogenesis in Drosophila melanogaster: evidence for two functional classes of cytoplasmic microtubules.

Sperm development has been examined in vinblastine-treated imagos of Drosophila melanogaster. In treated flies, most cytoplasmic microtubules of the spermatids were absent with the exception of the cross-linked nuclear-sheath microtubules. Spermatids that had these cross-linked microtubules expressed variable degrees of normal nuclear differentiation which could be correlated with the numbers of cross-linked microtubules. In addition to nuclear effects, axonemes of vinblastine-treated spermatids did not elongate and the Nebenkern derivatives showed highly aberrant profiles. Based on these observations, cytoplasmic microtubules appear to be prerequisite subcellular elements for the normal differentiation of sperm in Drosophila melanogaster. Additionally, the data from this study suggest that there are two distinct functional classes of cytoplasmic microtubules in spermatids of Drosophila melanogaster, one involved in nuclear differentiation and the other in the generation of the flagellum. Furthermore, it is proposed that the nuclear-sheath microtubules function as subcellular mediators of nuclear shape change.

Genetic control of spermiogenesis in Drosophila melanogaster: an autosomal mutant (ms(2)3R) demonstrating failure of meiotic cytokinesis

The ultrastructure of spermatid differentiation in an autosomal male sterile mutant of Drosophila melanogaster is described. The mutant ms(2)3R is characterized by failure of the cytokinetic divisions which normally accompany meiosis. The primary spermatocyte undergoes nuclear division, but a failure of cytokinesis leaves 4 spermatids to develop within a common cytoplasm. The mitochondria fuse, usually forming a single large nebenkern, which then divides into two approximately equal parts as does a normal nebenkern. In the mutant, these two mitochondrial derivatives usually undergo further division generally giving rise to 8 or fewer mitochondrial derivatives. Multiple paracrystalline bodies are often observed in the primary mitochondrial derivatives. Up to 4 paracrystalline bodies may be observed in a single section of a derivative, one at each contact point between the membranes of the primary mitochondrial derivatives and the membranes around the 4 axonemes contained in the common cytoplasmic unit. The units of four spermatids almost complete maturation before the bundles degenerate. It appears that, with the exception of the nebenkern and its derivatives, cytoplasmic separation is not a prerequisite for the normal differentiation of most spermatid organelles.

Genetic control of spermiogenesis in Drosophila melanogaster: an autosomal mutant (ms(2)10R) demonstrating disruption of the axonemal complex

The ultrastructure of spermatid differentiation in an autosomal male sterile mutant of Drosophila melanogaster is described. The mutant ms(2)10R is characterized by two anomalies: (a) disruption of the axonemal complex, and (b) formation of multiple paracrystalline bodies within abnormally large primary mitochondrial derivatives. The mutant undergoes limited elongation with some variation between maturing bundles of spermatids. Components of the axonemal complex apparently complete differentiation even though disrupted and scattered in the cytoplasm. Mitochondrial derivatives are often very large and contain several paracrystalline bodies which form at contact points between the membranes of the derivatives and the cytoplasmic membranes. Abnormally large numbers of microtubules are observed within spermatids containing large mitochondrial derivatives. The large size of mitochondrial derivatives in transverse section is presumed to be due to a failure of normal elongation. Spermatids degenerate rather late in the maturation process. No fully mature spermatids were observed.

X-ray-induced reversion of thewhite-ivory mutant ofDrosophila melanogaster

Following X irradiation,wi reverts in oogonia and in spermatogonia. following treatment of adult females,wi reverts equally frequently in homozygotes and deficiency heterozygotes. Induced reversions are commonly recovered as clusters, indicating that they are of gonial origin. In contrast towi, two partial reversions recombine normally withwch. One of these has been tested for X-ray-induced reversion and found to be stable.

Terminal synthesis of xanthommatin in Drosophila melanogaster. I. Roles of phenol oxidase and substrate availability.

Eye color mutants of Drosophila melanogaster are known which block the conversion of 3-hydroxykynurenine to xanthommatin. It has been proposed that this reaction depends on the presence of 3-hydroxykynurenine and a redox system maintained by phenol oxidase activity. The mutants st and ltd lack throughout development detectable amounts of 3-hydroxykynurenine or its metabolic derivatives. When the substrate is fed or injected, these mutants fail to form xanthommatin even though phenol oxidase activity is normal. The mutant cd accummulates excessive amounts of 3-hydroxykynurenine, has normal phenol oxidase activity, but is also deficient in xanthommatin formation. Mutants are also known which lack phenol oxidase activity but nevertheless form xanthommatin. It is concluded that the proposed relationship between 3-hydroxy-kynurenine and phenol oxidase activity is not sufficient to explain the in vivo synthesis and regulation of synthesis of xanthommatin in Drosophila. The bearing of these findings on the actual mode of synthesis is discussed.

Genetic control of spermiogenesis in Drosophila melanogaster: the effects of abnormal association of centrosome and nucleus in mutant ms(1)6S.

Mutant ms (1)6S of Drosophila melanogaster is characterized by a spectrum of abnormalities of spermatid differentiation. Included in these are failure of the basal body to make normal attachment to the nucleus, failure of acrosomes to develop, and lack of a normal population of perinuclear microtubules. There is also a failure of normal chromatin condensation and nuclear elongation. The mitochondria do not form a normal nebenkern, but nevertheless fuse, elongate, and develop paracrystalline bodies. The number of normal axonemes is markedly reduced as a result of the failure of some centrioles to form basal bodies. All of these aberrations can be related to defective interactions of the “centrosome” or “microtubule-organizing-centre” with other organelles. The analysis of spermiogenesis in this mutant further clarifies the roles of microtubules in nuclear condensation and elongation and in cellular elongation in general.