Date of Award:

5-1971

Document Type:

Dissertation

Degree Name:

Doctor of Philosophy (PhD)

Department:

Biology

Department name when degree awarded

Zoology

Committee Chair(s)

James T. Bowman

Committee

James T. Bowman

Committee

Paul B. Carter

Committee

Hugh P. Stanley

Committee

Eldon J. Gardner

Committee

John R. Simmons

Abstract

In order to study the genetic control of spermiogenesis, recessive, male-sterile, autosomal mutants of Drosophila melanogaster were induced with ethyl methanesulfonate. A total of 31 mutants were recovered, 15 of which were located on the second chromosome and 16 on the third chromosome. Eight second- and 6 third-chromosome mutants demonstrating sterility in all homozygous males were used for further analysis.

Complementation tests showed that 2 of the 8 second chromosome mutants (and none of the 6 third chromosome mutants) were noncomplementing, indicating that two of the mutants produced were alleles of the same locus. Mapping of the second chromosome mutants indicated a clustering near the heterochromatin in the left arm.

In 2 of the mutants, spermiogenesis was studied with the light and electron microscopes. Mutant C2-3 has an anomaly associated with cytokinesis accompanying 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 normal nebenkern does. In the mutant these two mitochodrial 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 form, one at each contact point between the membranes of the primary mitochondrial derivative and the membranes around the four axonemes contained in the common cytoplasmic unit. The groups of 4 spermatids almost complete maturation before the bundles degenerate.

Mutant C2-10 is characterized by two anomalies: (1) disruption of the axonemal complex, and (2) formation of multiple paracrystalline bodies within the primary mitochondrial derivative. This mutant undergoes limited elongation with some variation between bundles of maturing spermatids. Axonemal complexes apparently complete differentiation even through disrupted and scattered in the cytoplasm. Mitochondrial derivatives are often very large and contain several paracrystalline bodies. The paracrystalline bodies form within the primary mitochondrial derivatives at contact points between the membranes of the derivative and the cytoplasmic membranes. Abnormally large numbers of microtubules are observed within spermatids containing large mitochondrial derivatives and appear to be rather uniformly distributed around the derivatives. The large derivative size is presumed to be due to failure of normal elongation. Spermatids degenerate rather late in the maturation process.

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