Abstract
Males of the genus Drosophila produce sperm of remarkable length. Investigation of giant sperm production in Drosophila melanogaster has demonstrated that specialized actin and microtubule structures play key roles. The gene yuri gagarin (yuri) encodes a novel protein previously identified through its role in gravitaxis. A male-sterile mutation of yuri has revealed roles for Yuri in the functions of the actin and tubulin structures of spermatogenesis. Yuri is a component of the motile actin cones that individualize the spermatids and is essential for their formation. Furthermore, Yuri is required for actin accumulation in the dense complex, a microtubule-rich structure on the sperm nuclei thought to strengthen the nuclei during elongation. In the yuri mutant, late clusters of syncytial nuclei are deformed and disorganized. The basal bodies are also mispositioned on the nuclei, and the association of a specialized structure, the centriolar adjunct (CA), with the basal body is lost. Some of these nuclear defects might underlie a further unexpected abnormality: sperm nuclei occasionally locate to the wrong ends of the spermatid cysts. The structure of the axonemes that grow out from the basal bodies is affected in the yuri mutant, suggesting a possible role for the CA in axoneme formation.
Highlights
A unique feature of the genus Drosophila is the formation of unusually long sperm tails
This marked expansion in sperm length reflects an unusual aspect of spermatogenesis in these organisms: in contrast to other species in which an intraflagellar transport system is used for growth of the sperm flagellum (Scholey, 2006), Drosophila sperm axonemes are assembled in syncytial cysts by a mechanism that does not require, and is not limited by, this system (Han et al, 2003; Sarpal et al, 2003)
The distinctive molecular mechanisms needed for this process include a motile filamentous actin system that traverses the entire length of the sperm tails, removing excess cytoplasm and investing each sperm in its own plasma membrane
Summary
A unique feature of the genus Drosophila is the formation of unusually long sperm tails. Sperm lengths of millimeters are common within this group, with the 1.8 mm sperm of D. melanogaster being fairly typical This marked expansion in sperm length reflects an unusual aspect of spermatogenesis in these organisms: in contrast to other species in which an intraflagellar transport system is used for growth of the sperm flagellum (Scholey, 2006), Drosophila sperm axonemes are assembled in syncytial cysts by a mechanism that does not require, and is not limited by, this system (Han et al, 2003; Sarpal et al, 2003). Cytodifferentiation during spermatogenesis in Drosophila melanogaster, PhD thesis, Rijksuniversiteit Leiden, The Netherlands, 1971) (Tokuyasu, 1974)
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