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Class VI unconventional myosin is required for spermatogenesis in Drosophila
J L Hicks1, W M Deng, A D Rogat
1Department of Biology, Washington University, St. Louis, Missouri 63130, USA.
Abstract:
We have identified partial loss of function mutations in class VI unconventional myosin, 95F myosin, which results in male sterility. During spermatogenesis the germ line precursor cells undergo mitosis and meiosis to form a bundle of 64 spermatids. The spermatids remain interconnected by cytoplasmic bridges until individualization. The process of individualization involves the formation of a complex of cytoskeletal proteins and membrane, the individualization complex (IC), around the spermatid nuclei. This complex traverses the length of each spermatid resolving the shared membrane into a single membrane enclosing each spermatid. We have determined that 95F myosin is a component of the IC whose function is essential for individualization. In wild-type testes, 95F myosin localizes to the leading edge of the IC. Two independent mutations in 95F myosin reduce the amount of 95F myosin in only a subset of tissues, including the testes. This reduction of 95F myosin causes male sterility as a result of defects in spermatid individualization. Germ line transformation with the 95F myosin heavy chain cDNA rescues the male sterility phenotype. IC movement is aberrant in these 95F myosin mutants, indicating a critical role for 95F myosin in IC movement. This report is the first identification of a component of the IC other than actin. We propose that 95F myosin is a motor that participates in membrane reorganization during individualization.
Insights
Partial loss of function mutations in 95F myosin cause male sterility by disrupting spermatid individualization. This study identifies 95F myosin as a crucial motor protein for the individualization complex (IC) movement.
Area of Science:
- Cell Biology
- Developmental Biology
- Molecular Genetics
Background:
- Spermatogenesis involves the formation of 64 interconnected spermatids from germ line precursors.
- Individualization, a critical step in spermatogenesis, requires the formation and movement of the individualization complex (IC).
- The molecular machinery driving IC movement and membrane reorganization during individualization remains incompletely understood.
Purpose of the Study:
- To identify novel components of the individualization complex (IC).
- To investigate the role of class VI unconventional myosin, 95F myosin, in spermatid individualization.
- To elucidate the function of 95F myosin in male fertility.
Main Methods:
- Identification and characterization of partial loss-of-function mutations in the 95F myosin gene.
- Analysis of 95F myosin localization within the IC during spermatogenesis.
- Assessment of male fertility and spermatid morphology in wild-type and mutant flies.
- Complementation of male sterility via germ line transformation using 95F myosin heavy chain cDNA.
Main Results:
- Partial loss-of-function mutations in 95F myosin lead to male sterility due to defects in spermatid individualization.
- 95F myosin is identified as a component of the IC, localizing to its leading edge in wild-type testes.
- Mutations causing reduced 95F myosin levels result in aberrant IC movement and incomplete spermatid individualization.
- Germ line transformation rescues the male sterility phenotype, confirming the role of 95F myosin.
Conclusions:
- 95F myosin is essential for the proper movement of the individualization complex (IC) during spermatogenesis.
- This study is the first to identify a component of the IC, other than actin, involved in membrane reorganization.
- 95F myosin functions as a motor protein critical for successful spermatid individualization and male fertility.