Cytochrome c1-like is required for mitochondrial morphogenesis and individualization during spermatogenesis in Drosophila melanogaster.

Drosophila testis is an excellent system for studying the process from germ stem cells to motile sperm, including the proliferation of male germ cells, meiosis of primary spermatocyte, mitochondrial morphogenesis, and spermatid individualization. We previously demonstrated that the ocnus (ocn) plays an essential role in male germ cell development. Among those genes and proteins whose expression levels were changed due to ocn knockdown, the cytochrome c1-like (cyt-c1L) was downregulated significantly. Here, we showed that cyt-c1L was highly expressed in the testis of D. melanogaster. Knockdown or mutation of cyt-c1L in early germ cells of flies resulted in male sterility. Immunofluorescence staining exhibited that cyt-c1L knockdown testis had no defects in early spermatogenesis; however, in late stages, contrast to many individualization complexes (ICs) composed by F-actin cones appeared at different positions in control testes, no actin cones or ICs were observed in cyt-c1L knockdown testes. Furthermore, no mature sperms were found in the seminal vesicle of cyt-c1L knockdown testes whereas the control seminal vesicle was full of mature sperms with needle-like nuclei. cyt-c1L knockdown also caused abnormal mitochondrial morphogenesis during spermatid elongation. Excessive apoptotic signals were accumulated in the base of cyt-c1L knockdown fly testes. These results suggest that cyt-c1L may play an important role in spermatogenesis by affecting the mitochondrial morphogenesis and individualization of sperms in D. melanogaster.