Dataset Information

The hsp60B gene of Drosophila melanogaster is essential for the spermatid individualization process.

ABSTRACT: The 60-kDa heat shock protein family (Hsp60) is found in prokaryotes, mitochondria, and chloroplasts. The Hsp60 proteins promote proper protein folding by preventing aggregation. In Drosophila melanogaster, the hsp60 gene is essential for a variety of developmental processes, beginning at early embryogenesis. In this study we show that an additional member of the Drosophila hsp60 gene family, hsp60B, is essential in male fertility. In males homozygous for a mutation of the hsp60B gene, developmental processes appeared normal throughout most of spermatogenesis, including spermatocyte growth, meiosis, and spermatid elongation. At these stages, mitochondria also displayed a differentiation process similar to wild-types. However, we found that the mutation disrupted a late stage of spermatogenesis, the spermatid individualization process. In this process, the individualization complex is assembled at spermatid nuclear heads, traverses along spermatid tails, and generates membranes for each of the spermatids in a cyst. Our analysis further shows that the individualization complex in sterile males displayed abnormal morphology as it was traveling along the spermatid tails. The Drosophila Hsp60 proteins are believed to be exclusively localized in the mitochondria. Our observation that the hsp60B mutation displayed no apparent defect in mitochondrial differentiation during spermatogenesis suggests that the Hsp60B protein may operate in a nonmitochondrial location.

SUBMITTER: Timakov B

PROVIDER: S-EPMC434385 | biostudies-literature | 2001 Jan

REPOSITORIES: biostudies-literature

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The hsp60B gene of Drosophila melanogaster is essential for the spermatid individualization process.

Timakov B B Zhang P P

Cell stress & chaperones 20010101 1

The 60-kDa heat shock protein family (Hsp60) is found in prokaryotes, mitochondria, and chloroplasts. The Hsp60 proteins promote proper protein folding by preventing aggregation. In Drosophila melanogaster, the hsp60 gene is essential for a variety of developmental processes, beginning at early embryogenesis. In this study we show that an additional member of the Drosophila hsp60 gene family, hsp60B, is essential in male fertility. In males homozygous for a mutation of the hsp60B gene, developme ...[more]

PMID: 11525246

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Project description:Spermatogenesis in all animal species occurs within a syncytium. Only at the very end of spermatogenesis are individual sperm cells resolved from this syncytium in a process known as individualization. Individualization in Drosophila begins as a membrane-cytoskeletal complex known as the individualization complex (IC) assembles around the sperm heads and proceeds down the flagella, removing cytoplasm from between the sperm tails and shrink-wrapping each spermatid into its own plasma membrane as it travels. The mulet (mlt) mutation results in severely disrupted ICs, indicating that the mlt gene product is required for individualization. Inverse PCR followed by cycle sequencing maps all known P-insertion alleles of mlt to two overlapping genes, CG12214 (the Drosophila tubulin-binding cofactor E-like homolog) and KCNQ (a large voltage-gated potassium channel). However, since the alleles of mlt map to the 5'-UTR of CG12214 and since CG12214 is contained within an intron of KCNQ, it was hypothesized that mlt and CG12214 are allelic. Indeed, CG12214 mutant testes exhibited severely disrupted ICs and were indistinguishable from mlt mutant testes, thus further suggesting allelism. To test this hypothesis, alleles of mlt were crossed to CG12214 in order to generate trans-heterozygous males. Testes from all trans-heterozygous combinations revealed severely disrupted ICs and were also indistinguishable from mlt mutant testes, indicating that mlt and CG12214 fail to complement one another and are thus allelic. In addition, complementation testing against null alleles of KCNQ verified that the observed individualization defect is not caused by a disruption of KCNQ. Finally, since a population of spermatid-associated microtubules known to disappear prior to movement of the IC abnormally persists during individualization in CG12214 mutant testes, this work implicates TBCE-like in the removal of these microtubules prior to IC movement. Taken together, these results identify mlt as CG12214 and suggest that the removal of microtubules by TBCE-like is a necessary pre-requisite for proper coordinated movement of the IC.

Project description:Recent studies on nuclear-encoded mitochondrial genes (N-mt genes) in Drosophila melanogaster have shown a unique pattern of expression for newly duplicated N-mt genes, with many duplicates having a testis-biased expression and playing an essential role in spermatogenesis. In this study, we investigated a newly duplicated N-mt gene-i.e., Cytochrome c oxidase 4-like (COX4L)-in order to understand its function and, consequently, the reason behind its retention in the D. melanogaster genome. The COX4L gene is a duplicate of the Cytochrome c oxidase 4 (COX4) gene of OXPHOS complex IV. While the parental COX4 gene has been found in all eukaryotes, including single-cell eukaryotes such as yeast, we show that COX4L is only present in the Brachycera suborder of Diptera; thus, both genes are present in all Drosophila species, but have significantly different patterns of expression: COX4 is highly expressed in all tissues, while COX4L has a testis-specific expression. To understand the function of this new gene, we first knocked down its expression in the D. melanogaster germline using two different RNAi lines driven by the bam-Gal4 driver; second, we created a knockout strain for this gene using CRISPR-Cas9 technology. Our results showed that knockdown and knockout lines of COX4L produce partial sterility and complete sterility in males, respectively, where a lack of sperm individualization was observed in both cases. Male infertility was prevented by driving COX4L-HA in the germline, but not when driving COX4-HA. In addition, ectopic expression of COX4L in the soma caused embryonic lethality, while overexpression in the germline led to a reduction in male fertility. COX4L-KO mitochondria show reduced membrane potential, providing a plausible explanation for the male sterility observed in these flies. This prominent loss-of-function phenotype, along with its testis-biased expression and its presence in the Drosophila sperm proteome, suggests that COX4L is a paralogous, specialized gene that is assembled in OXPHOS complex IV of male germline cells and/or sperm mitochondria.

Dataset Information

The hsp60B gene of Drosophila melanogaster is essential for the spermatid individualization process.

Publications

The hsp60B gene of Drosophila melanogaster is essential for the spermatid individualization process.

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