Project description:The piRNA pathway is studied in great detail in Drosophila female germline. In this study we show that unlike the female germline where all Piwi proteins are expressed throughout oogenesis, Ago3 - a Piwi family protein shows a spatial expression male germline. To understand dynamics of piRNA pathway during spermatogonia and primary spermatocyte stages of male germline development, we used arrest mutants. The bag of marbles (bam) and benign gonial cell neoplasm (bgcn) mutants have only early mitotic dividing germline cells in the testes due to failure to progress to primary spermatocyte stage, the cannonball (can) and spermatocyte arrest (sa) mutant germline cells cannot progress beyond primary spermatocyte stage. To investigate the dynamics of the piRNA pathway during spermatogenesis in spermatogonia and primary spermatocyte stages, we used testicular tissues from these stage-specific arrested mutants. While we used entire bam and bgcn mutant testes for spermatogonia purification, we while we manually removed the apical regions of can and sa mutant testes to exclude mitotically dividing undifferentiated germline cells for primary spermatocytes purification. Our results show that piRNAs mapping to transposons are more abundant in spermatogonia, whereas those mapping to Suppressor of Stellate [Su(Ste)] and AT-chX are mostly expressed in primary spermatocytes. Furthermore we observed that transposon-mapping piRNAs with ping-pong signature are more abundant in spermatogonia albeit still detectable in primary spermatocytes where Ago3 is not expressed. These results suggest that robust piRNA production via ping-pong cycle takes place in spermatogonia, and to a lesser extent in primary spermatocytes even in the absence of Ago3. Consistently, piRNAs from ago3 mutant testes also exhibit the ping-pong signature, confirming that a non-canonical ping-pong cycle is acting during spermatogenesis. Our study provides a developmental dimension to the piRNA pathway and uncovers a new mechanism used in the male germline to silence transposons.

Project description:The piRNA pathway is studied in great detail in Drosophila female germline. In this study we show that unlike the female germline where all Piwi proteins are expressed throughout oogenesis, Ago3 - a Piwi family protein shows a spatial expression male germline. To understand dynamics of piRNA pathway during spermatogonia and primary spermatocyte stages of male germline development, we used arrest mutants. The bag of marbles (bam) and benign gonial cell neoplasm (bgcn) mutants have only early mitotic dividing germline cells in the testes due to failure to progress to primary spermatocyte stage, the cannonball (can) and spermatocyte arrest (sa) mutant germline cells cannot progress beyond primary spermatocyte stage. To investigate the dynamics of the piRNA pathway during spermatogenesis in spermatogonia and primary spermatocyte stages, we used testicular tissues from these stage-specific arrested mutants. While we used entire bam and bgcn mutant testes for spermatogonia purification, we while we manually removed the apical regions of can and sa mutant testes to exclude mitotically dividing undifferentiated germline cells for primary spermatocytes purification. Our results show that piRNAs mapping to transposons are more abundant in spermatogonia, whereas those mapping to Suppressor of Stellate [Su(Ste)] and AT-chX are mostly expressed in primary spermatocytes. Furthermore we observed that transposon-mapping piRNAs with ping-pong signature are more abundant in spermatogonia albeit still detectable in primary spermatocytes where Ago3 is not expressed. These results suggest that robust piRNA production via ping-pong cycle takes place in spermatogonia, and to a lesser extent in primary spermatocytes even in the absence of Ago3. Consistently, piRNAs from ago3 mutant testes also exhibit the ping-pong signature, confirming that a non-canonical ping-pong cycle is acting during spermatogenesis. Our study provides a developmental dimension to the piRNA pathway and uncovers a new mechanism used in the male germline to silence transposons. The difference in piRNA from spermatogonia and primary spermatocyte stages was studied by comparing small RNAs from bam and bgcn mutant testis, which represent spermatogonia stages with the small RNAs from apex removed can and sa testis, representing primary spermatocyte stages. In the study we also studied effect of loss of Piwi family proteins Aub and Ago3, which have different spatial expression during male germline development.

Project description:Both transcription and post-transcriptional processes, such as alternative splicing, play crucial roles in controlling developmental programs in metazoans. Recently emerged RNA-seq method has brought our understanding of eukaryotic transcriptomes to a new level, because it can resolve both gene expression level and alternative splicing events simultaneously. To gain a better understanding of cellular differentiation in gonads, we analyzed mRNA profiles from Drosophila testes and ovaries using RNA-seq. We identified a set of genes that have sex-specific isoforms in wild-type (WT) gonads, including several transcription factors. We found that differentiation of sperms from undifferentiated germ cells induced a dramatic downregulation of RNA splicing factors. Our data confirmed that RNA splicing events are significantly more frequent in the undifferentiated cell-enriched bag of marbles (bam) mutant testis, but downregulated upon differentiation in WT testis. Consistent with this, we showed that genes required for meiosis and terminal differentiation in WT testis were mainly regulated at the transcriptional level, but not by alternative splicing. Unexpectedly, we observed an increase in expression of all families of chromatin remodeling factors and histone modifying enzymes in the undifferentiated cell-enriched bam testis. More interestingly, chromatin regulators and histone modifying enzymes with opposite enzymatic activities are coenriched in undifferentiated cells in testis, suggesting that these cells may possess dynamic chromatin architecture. Finally, our data revealed many new features of the Drosophila gonadal transcriptomes, and will lead to a more comprehensive understanding of how differential gene expression and splicing regulate gametogenesis in Drosophila. Our data provided a foundation for the systematic study of gene expression and alternative splicing in many interesting areas of germ cell biology in Drosophila, such as the molecular basis for sexual dimorphism and the regulation of the proliferation vs terminal differentiation programs in germline stem cell lineages. RNA-Seq experiments for four Drosophila melanogaster samples: (1) bam mutant testes, (2) wild-type testes, (3) bam mutant ovaries, (4) wild-type ovaries

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Drosophila melanogaster

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