Heat shock cognate 70 genes contribute to Drosophila spermatocyte growth progression possibly through the insulin signaling pathway

Abstract

Drosophila spermatocytes grow up to 25 times their original volume before the onset of male meiosis. Several insulin‐like peptides and their cognate receptors (InR) are essential for the cell growth process in Drosophila. Here, we aimed to identify additional signaling pathways and other regulatory factors required for germline cell growth in Drosophila males. Spermatocyte‐specific expression of the dominant‐negative form of InR inhibits cell growth. Conversely, constitutively active forms of signaling factors downstream of InR suppress growth inhibition. Furthermore, hypomorphic mutations in the target of rapamycin (Tor) inhibit spermatocyte growth. These data indicate that the insulin/TOR pathway is essential for the growth of premeiotic spermatocytes. RNA interference (RNAi) screening for the identification of other novel genes associated with cell growth showed that the silencing of each of the five members of heat shock cognate 70 (Hsc70) genes significantly inhibited the process. Hsc70‐silenced spermatocytes showed Akt inhibition downstream of the insulin signaling pathway. Our pleckstrin homology domain‐​green fluorescent protein (PH‐GFP) reporter studies indicated that PI3K remained activated in Hsc70‐4‐silenced cells, suggesting that the Hsc70‐4 protein possibly targets Akt or Pdk1 acting downstream of PI3K. Moreover, each of the Hsc70 proteins showed different subcellular localizations. Hsc70‐2 exhibited cytoplasmic colocalization with Akt in spermatocytes before nuclear entry of the kinase during the growth phase. These results indicated the involvement of Hsc70 proteins in the activation of various steps in the insulin signaling pathway, which is essential for spermatocyte growth. Our findings provide insights into the mechanism(s) that enhance signal transduction to stimulate the growth of Drosophila spermatocytes.

VCP acts downstream of tTAFs to downregulate mono-ubiquitinated H2A and promote spermatocyte differentiation inDrosophila

“…Like VCP and sa , multiple of the de-repressed genes, including hsc70-2 and ubi-p63e , are required for meiotic progression (Azuma, et al, 2021; Lu, et al, 2013). We therefore hypothesized that genetically inhibiting H2Aub may rescue some aspects of germ-cell development in VCP -RNAi testes.…”

Biochemical Characterization and Functional Analysis of Glucose Regulated Protein 78 from the Silkworm Bombyx mori

“…As a highly conserved ER resident protein, GRP78 is involved in the folding and assembly of nascent proteins, serving as a master regulator of ER stress responses, facilitating cancer cell growth and viral replication [ 8 , 9 , 22 ]. GRP78 has been extensively studied in mammals [ 8 ], Drosophila [ 23 ], and fish [ 24 ]. However, the information regarding its molecular function in insect species is scarce.…”

“…The BmGRP78 exhibited a ubiquitous expression profile in different developmental stages and various tissues of B. mori , with the L4D3 stage and the gonad showing the highest transcription level. The evidence suggests that the GRP78 protein is an essential regulator of developmental processes in insects, and the mechanism of regulation may vary among different life stages and insect species [ 23 , 26 ]. GRP78 is reportedly associated with male reproduction, is expressed on the surface of human and rat sperm, and is associated with calcium-binding protein [ 27 ].…”

Comparative Ubiquitome Analysis Reveals Deubiquitinating Effects Induced by Wolbachia Infection in Drosophila melanogaster

“…Knockdown of Hsc70-4 resulted in fly testes full of small undifferentiated germ cells [ 44 ]. Recent studies suggested that Hsc70-4 possibly targeted Akt or Pdk1 acting downstream of PI3K, thus regulating spermatocyte growth and meiosis initiation [ 57 ]. Therefore, the dramatic reduction of ubiquitinated Hsc70-4 by Wolbachia infection might damage germ cell differentiation in Drosophila testes.…”