Abstract
Stem cell maintenance requires expression of genes essential for stemness and repression of differentiation genes. How this is achieved remains incompletely understood. Here we investigate the requirement for central components of heterochromatin, Heterochromatin Protein 1 (HP1) and the histone H3 lys9 methyltransferase Su(var)3-9, in the Drosophila male germline stem cell (GSC) self-renewal, a paradigm for studying adult stem cell behavior. We found that mutations or RNAi knock down of HP1 or Su(var)3-9 cause loss of GSCs, accompanied by defects in cell division or survival and premature expression of the differentiation gene bag of marbles (bam). Conversely, over-expressing HP1 increases GSC number in wildtype flies and, strikingly, restores fertility to the sterile hopscotch (hop) mutant flies that lack niche signals. These results suggest that the central components of heterochromatin play roles including repressing differentiation genes in Drosophila male GSC maintenance.
Highlights
Through four synchronous mitotic divisions, resulting in 16 spermatocytes
Our results indicate that both Heterochromatin Protein 1 (HP1) or Su(var)[3,4,5,6,7,8,9] are important for germline stem cell (GSC) self-renewal and for repressing differentiation genes, such as bam of marbles, they may play general roles such as cell division and survival
Our results suggest that proper heterochromatin formation might have a specific role in epigenetically repressing the expression of differentiation genes in GSCs, which is important for maintaining their self-renewal
Summary
Through four synchronous mitotic divisions, resulting in 16 spermatocytes. Without JAK/STAT signaling, GSCs differentiate but do not self-renew, while ectopic JAK/STAT signaling greatly expands the stem cell population[15,16]. Further studies have indicated that JAK/STAT signaling primarily regulates self-renewal of somatic CySCs, which are essential for GSC self-renewal[17,18]. Despite these findings, the precise mechanisms controlling stem cell self-renewal remain incompletely understood. Our results indicate that both HP1 or Su(var)[3,4,5,6,7,8,9] are important for GSC self-renewal and for repressing differentiation genes, such as bam of marbles (bam), they may play general roles such as cell division and survival. Our results suggest that proper heterochromatin formation might have a specific role in epigenetically repressing the expression of differentiation genes in GSCs, which is important for maintaining their self-renewal
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