Adult somatic stem cells in Drosophila melanogaster actively maintain their sexual identity, a new study published in Developmental Cell finds.
Sex maintenance has been shown to occur in the adult mammalian testis and ovary, but whether this phenomenon is present in fruitflies was unknown. By screening phenotypes, Ma et al. identified a spontaneous mutation that caused the appearance of cells resembling ovarian follicle cells throughout the adult testis as the organism aged. Genetic complementation and rescue experiments localized this mutation to the regulatory region of the chinmo gene, which encodes the essential cell-fate determinant Chronologically inappropriate morphogenesis (Chinmo), a target of the Jak-STAT signalling pathway.
“sperm-producing germ cells were also arrested at an early stage”
Reduced expression of Chinmo in adult testes caused somatic stem cells — cyst stem cells (CySCs) — to transdifferentiate into cells resembling multipotent female follicle stem cells, as confirmed by cell type-specific RNA interference (RNAi) knockdown of chinmo. Sperm-producing germ cells were also arrested at an early stage.
Chinmo was shown to act through the canonical sex determinant DoublesexM (DsxM) to maintain the male identity of adult CySCs. The authors posit that “Chinmo promotes expression of DsxM, which in turn regulates its own set of target genes that are critical for male sex identity”. Given that re-establishing DsxM expression is insufficient to rescue the phenotype, Chinmo probably affects the expression of DsxM-independent target genes that are required for CySC self-renewal.
This study represents another step to unravelling the process of transdifferentiation of stem cells at the mechanistic level.
Ma, Q. et al. The Jak-STAT target Chinmo prevents sex transformation of adult stem cells in the Drosophila testis niche. Dev. Cell http://dx.doi.org/10.1016/j.devcel.2014.10.004 (2014)