The ETS transcription factor pointed is essential for germ line survival in "Drosophila melanogaster"

Résumé

Stem cells reside in a specialized microenvironment or niches that maintain them in an undifferentiated state and that regulate their proliferation. Drosophila ovarian germline stem cell niche shapes during larval development and is composed of support cells -often in contact with stem cells-, signaling molecules communicating the cells within the niche and the extracellular matrix. At these stages soma-germline interactions are critical to control the formation of the niche and to tightly regulate the proliferation of the primordial germ cells (PGC) to assure that every niche receives a supply of 2-3 Germline stem cells (GSCs). We have mapped and characterized a new mutation that prevents germline survival. Adult flies homozygous for the mutation are viable but sterile, as their reproductive system is agametic (absence of germ cells). Interestingly, because other somatic cell types proliferate normally when mutated, our mutation disrupts germline cells viability specifically. PGC development initiates properly as embryonic mutant gonads form organs of normal size and shape. However, at larval stages the number of PGCs is significantly reduced as they start dying by apoptosis. Thus, the somatic niche of the GSCs forms normally but devoid of germ cells. The agametic phenotype is due to a fortuitous mutation on the 3R arm chromosome. We have mapped the mutation to an intronic region near the 5¿UTR of the ETS transcription factor PointedC/E. We also demonstrate that Pnt regulates PGC survival non-autonomously, as it is expressed in the somatic cells of the niche and this expression rescues the agametic phenotype. Our results show for the first time that the pointed locus plays a major role in controlling the survival and proliferation of the PGCs and suggest that the balance in pnt isoforms is critical for this function.