Multiple in Vivo Biological Processes Are Mediated by Functionally Redundant Activities of Drosophila mir-279 and mir-996

While most mirna knockouts exhibit only subtle defects,a handful of mirnas are profoundly required for development or physiology. a particularly compelling locus is drosophila mir-279,which was reported as essential to restrict the emergence of co2-sensing neurons,to maintain circadian rhythm,and to regulate ovarian border cells. the mir-996 locus is located near mir-279 and bears a similar seed,but they otherwise have distinct,conserved,non-seed sequences,suggesting their evolutionary maintenance for separate functions. we generated single and double deletion mutants of the mir-279 and mir-996 hairpins,and cursory analysis suggested that mir-996 was dispensable. however,discrepancies in the strength of individual mir-279 deletion alleles led us to uncover that all extant mir-279 mutants are deficient for mature mir-996,even though they retain its genomic locus. we therefore engineered a panel of genomic rescue transgenes into the double deletion background,allowing a pure assessment of mir-279 and mir-996 requirements. surprisingly,detailed analyses of viability,olfactory neuron specification,and circadian rhythm indicate that mir-279 is completely dispensable. instead,an endogenous supply of either mir-279 or mir-996 suffices for normal development and behavior. sensor tests of nine key mir-279/996 targets showed their similar regulatory capacities,although transgenic gain-of-function experiments indicate partially distinct activities of these mirnas that may underlie that co-maintenance in genomes. altogether,we elucidate the unexpected genetics of this critical mirna operon,and provide a foundation for their further study. more importantly,these studies demonstrate that multiple,vital,loss-of-function phenotypes can be rescued by endogenous expression of divergent seed family members,highlighting the importance of this mirna region for in vivo function. © 2015 sun et al.