lep-5: a long noncoding RNA is a novel heterochronic regulator in C. elegans

Abstract

Thesis (Ph.D.)--University of Rochester. School of Medicine & Dentistry. Dept. of Biomedical Genetics, 2014.A fundamental question in developmental biology is how the temporal aspect of development is controlled. Research in the nematode C. elegans has revealed a set of conserved genetic factors, the so called "heterochronic" genes, that function in a temporal cascade to regulate the temporal identity of a cell and the timing of stage specific events in the worm. In this study, we utilize the morphogenesis of the C. elegans male tail as a unique setting to be able to identify novel heterochronic genes that control late larval development. Through the use of forward genetic screens, we have isolated lep-5, a mutant that disrupts the timing of male tail morphogenesis. We showed that lep-5 controls the timing of tail tip retraction through regulating the temporal expression of dmd-3, a master regulator of tail tip retraction. We confirmed that lep-5 is a novel heterochronic regulator in C. elegans and used epistasis experiments to place lep-5 into the pathway controlling the timing of male tail morphogenesis upstream of known heterochronic genes such as lin-41 and let-7. We found that in addition to regulating tail tip retraction, lep-5 also controls other aspects of the larval to adult transitions such as the cessation of molting. We revealed a role for lep-5 and other members of the heterochronic pathway in regulating the changes in nervous system gene expression and behavior that occur as C. elegans transitions from larva to adult. Finally, we identified the gene disrupted in the mutant as H36L18.2, and found that lep-5 functions not as a protein but instead as a novel long non-coding RNA. Through structure function experiments, we identified portions of the transcript necessary for lep-5 function. This work has identified a novel heterochronic regulator in C. elegans and suggests a new role for long noncoding RNAs in both development and temporal regulation