Dual Mechanisms Implemented by LIN-28 for Positive Regulation OF HBL-1 Are Necessary for Proper Development of Distinct Tissues in Caenorhabditis elegans
In Caenorhabditis elegans, the heterochronic pathway is comprised of a hierarchy of genes that control the proper timing of developmental events. hbl-1 (Hunchback Like-1) encodes an Ikaros family zinc-finger transcription factor that promotes the L2 stage cell fate events of the hypodermis. The downregulation ofhbl-1 is a crucial step for the transition from the L2 to the L3 stage. There are two known processes through which negative regulation of hbl-1 occurs: suppression of hbl-1 expression by 3 let-7 miRNAs through the hbl-1 3’UTR and inhibition of HBL-1 activity by LIN-46. The mechanisms by which hbl-1 is positively regulated have not yet been full defined. Currently, this positive regulation seems to be the responsibility of the conserved developmental regulator lin-28. lin-28 is purported to oppose the activities of the 3 let-7 miRNAs and the Caenorhabditis specific heterochronic gene lin-46. Here I demonstrate the removal of 3 let-7 miRNA binding sites in 3’UTR of hbl-1 does not abolish negative regulation of hbl-1 in seam cells. I find lin-28 negatively regulates lin-46 expression by direct binding of the 5’UTR of lin-46. I report a novel sterilely phenotype due to the loss of HBL-1 activity in postembryonic development. Due to the increased sensitivity of the somatic gonad to HBL-1 protein levels, I utilize the development of this tissue as an alternate means to study the genetic relationships between lin-28, lin-46 and hbl-1. My results suggest lin-28 acts through a branched pathway, partially bypassing lin-46 to positively regulate hbl-1 either through its 3’UTR or by targeting a third unknown factor
