The
let-7 microRNA (miRNA) is an important regulator of developmental timing in the heterochronic pathway in the seam cell lineage of C. elegans. It is also a key regulator of cell differentiation in various organisms, and the loss of
let-7 expression has also been associated with human cancer [1]. In C. elegans,
let-7 controls cell division and terminal differentiation at the transition from the fourth larval stage (L4) to adult stage. Known targets of the
let-7 miRNA include
lin-41 and
hbl-1 genes, which are regulated via the interaction of their 3'UTRs with
let-7.
Even though these two targets of
let-7 have already been identified, it is still unclear how the functions of these genes give rise to the observed phenotypes. In order to understand how these key regulators of developmental timing actually effect cell fate outcomes, we aimed to identify additional downstream targets and effector genes. Loss of ACE (angiotensin converting enzyme)-like Non-peptidase (
acn-1) function lead to a suppression of the retarded phenotypes resulting from the loss of
let-7 expression, both in the hypodermal seam cells and in the vulva. However, loss of
acn-1 by itself did not appear to cause any precocious heterochronic defect in the seam cells and alae. Previous research has examined the expression pattern of
acn-1 and found that it is expressed in hypodermal seam cells, vulval cells, and the ray papillae of the male tail during all larval stages, but not in adulthood [2], meaning that it is down-regulated during the L4 or young adult stage, approximately the same time that
let-7 is being expressed. However, its 3'UTR does not have any predicted binding site for the
let-7 miRNA, making it unlikely to be a direct target of
let-7. Brooks et al. also reported that knock-down of
nhr-25, which is part of the nuclear hormone receptor protein family, by RNAi can silence the expression of ACN-1::GFP fusion protein expression in the seam cells [2]. This nuclear receptor gene
nhr-25 was later identified by our lab to play multiple roles at the larva-to-adult transition [3]. Our hypotheses is that
acn-1 is not directly regulated by
let-7, but functions further downstream. We aim to further elucidate how this new gene fits into the heterochronic pathway.
References: 1. Nimmo, R. and F. Slack, Chromosoma, 2009. 118(4).
2. Brooks, D.R., et al., J Biol Chem., 2003. 278(52).
3. Hada, K., et al., Dev Biol., 2010. 344(2).