C. elegansEVI1 proto-oncogene, EGL-43, is necessary for Notch-mediated cell fate specification and regulates cell invasion

Abstract

During C. elegans development, LIN-12 (Notch) signaling specifies the anchor cell (AC) and ventral uterine precursor cell (VU) fates from two equivalent pre-AC/pre-VU cells in the hermaphrodite gonad. Once specified, the AC induces patterned proliferation of vulva via expression of LIN-3 (EGF) and then invades into the vulval epithelium. Although these cellular processes are essential for the proper organogenesis of vulva and appear to be temporally regulated, the mechanisms that coordinate the processes are not well understood. We computationally identified egl-43 as a gene likely to be expressed in the pre-AC/pre-VU cells and the AC, based on the presence of an enhancer element similar to the one that transcribes lin-3 in the same cells. Genetic epistasis analyses reveal that egl-43 acts downstream of or parallel to lin-12 in AC/VU cell fate specification at an early developmental stage, and functions downstream of fos-1 as well as upstream of zmp-1 and him-4 to regulate AC invasion at a later developmental stage. Characterization of the egl-43regulatory region suggests that EGL-43 is a direct target of LIN-12 and HLH-2(E12/47), which is required for the specification of the VU fate during AC/VU specification. EGL-43 also regulates basement membrane breakdown during AC invasion through a FOS-1-responsive regulatory element that drives EGL-43 expression in the AC and VU cells at the later stage. Thus, egl-43integrates temporally distinct upstream regulatory events and helps program cell fate specification and cell invasion.

LIN-12/Notch Regulates lag-1 and lin-12 Expression during Anchor Cell/Ventral Uterine Precursor Cell Fate Specification

“…Vulval induction, AC invasion, and vulva-uterine connection analysis Vulval induction, anchor cell invasion, and vulval uterine connection were assayed as described previously (Hill and Sternberg, 1992;Hwang et al, 2007;Sherwood and Sternberg, 2003). In a wild-type hermaphrodite, three of the six VPCs adopt 1° and 2° cell fates to divide into 22 descendents during L3, which was measured in the transgenic lines expressing lag-1 cDNA in the AC from the AC-specific cdh-3 promoter (Kirouac and Sternberg, 2003).…”

“…This element is also expressed in the VU cells and their descendents as a downstream of the transcription factor FOS-1. Another element supports egl-43 expression in the AC when vulval-uterine connection takes place at early L4 stage (Hwang et al, 2007).…”

“…A genome-wide computational search to identify genes coexpressed from a common regulatory element identified egl-43 as a gene co-expressed with lin-3 during AC/VU specification as well as a LIN-12 downstream target (Hwang and Sternberg, 2004;Hwang et al, 2007). Here, an enhancer element (anchor cell element of lin-3, ACEL) in both lin-3 and egl-43 was sufficient to activate these genes in pre-AC/pre-VU cells and the AC, but not in VU cells.…”

“…Thus, a similar element could activate lag-2 transcription during AC/VU specification. Expression of egl-43 appears to be regulated by several distinct regulatory elements during AC/VU specification and later cellular processes that involve the AC and VU cells (Hwang et al, 2007). In addition to ACEL, an element that involves clustered LAG-1 binding sites supports egl-43 expression in VU cells immediately after AC/VU specification.…”

“…In previous experiments to dissect the egl-43 regulatory elements, the role of a regulatory element that contains clustered LAG-1 binding sites was not clear due to the presence of an ACEL element that strongly supports gene expression during AC/VU specification (Hwang et al, 2007). Here, in an attempt to study the role of regulatory elements containing clustered LAG-1 binding sites, we addressed whether clustered LAG-1 binding sites in lag-1 and lin-12 are involved in the expression of these genes during AC/VU specification.…”