unc-37/Groucho and lsy-22/AES repress Wnt target genes in C. elegans asymmetric cell divisions

Abstract

Asymmetric cell division (ACD) is a fundamental mechanism of developmental cell fate specification and adult tissue homeostasis. In C. elegans, the Wnt/beta-catenin asymmetry (WβA) pathway regulates ACDs throughout embryonic and larval development. Under control of Wnt ligand-induced polarity, the transcription factor TCF/POP-1 functions with the coactivator beta-catenin/SYS-1 to activate gene expression in the signaled cell or, in absence of the coactivator, to repress Wnt target genes in the nascent unsignaled daughter cell. To date, a broad investigation of Groucho function in WβA is lacking and the function of the short Groucho AES homolog, lsy-22 has only been evaluated in C. elegans neuronal cell fate decisions. Further, there is conflicting evidence showing TCF utilizing Groucho-mediated repression may be either aided or repressed by addition of AES subfamily of Groucho proteins. Here we demonstrate a genetic interaction between Groucho repressors and TCF/POP-1 in ACDs in the somatic gonad, the seam hypodermal stem cell lineage and the early embryo. Specifically, in the somatic gonad lineage, the signaled cell fate increases after individual and double Groucho loss of function, representing the first demonstration of Groucho function in wild-type WβA ACD. Further, WβA target gene misexpression occurs at a higher rate than DTC fate changes, suggesting derepression generates an intermediate cell fate. In seam cell ACD, loss of Groucho unc-37 or Groucho-like lsy-22 in a pop-1(RNAi) hypomorphic background enhances a pop-1 seam cell expansion and target gene misregulation. Moreover, while POP-1 depletion in lsy-22 null mutants yielded an expected increase in seam cells we observed a surprising seam cell decrease in the unc-37 null subjected to POP-1 depletion. This phenotype may be due to UNC-37 regulation of pop-1 expression in this tissue since we find misregulation of POP-1 in unc-37 mutants. Lastly, Groucho functions in embryonic endoderm development since we observe ectopic endoderm target gene expression in lsy-22(ot244) heterozygotes and unc-37(tm4649) heterozygotes subjected to intermediate levels of hda-1(RNAi). Together, these data indicate Groucho repressor modulation of cell fate via regulation of POP-1/TCF repression is widespread in asymmetric cell fate decisions and suggests a novel role of LSY-22 as a bona fide TCF repressor. As AES Grouchos are well-conserved, our model of combinatorial TCF repression by both Gro/TLE and AES warrants further investigation.

Dynamic compartmentalization of the pro-invasive transcription factor NHR-67 reveals a role for Groucho in regulating a proliferative-invasive cellular switch inC. elegans

“…Our proposed model of POP-1 acting as a repressor in the proximal gonad is consistent with the finding that SYS-1 (β-catenin) expression is restricted to the distal gonad early in somatic gonad development and is not detectable in the AC or VU cells (Figure 5–figure supplement 3C) (Phillips et al, 2007; Sallee et al, 2015). It is also supported by recent evidence suggesting that UNC-37/LSY-22 mutant alleles phenocopy pop-1 knockdown, which produces ectopic distal tip cells (Bekas and Phillips, 2022).…”

EFL-3/E2F7 modulates Wnt signalling through repressing the LIT-1 Nemo-like kinase during asymmetric epidermal cell division inCaenorhabditis elegans

“…LIT-1 accumulation in the nucleus of posterior daughter cells is predicted to cause POP-1 nuclear export, thereby ensuring an optimal β-catenin (SYS-1) / POP-1 ratio in the nucleus that is conductive to Wnt target activation 20,[28][29][30] . Low LIT-1 levels in the nuclei of anterior daughter cells allow POP-1 to also remain at high levels in the nucleus and associate with proteins repressing Wnt target genes 30,32 . We therefore asked whether higher LIT-1 levels in efl-3 mutant nuclei have a consequence on POP-1 localisation.…”

“…Low POP-1 and high SYS-1 levels in posterior daughter nuclei allow the formation of a TCF/b-catenin transcriptional activator complex (POP-1/SYS-1) that activates Wnt targets 13,[28][29][30] , such as the GATA transcription factor EGL-18 31 . In anterior daughter cells, high POP-1 and low SYS-1 levels in the nucleus lead to recruitment of corepressors and transcriptional repression of Wnt targets 30,32 . Besides Wnt signalling, seam cell patterning is also regulated by other conserved transcription factors, such as a Runx/CBFb module, CEH-16/engrailed and various GATA factors, which can influence the decision between stem cell fate maintenance or differentiation [33][34][35][36][37][38][39] The E2F family of transcription factors (E2F1-8 in humans) controls gene expression during the cell cycle.…”