The role of Groucho proteins and repression in Wnt polarized asymmetric cell division in C. elegans
Creators: name: Bekas, Kimberly N
Publisher: name: University of Iowa
Year: 2022
Subjects: asymmetric cell division
C. elegans
Groucho
LSY-22
UNC-37
Wnt
public abstract

description: Asymmetric cell division (ACD) is a fundamental mechanism of developmental cell fate specification and adult tissue homeostasis. ACD is important for generating and maintaining tissue diversity throughout an organism’s life. During ACD, a dividing mother cell starts to partition important cellular factors to either dividing resulting in a division with two daughter cells that are different from one another. In C. elegans, the Wnt/β-catenin asymmetry (WβA) pathway regulates ACDs throughout embryonic and larval development. Under control of Wnt ligand-induced polarity, the transcription factor TCF functions with the coactivator β-catenin to activate gene expression in the signaled cell. In absence of the coactivator, the critical transcription factor TCF remains in the nucleus where Wnt target genes are repressed in the nascent unsignaled daughter cell. While the mechanism of activation in the signaled daughter cell are well understood, the proteins involved in target gene repression in the unsignaled daughter cell have yet to be elucidated. To date, the Groucho family of corepressors have been shown to function in canonical Wnt signaling, yet investigation into the contribution of Groucho-mediated repression in WβA is lacking. Further, the function of the C. elegans short Groucho amino enhancer of split (AES) homolog, lsy-22/AES has only been evaluated in neuronal cell fate decisions and investigation of LSY-22/AES function in Wnt signaling has not been investigated. Further, conflicting evidence exists demonstrating Groucho-mediated repression may be either aided or repressed by addition of AES subfamily. Here we demonstrate a genetic interaction between the C. elegans Groucho repressors, UNC-37/Groucho and LSY-22/AES, with POP-1/TCF in three C. elegans ACDs: the distal tip cells (DTCs), the seam cell (SCs) and the embryonic endoderm. In the DTC lineage, we observed fate increases in the signaled cell fate after individual and double Groucho loss of function, representing the first demonstration of Groucho function in wildtype WβA regulated ACD. Notably, we demonstrate enhanced DTC gains in the unc-37/Groucho null subjected to lsy-22/AES(RNAi), suggesting a function of a lsy-22/AES homorepressive complex. Further, ectopic WβA transgene expression occurs more frequently than DTC fate changes, suggesting derepression generates an intermediate cell fate. In the SCs, loss of unc-37/Groucho or lsy-22/AES in a pop-1/tcf(RNAi) hypomorphic background enhances a POP-1/TCF seam cell expansion and target gene misregulation. Moreover, a surprising SC decrease occurs in unc-37/Groucho nulls subjected to POP-1/TCF depletion. This phenotype may be due to UNC-37/Groucho regulation of pop-1/tcf since we find increased POP-1/TCF in the SCs of unc-37/Groucho nulls. Evaluation of individual and double Groucho nulls indicate unc-37/Groucho and lsy-22/AES maybe maternally inherited. As such, we established Groucho functions in embryonic endoderm development in a histone deacetylase, HDA-1, compromised background. Together, these data indicate Groucho-mediated repression is widespread in WβA ACDs and suggests a novel role of LSY-22/AES as a bona fide POP-1/TCF repressor. Thus, our research expands the understanding of Groucho-mediated repression, WβA regulated cell divisions and LSY-22/AES function.