Abstract
BackgroundCaenorhabditis elegans seam cells serve as a good model to understand how genes and signaling pathways interact to control asymmetric cell fates. The stage-specific pattern of seam cell division is coordinated by a genetic network that includes WNT asymmetry pathway components WRM-1, LIT-1, and POP-1, as well as heterochronic microRNAs (miRNAs) and their downstream targets. Mutations in pry-1, a negative regulator of WNT signaling that belongs to the Axin family, were shown to cause seam cell defects; however, the mechanism of PRY-1 action and its interactions with miRNAs remain unclear.ResultsWe found that pry-1 mutants in C. elegans exhibit seam cell, cuticle, and alae defects. To examine this further, a miRNA transcriptome analysis was carried out, which showed that let-7 (miR-48, miR-84, miR-241) and lin-4 (lin-4, miR-237) family members were upregulated in the absence of pry-1 function. Similar phenotypes and patterns of miRNA overexpression were also observed in C. briggsae pry-1 mutants, a species that is closely related to C. elegans. RNA interference-mediated silencing of wrm-1 and lit-1 in the C. elegans pry-1 mutants rescued the seam cell defect, whereas pop-1 silencing enhanced the phenotype, suggesting that all three proteins are likely important for PRY-1 function in seam cells. We also found that these miRNAs were overexpressed in pop-1 hypomorphic animals, suggesting that PRY-1 may be required for POP-1-mediated miRNA suppression. Analysis of the let-7 and lin-4-family heterochronic targets, lin-28 and hbl-1, showed that both genes were significantly downregulated in pry-1 mutants, and furthermore, lin-28 silencing reduced the number of seam cells in mutant animals.ConclusionsOur results show that PRY-1 plays a conserved role to maintain normal expression of heterochronic miRNAs in nematodes. Furthermore, we demonstrated that PRY-1 acts upstream of the WNT asymmetry pathway components WRM-1, LIT-1, and POP-1, and miRNA target genes in seam cell development.
Highlights
Caenorhabditis elegans seam cells serve as a good model to understand how genes and signaling pathways interact to control asymmetric cell fates
Mutations in pry-1 lead to somatic defects. (a) Cuticle is weaker as demonstrated by the cuticle break assay. (b, c) pry-1 mutants having defective alae formation. (b) Control N2 animals have distinct rows of alae. pry1(mu38) mutants have defect with frequent breaks. (c) Quantification of alae defect in control N2 and pry-1(mu38) animals. (d-f) Heterochronic phenotypes in C. briggsae AF16 and Cbr-pry-1 mutants. (d) Alae defects are visible in Cbr-pry-1(sy5353). (e, f) Seam cells in control AF16 (e) and Cbr-pry1(sy5353) (f) are visualized by adherens-junction-associated marker Cel-dlg-1p::GFP
The phenotypic analysis of C. briggsae pry1 mutants, Cbr-pry-1(sy5353) [24], revealed similar gaps in alae as well as defective seam cell morphologies (Fig. 2d-f). Given these hypodermis-associated phenotypes, we investigated the role of pry-1 in seam cell development
Summary
Caenorhabditis elegans seam cells serve as a good model to understand how genes and signaling pathways interact to control asymmetric cell fates. Caenorhabditis elegans hypodermal seam cells serve as a good model to elucidate spatiotemporal patterns of division and differentiation that enable cells to adopt sex-specific fates. They comprise two lateral rows of multipotent somatic cells which extend from the anterior to the posterior of the nematode (Fig. 1), and that divide in a stem cell-like manner to both self-renew, and generate daughter hypodermal, neuronal, and neuronal-support cells [1]. Multiple genes and pathways have been shown to regulate seam cell division and differentiation These include the lin-4 (lin-4 and miR-237) and let-7 (let-7, miR-48, miR84, and miR-241) families of heterochronic microRNAs (miRNAs) that regulate the relative timing of developmental events [3,4,5,6,7]. Mutations in lin-4, miR-48, miR84, and miR-241 cause cells to reiterate stages, which affects both the number of differentiated seam cells, and cuticle development [9]
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