Knockdown of SKN-1 and the Wnt effector TCF/POP-1 reveals differences in endomesoderm specification in C. briggsae as compared with C. elegans

Abstract

In the nematode, C. elegans, the bZIP/homeodomain transcription factor SKN-1 and the Wnt effector TCF/POP-1 are central to the maternal specification of the endomesoderm prior to gastrulation. The 8-cell stage blastomere MS is primarily a mesodermal precursor, giving rise to cells of the pharynx and body muscle among others, while its sister E clonally generates the entire endoderm (gut). In C. elegans, loss of SKN-1 results in the absence of MS-derived tissues all of the time, and loss of gut most of the time, while loss of POP-1 results in a mis-specification of MS as an E-like cell, resulting in ectopic gut. We show that in C. briggsae, RNAi of skn-1 results in a stronger E defect but no apparent MS defect, while RNAi of pop-1 results in loss of gut and an apparent E to MS transformation, the opposite of the pop-1 knockdown phenotype seen in C. elegans. The difference in pop-1(−) phenotypes correlates with changes in how the endogenous endoderm-specifying end genes are regulated by POP-1 in the two species. Our results suggest that integration of Wnt-dependent and Wnt-independent cell fate specification pathways within the Caenorhabditis genus can occur in different ways.

New Tools for Investigating the Comparative Biology of Caenorhabditis briggsae and C. elegans

“…With this ability we created strains that allow the ready determination of the C. briggsae embryonic cell lineage and in turn the high-resolution mapping of gene expression. Using transgenes as fate markers, we used RNAi and automated lineaging to study the effects of cbr-pop-1 loss of function on cell fates, confirming and extending the recent results (Lin et al 2009). …”

“…In addition, the expression reporters we have generated also provide markers for cell fate. To evaluate the utility of automated lineaging combined with cell fate markers in C. briggsae we investigated the recent report that reduction of the activity of a Wnt signaling pathway TCF-like effector, pop-1, by RNAi produced the opposite homeotic lineage transformation between E and MS in C. briggsae to that produced in C. elegans (Lin et al 2009). We confirmed the results by parallel application of the lineaging technology to the two species; i.e., RNAi against pop-1 produced homeotic transformation from MS to E in C. elegans but from E to MS in C. briggsae ( Figure 6).…”

The NK-2 class homeodomain factor CEH-51 and the T-box factor TBX-35 have overlapping function inC. elegansmesoderm development

“…(n754) . We have previously observed a lack of strict additivity and variability in the number of cells expressing tissuespecific reporters (Lin et al, 2009). We attribute this primarily to expression mosaicism between animals and the difficulty of resolving adjacent cells.…”

“…Laser ablations were performed as described (Lin et al, 2009). Animals were imaged on a Zeiss Axioplan using a Hamamatsu ORCA II digital camera, or on an Olympus BX-61 with a Canon 350D camera.…”

-Catenin-Dependent Wnt Signaling in C. elegans: Teaching an Old Dog a New Trick

“…Here we summarize our current understanding of these two C. elegans signaling pathways and the ways they are similar to, and diverge from, Wnt signaling pathways in other species. Although recent work has extended our knowledge of Wnt signaling to other nematode species (Zheng et al 2005;Rudel et al 2008;Tian et al 2008;Lin et al 2009;Owraghi et al 2010;Seetharaman et al 2010;Penigault and Felix 2011a;Wang and Sommer 2011), in this review we will concern ourselves with a survey of Wnt signaling in the established model system C. elegans.…”