Practice question

SKN-1 is maternally deposited transcription factor required for EMS blastomere descendant fates. In skn-1 null or strong loss-of-function embryos generated by RNAi, transcriptional activation of med-1, med-2 fails, so cascade leading to end-1, end-3, tbx-35, ceh-51 not induced. EMS produces daughters that do not form pharynx mesoderm from MS or intestine from E, instead adopts C-like muscle fate producing excess body wall muscle, while overall embryo arrests. Hence loss of EMS-derived lineages including intestinal, pharyngeal and body wall muscle subsets normally sourced from MS and E leads to failure of gut formation and embryonic lethality with phenotype lacking endoderm.