What happens in embryos lacking PAL-1 function?
PAL-1 is Caudal-like homeodomain transcription factor maternally deposited posteriorly via post-transcriptional control by MEX-3 RNA-binding protein, MEX-5/6 and SPN-4 regulating translation efficiency. It activates posterior program genes including tbx-8/9 T-box and elt-3 in EMS descendants C and D blastomeres producing body wall muscle, hypodermis, intestine-associated muscle. C blastomere generates hypodermis and muscle, D generates muscle only. In pal-1 mutants or RNAi knockdown, posterior blastomeres transform to anterior-like EMS fates, lacking muscle myosin MYO-3 and COL cuticle markers, causing embryonic arrest with absent C and D lineages.
Ref: Hunter & Kenyon, Cell 1996: PAL-1 Caudal homolog required for C and D blastomere specification.