We previously showed that
vab-7 encodes a homeodomain protein of the even-skipped family that patterns posterior muscle and epidermal tissues. To find additional genes implicated in patterning, we screened for enhancers of a weak
vab-7 allele. One of the enhancers isolated,
we3 , is a new allele of the gene
egl-27 . Like previously isolated alleles of
egl-27 ,
egl-27 (
we3 ) mutants have defects in egg laying, phasmid dye filling and male tail morphology. However
egl-27 (
we3 ) additionally have defects in the organisation of muscle and epidermal cells during embryogenesis. Genetic and molecular data suggest that
egl-27 (
we3 ) may be a null allele of the locus. We cloned
egl-27 and found that it is similar to MTA1, a human gene with elevated expression in metastatic carcinomas. Sequence analysis of the predicted EGL-27 protein identified four conserved domains: a GATA like zinc finger domain, a myb-like DNA binding domain and two newly defined domains ELM1 and ELM2, for "EGL-27 and MTA1 homology". MTA1 has recently been shown to be a component of a protein complex with histone deacetylase and nucleosome remodelling activities, suggesting that EGL-27 is involved in chromatin remodelling. One further C.elegans gene,
egr-1 , is also similar to EGL-27 and MTA1. We found that
egl-27 and
egr-1 are functionally redundant, and have a fundamental role in embryonic patterning. When both are inactivated using RNAi, cells in essentially all regions of the embryo fail to be properly organised during gastrulation. However, tissue type determination appears normal and tissues become well-differentiated in these embryos. We assayed the expression of a number of embryonically expressed zygotic patterning genes (
vab-7 ,
lin-44 , and HOX genes) to see if their loss could explain the disorganised phenotype, but all are expressed normally. However,
hlh-8 , a target of the HOX gene
mab-5 , is not expressed, suggesting that
mab-5 requires
egl-27 to activate
hlh-8 . We propose that EGL-27 and EGR-1 function as part of a chromatin regulatory complex required for the function of regional transcription factor involved in embryonic patterning.