Reevaluation of the role of the med-1 and med-2 genes in specifying the Caenorhabditis elegans endoderm.
The med-1 and med-2 genes encode a pair of essentially identical GATA factor-related transcription factors that have been proposed to be necessary for specification of the C. elegans endoderm (intestine or E lineage) as well as part of the C. elegans mesoderm. med-1 and med-2 are proposed to be the direct downstream targets and the principal effectors of the maternally provided SKN-1 transcription factor; med-1 and med-2 would thus occupy the pivotal interface between maternal and zygotic control of gene expression. The conclusion that med-1 and med-2 are necessary for C. elegans endoderm specification was based on a partially penetrant (approximately 50%) loss of endoderm markers produced by RNA-mediated interference (RNAi). To determine whether this partial penetrance reflects: (i) inefficient RNAi against early zygotic transcripts, (ii) experimental uncertainty in the expected level of endoderm loss in skn-1 nulls, or (iii) additional redundancy in the pathway of endoderm specification, we constructed worm strains that segregate embryos lacking both the med-1 gene (because of a gene-specific deletion) and the med-2 gene (using either of two chromosomal deficiencies). Contrary to expectations, we observe that only approximately 3-20% of med-2(-); med-1(-) embryos do not express markers of endoderm differentiation. Furthermore, we found no evidence for a maternal contribution of the med genes to endoderm specification. We conclude that the major pathway(s) for endoderm specification in C. elegans must be independent of the med-1 and med-2 genes.
Department of Biochemistry and Molecular Biology, Genes and Development Research Group, University of Calgary, Alberta, Canada.
Barbara
B
Goszczynski
James D
JD
McGhee
D000818:Animals; D017173:Caenorhabditis elegans / Q000196:embryology* / Q000235:genetics; D029742:Caenorhabditis elegans Proteins / Q000235:genetics* / Q000378:metabolism; D002454:Cell Differentiation / Q000235:genetics* / Q000502:physiology; D019070:Cell Lineage / Q000235:genetics* / Q000502:physiology; D017931:DNA Primers; D004268:DNA-Binding Proteins / Q000378:metabolism; D004707:Endoderm / Q000502:physiology*; D050980:GATA Transcription Factors / Q000235:genetics* / Q000378:metabolism; D017353:Gene Deletion; D018507:Gene Expression Regulation, Developmental / Q000235:genetics*; D005819:Genetic Markers / Q000235:genetics; D034622:RNA Interference; D014157:Transcription Factors / Q000378:metabolism
D029742:Caenorhabditis elegans Proteins; D017931:DNA Primers; D004268:DNA-Binding Proteins; D050980:GATA Transcription Factors; D005819:Genetic Markers; C433251:MED-1 protein, C elegans; C433252:MED-2 protein, C elegans; D014157:Transcription Factors; C073702:skn-1 protein, C elegans