RESUMO
The C. elegans MS blastomere, born at the 7-cell stage of embryogenesis, generates primarily mesodermal cell types, including pharynx cells, body muscles and coelomocytes. A presumptive null mutation in the T-box factor gene tbx-35, a target of the MED-1 and MED-2 divergent GATA factors, was previously found to result in a profound decrease in the production of MS-derived tissues, although the tbx-35(-) embryonic arrest phenotype was variable. We report here that the NK-2 class homeobox gene ceh-51 is a direct target of TBX-35 and at least one other factor, and that CEH-51 and TBX-35 share functions. Embryos homozygous for a ceh-51 null mutation arrest as larvae with pharynx and muscle defects, although these tissues appear to be specified correctly. Loss of tbx-35 and ceh-51 together results in a synergistic phenotype resembling loss of med-1 and med-2. Overexpression of ceh-51 causes embryonic arrest and generation of ectopic body muscle and coelomocytes. Our data show that TBX-35 and CEH-51 have overlapping function in MS lineage development. As T-box regulators and NK-2 homeodomain factors are both important for heart development in Drosophila and vertebrates, our results suggest that these regulators function in a similar manner in C. elegans to specify a major precursor of mesoderm.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/anatomia & histologia , Caenorhabditis elegans/embriologia , Proteínas de Homeodomínio/metabolismo , Mesoderma/fisiologia , Proteínas com Domínio T/metabolismo , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Animais , Animais Geneticamente Modificados , Blastômeros/fisiologia , Caenorhabditis elegans/crescimento & desenvolvimento , Proteínas de Caenorhabditis elegans/genética , Linhagem da Célula , Regulação da Expressão Gênica no Desenvolvimento , Técnicas de Inativação de Genes , Redes Reguladoras de Genes/fisiologia , Proteínas de Homeodomínio/genética , Dados de Sequência Molecular , Fenótipo , Interferência de RNA , Proteínas Recombinantes de Fusão/genética , Proteínas Recombinantes de Fusão/metabolismo , Alinhamento de Sequência , Proteínas com Domínio T/genética , Fatores de Transcrição/genéticaRESUMO
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.
Assuntos
Proteínas de Caenorhabditis elegans/metabolismo , Caenorhabditis elegans/embriologia , Caenorhabditis/embriologia , Proteínas de Ligação a DNA/metabolismo , Endoderma/embriologia , Proteínas de Grupo de Alta Mobilidade/metabolismo , Mesoderma/embriologia , Fatores de Transcrição/metabolismo , Sequência de Aminoácidos , Animais , Animais Geneticamente Modificados , Padronização Corporal , Caenorhabditis/genética , Caenorhabditis elegans/metabolismo , Embrião não Mamífero/anormalidades , Embrião não Mamífero/metabolismo , Endoderma/anormalidades , Regulação da Expressão Gênica no Desenvolvimento , Mesoderma/metabolismo , Modelos Biológicos , Dados de Sequência Molecular , Faringe/anormalidades , Fenótipo , Interferência de RNA , Homologia de Sequência de Aminoácidos , Proteínas Wnt/metabolismoRESUMO
In C. elegans, many mesodermal cell types are made by descendants of the progenitor MS, born at the seven-cell stage of embryonic development. Descendants of MS contribute to body wall muscle and to the posterior half of the pharynx. We have previously shown that MS is specified by the activity of the divergent MED-1,2 GATA factors. We report that the MED-1,2 target gene tbx-35, which encodes a T-box transcription factor, specifies the MS fate. Embryos homozygous for a putative tbx-35-null mutation fail to generate MS-derived pharynx and body muscle, and instead generate ectopic PAL-1-dependent muscle and hypodermis, tissues normally made by the C blastomere. Conversely, overexpression of tbx-35 results in the generation of ectopic pharynx and muscle tissue. The MS and E sister cells are made different by transduction of a Wnt/MAPK/Src pathway signal through the nuclear effector TCF/POP-1. We show that in E, tbx-35 is repressed in a Wnt-dependent manner that does not require activity of TCF/POP-1, suggesting that an additional nuclear Wnt effector functions in E to repress MS development. Genes of the T-box family are known to function in protostomes and deuterostomes in the specification of mesodermal fates. Our results show that this role has been evolutionarily conserved in the early C. elegans embryo, and that a progenitor of multiple tissue types can be specified by a surprisingly simple gene cascade.
