RESUMEN
Early work on the formation of the vertebrate body axis indicated the existence of separate head- and trunk-inducing regions in Spemann's organizer of the amphibian gastrula. In mammals some head-organizing activity may be located in anterior visceral (extraembryonic) endoderm (AVE). By analogy, the equivalent structure in the Xenopus laevis gastrula, the anterior endoderm, has been proposed to be the amphibian head organizer. Here we review recent data that challenge this notion and indicate that the involvement of AVE in head induction seems to be an exclusively mammalian characteristic. In X. laevis and chick, it is the prechordal endomesoderm that is the dominant source of head-inducing signals during early gastrulation. Furthermore, head induction in mammals needs a combination of signals from anterior primitive endoderm, prechordal plate, and anterior ectoderm. Thus, despite the homology of vertebrate anterior primitive endoderm, a role in head induction seems not to be conserved.
Asunto(s)
Endodermo/fisiología , Cabeza/embriología , Vertebrados/embriología , Animales , Humanos , Mamíferos/embriología , Xenopus laevis/embriologíaRESUMEN
The anterior endomesoderm of the early Xenopus gastrula is a part of Spemann's organizer and is important for head induction. Here we describe Xblimp1, which encodes a zinc finger transcriptional repressor expressed in the anterior endomesoderm. Xblimp1 represses trunk mesoderm and induces anterior endomesoderm in a cooperative manner with the pan-endodermal gene Mix.1. Furthermore, Xblimp1 can cooperate with the BMP inhibitor chordin to induce ectopic heads, while a dominant-negative Xblimp1 inhibits head formation. The head inducer cerberus is positively regulated by Xblimp1 and is able to rescue microcephalic embryos caused by dominant-negative Xblimp1. Our results indicate that Xblimp1 is required for anterior endomesodermal cell fate and head induction.
Asunto(s)
Péptidos y Proteínas de Señalización Intercelular , Mesodermo/metabolismo , Proteínas/genética , Proteínas Represoras/genética , Proteínas de Xenopus , Dedos de Zinc/genética , Secuencia de Aminoácidos , Animales , Proteínas Morfogenéticas Óseas/antagonistas & inhibidores , Clonación Molecular , Inducción Embrionaria/genética , Regulación del Desarrollo de la Expresión Génica , Glicoproteínas/metabolismo , Cabeza/embriología , Proteínas de Homeodominio/metabolismo , Hibridación in Situ , Microinyecciones , Datos de Secuencia Molecular , Proteínas/metabolismo , ARN Mensajero/metabolismo , Proteínas Represoras/química , Alineación de Secuencia , Xenopus/embriologíaRESUMEN
We have cloned a P-type ATPase gene from the aquatic fungus Blastocladiella emersonii (BePAT1) using a probe obtained with degenerate oligonucleotides, corresponding to two amino acid sequences highly conserved among all P-type ATPase isoforms, and the polymerase chain reaction technique. Nucleotide sequence analysis revealed a 3.4 kb open reading frame encoding a putative peptide of 1080 amino acid residues with a calculated molecular mass of 119 kDa, which presents all diagnostic features of P-type transporting ATPases. Comparison to other members of the family and phylogenetic analyses have shown that the BePAT1 protein belongs to the subfamily of Na,K- and H,K-ATPases, indicating that the divergence between the alpha-subunit of the Na,K-ATPase and other members of the P-type ATPase family has occurred before the divergence between the animal and fungal lineages in evolution.