RESUMO
In order to identify prospective limb muscle cells in a frog, we cloned Lbx1 from the direct developing frog Eleutherodactylus coqui. Like in embryos of the frog Xenopus laevis but unlike in other vertebrates, EcLbx1 is expressed in all trunk somites. Like in embryos of chick, mouse, and zebrafish, cells expressing EcLbx1 are then found in limb buds, consistent with migration of those cells from somites. EcLbx1 is also expressed in the dorsal spinal cord as in other vertebrates.
Assuntos
Anuros/embriologia , Extremidades/embriologia , Regulação da Expressão Gênica no Desenvolvimento/fisiologia , Proteínas de Homeodomínio/metabolismo , Somitos/metabolismo , Sequência de Aminoácidos , Animais , Anuros/anatomia & histologia , Clonagem Molecular , Primers do DNA/genética , Embrião não Mamífero/anatomia & histologia , Extremidades/anatomia & histologia , Havaí , Proteínas de Homeodomínio/genética , Hibridização In Situ , Dados de Sequência Molecular , Filogenia , Porto Rico , Medula Espinal/metabolismoRESUMO
The transcription factor, VegT, is the meso-endodermal determinant in Xenopus laevis. We examined VegT orthologs from several anuran amphibians and the urodele amphibian, the Mexican axolotl. In addition to the conserved T-box, the DNA-binding domain, the orthologs share a conserved 57 amino acid domain at the C-terminal. Most striking is a 17-nucleotide (nt) sequence near the 3' end of the open reading frame. The 17 nts are absolutely conserved among the anurans, whose last common ancestor lived 200 million years ago. As an initial test of the function of the 17 nts, 27 or 49 amino acids, which include the six amino acids coded by the 17 (+1) nts, were deleted from the C-terminal of VegT. These truncated VegT's retained some transcriptional activity, indicating that the 17 nts are not absolutely required for this function. The function of the highly conserved 17 nts is unknown. Two possibilities are that the conserved 17 nts interact with the cytoskeleton or that they are a target for regulation by a microRNA.
Assuntos
Proteínas de Anfíbios/metabolismo , Sequência Conservada/fisiologia , Endoderma/metabolismo , Regulação da Expressão Gênica no Desenvolvimento , Mesoderma/metabolismo , Proteínas com Domínio T/fisiologia , Proteínas de Xenopus/fisiologia , Sequência de Aminoácidos , Proteínas de Anfíbios/classificação , Animais , Clonagem Molecular , Feminino , Dados de Sequência Molecular , Alinhamento de Sequência , Proteínas com Domínio T/genética , Xenopus/crescimento & desenvolvimento , Proteínas de Xenopus/genéticaRESUMO
Specification of the dorsal axis in commonly studied frogs, such as Xenopus laevis and Rana pipiens, depends on a microtubule-mediated movement of cytoplasm in the fertilized egg. The Puerto Rican tree frog, Eleutherodactylus coqui, has an egg that is twenty times the volume of that of X. laevis, raising the question as to whether the mechanism of dorsal axial specification is conserved in these large eggs. Fertilized eggs of E. coqui develop a transient array of parallel microtubules, similar to other frogs, but proportionately larger. The array persists after first cleavage, longer than in other frogs, and is gone by the third cleavage. Correlated with the longer life of the parallel microtubules, both 2- and 8-cell E. coqui embryos remain sensitive to gravity-mediated axial specification, a sensitivity lost in X. laevis before the 2-cell stage. Activation of the Wnt/beta-catenin pathway by injected Xwnt8 RNA causes axial formation as in X. laevis. The results indicate that elements of dorsal axial specification are conserved in E. coqui, but they occur later compared to in X. laevis.