Click here to close
Hello! We notice that you are using Internet Explorer, which is not supported by Xenbase and may cause the site to display incorrectly.
We suggest using a current version of Chrome,
FireFox, or Safari.
???displayArticle.abstract???
In birds and mammals three isoforms of troponin I (TnI) exist; a slow (TnIs), a fast (TnIf) and a cardiac (TnIc). Although each of these isoforms is expressed in the adult forms of these organisms in a muscle fiber-type-specific manner, the gene encoding TnIs is also expressed within the developing heart of these vertebrates. Herein, our results demonstrate that the developing heart of Xenopus laevis, unlike its counterpart in birds and mammals, does not express the gene encoding the TnIs isoform and that the expression of this gene, as well as the one encoding the Xenopus TnIf isoform, is restricted to skeletal muscle.
???displayArticle.pubmedLink???
12049779
???displayArticle.link???Mech Dev
Fig. 2. Expression of Xenopus troponin I isoforms during various stages of development. (A) Whole-mount in situ hybridizations using antisense riboprobes for the troponin I fast (A–D), slow (E–H) and cardiac (I,J) mRNA isoforms during Xenopus embryogenesis (A–D and E–H represent Xenopus developmental stages 15, 22, 30 and 36 (Nieuwkoop and Faber, 1967)). Black arrows indicate the location of the hypaxial muscles while white arrows denote the location of XTnIc expression in the heart of Stage 28 (I) and Stage 30 (J) embryos. (B) RT–PCR analysis of the TnI isoforms in RNA isolated from the (A) tadpoleheart, (B) tadpoletail, (C) frog heart and (D) frog limb muscles. Primer pairs specific for XTnIf (f), XTnIs (s) and XTnIc (c) were used to amplify DNA fragments of the expected sizes (f=363 bp; s=505 bp; c=874 bp). Lane M shows standard DNA size markers (1 Kb Plus DNA Ladder; Invitrogen Life Technologies).
tnni2 (troponin I type 2 (skeletal, fast), gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 15, dorsal view, anteriorleft.
tnni2 (troponin I type 2 (skeletal, fast), gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 22, lateral view, anteriorleft, dorsal up.
tnni1.2 (troponin I type 1 (skeletal, slow), gene 2 ) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 15, dorsal view, anteriorleft.
tnni1.2 (troponin I type 1 (skeletal, slow), gene 2 ) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 22, lateral view, anteriorleft, dorsal up.
Fig. 1.
Sequence comparisons of Xenopus troponin I isoforms. (A) Alignment of the derived amino acid sequences of Xenopus troponin I cardiac (XTnIc; Drysdale et al., 1994), slow (XTnIs) and fast (XTnIf) isoforms. Comparisons were performed using Clustal X (Thompson et al., 1997). Dark shading denotes identical amino acids, light shading designates similar amino acids and dots indicate the location of insertions/deletions. (B) A phylogenetic tree based on the amino acid sequences of the troponin I fast, slow and cardiac isoforms from Xenopus, quail (M12132; U37118; M73702), mouse (J04992; NM_021467; U09181) and human (L21715; J04760; M64247). The neighbor-joining tree was prepared using TREECON ( Van de Peer and De Wachter, 1994) with the bootstrap values (based on 1000 iterations) shown at each node.
