Expression of intermediate filament proteins during development of Xenopus laevis: I.cDNA clones encoding different forms of vimentin

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Abstract
To provide a basis for studies of the expression of genes encoding the diverse kinds of intermediate-filament (IF) proteins during embryogenesis of Xenopus laevis we have isolated and characterized IF protein cDNA clones. Here we report the identification of two types of Xenopus vimentin, Viml and Vim4, with their complete amino acid sequences as deduced from the cloned cDNAs, both of which are expressed during early embryogenesis. In addition, we have obtained two further vimentin cDNAs (Vim2 and 3) which are sequence variants of closely related Viml. The high evolutionary conservation of the amino acid sequences (Viml: 458 residues; Mr ∼ 52800; Vim4: 463 residues; Mr∼ 53500) to avian and mam malian vimentin and, to a lesser degree, to desmin from the same and higher vertebrate species, is emphasized, including conserved oligopeptide motifs in their head domains. Using these cDNAs in RNA blot and ribonu clease protection assays of various embryonic stages, we observed a dramatic increase of vimentin RNA at stage 14, in agreement with immunocytochemical results ob tained with antibody VIM-3B4. The significance of very weak mRNA signals detected in earlier stages is dis cussed in relation to negative immunocytochemical re sults obtained in these stages. The first appearance of vimentin has been localized to a distinct mesenchymal cell layer underlying the neural plate or tube, respect ively. The results are discussed in relation to programs of de novo synthesis of other cytoskeletal proteins in amphibian and mammalian development.