Connexins in the early development of the African clawed frog Xenopus laevis (Amphibia): The role of the connexin43 carboxyl terminal tail in the establishment of the dorso-ventral axis

Abstract

Connexins are a family of related proteins identified in vertebrate forming gap junctions, which mediate cell-to-cell communication in early embryos, with an important role in establishing embryonic asymmetry and 'communication compartments'. By in situ hybridization, immunocytochemistry, reverse transcriptase PCR (RT-PCR) and western blotting we show that a Cx43-like molecule is present in oocytes and embryos of the African clawed frog Xenopus laevis, with specific localization in the animal-vegetal axis. This specific distribution is suggestive for an important role for this protein in the establishment of the dorso-ventral axis. Antisense RNA and antibodies directed against rat carboxyl terminal tail of the Cx43 (CT-Cx43) and injected in 1-cell stage Xenopus embryos, induced pronounced alterations in nervous system development, with a severe ventralization phenotype. Coherently, the overexpression of CT-Cx43 produced a dorsalization of the embryos. In antisense treated embryos, the expression of the β-catenin gene is eliminated from the Nieuwkoop center, the pattern expression of the Chordin, Xnot and Xbra is modified, with no effect in expression of the Goosecoid gene. In CT-Cx43 mRNA treated embryos the pattern of expression of the β-catenin, Chordin, Goosecoid, Xnot and engrailed-2 genes is modified. The expression of β-catenin is increased in the Nieuwkoop center, the expression pattern of Chordin and Goosecoid is expanded to the posterior neural plate and engrailed-2 presents ectopic expression in the ventral region. Taken together our data suggest a role for CT-Cx43 as a maternal determinant with a critical function in the formation of the dorso-ventral axis in Xenopus laevis. The Cx43 may be one of the earliest markers of the dorso-ventral axis in these embryos and could possibly be acting through regionalization of factors responsible for the establishment of this axis.

Impaired Cx43 gap junction endocytosis causes morphological and functional defects in zebrafish

“…Another interesting revelation of this study is that impaired gap junction turnover exhibited in the cx43 lh10 embryos allows development into adulthood although, generally, with severe developmental defects, which is seemingly different from humans based on the ExAC database analysis described above. In the zebrafish embryo, Cx43 is expressed as early as 1.25hrs post-fertilization (8-cell stage) (Hardy et al, 1996;Chatterjee et al, 2005;Cofre et al, 2007), but cardiovascular morphological abnormalities in the cx43 lh10 embryos are only apparent beginning at ~24hrs post-fertilization. Also, the severity of phenotypes was observed to be quite variable in the cx43 lh10 mutant fish.…”

Kaiso and Prognosis of Cancer in the Current Epigenetic Paradigm

“…In this model direct connexin 43 changes the expression of p27/Kip1 (the cyclin-dependent kinase inhibitor). Importantly, Cx43, or at least the carboxy terminal tail of this protein has been localized within the nucleus with the use of immunohistochemistry, confirming an intracellular regulatory role (Dang et al, 2003;Cofre & Abdelhay, 2007).…”

Altering metabolite distribution at Xenopus cleavage stages affects left–right gene expression asymmetries

“…It also will be important to test whether increasing the endogenous metabolites affect cell fate and/or gene expression. Injected metabolites, by virtue of their charge, could alter the normal flow of molecules through gap junctional complexes that are known to be active during cleavage stages (Adams et al, 2006;Cofre & Abdekhay, 2007;Warner, Guthrie, & Gilula, 1984). It is plausible that changes in metabolite distribution alter cytoskeletal organization, which could affect cell movements and/or cell division rates or orientation.…”