Overexpression of connexin43 alters the mutant phenotype of midgestational wnt‐1 null mice resulting in recovery of the midbrain and cerebellum

Abstract

The midbrain-hindbrain (MHB) junction plays a key role in the patterning of the embryonic neural tube and the formation of brain structures such as the cerebellum. The mitogen wnt-1 is critical for cerebellar development, as evidenced by the lack of MHB region and cerebellar formation in the wnt-1 null embryo. We have generated wnt-1 null embryos overexpressing the gap junction gene connexin43 by crossing wnt-1 null heterozygotes into the CMV43 mouse line. We have confirmed that these mice show an increase in gap junctional communication by dye coupling analysis. Two-thirds of wnt-1 null CMV43ϩ mouse embryos at E18.5 have a cerebellum. In addition, changes in the wnt-1 null phenotype in mouse embryos overexpressing connexin43 are observed as early as E9.5. At this stage, one-quarter of wnt-1 null CMV43 ϩ embryos display extra or expanded tissue present at the MHB boundary (a wnt-1 null enlarged phenotype). In situ hybridization studies conducted on these embryos have indicated no changes in the expression of embryonic brain positional markers in this region. We conclude from these studies that overexpression of the connexin43 gap junction restores cerebellar formation by compensating for the loss of wnt-1.

Precerebellar Cell Groups in the Hindbrain of the Mouse Defined by Retrograde Tracing and Correlated with Cumulative Wnt1-Cre Genetic Labeling

“…The chick/quail grafting study of Marin and Puelles [56] suggested that the auricle of the chick cerebellum (equivalent to the flocculonodular node of mammals) arises from cells in r2 boundary, but in the absence of confirmatory data in mammals this suggestion must be considered speculative. The intense X-gal staining in the cerebellum is consistent with studies showing that Wnt1 is critical for cerebellar development [57].…”

Gap Junctions and Biophysical Regulation of Bone Cells

“…These effects were blocked by the nitric oxide (NO) inhibitor l -NG-nitroarginine methyl ester ( l -NAME), suggesting that NO may play a role in this mechanism. In addition, cerebellar formation defects found in Wnt-1 knockout mice are reversed by Cx43 overexpression [106]. These findings are consistent with earlier work, showing that Cx43 is a functional target of Wnt signaling in the brain [107].…”

The connexin43-dependent transcriptome during brain development: Importance of genetic background

“…In support of this hypothesis, we have found major sex dependent differences in gene expression changes in heart ventricles and atria (Iacobas et al, 2010), and it was reported that transgenic deletion of the astrocyte-specific gap junction gene Gja1 (encoding Cx43) in a GFAP-targeted strategy led to markedly different morphological and behavioral phenotypes in two different mouse strains (Wiencken-Barger et al, 2007). Moreover, these results were reminiscent of the profound destruction of the midbrain-hindbrain region obtained when the mitogen Wnt1 was deleted (Melloy et al, 2005); strikingly, when the authors crossed Wnt-1 heterozygotes into a Cx43 overexpressing mouse line, the expression of anatomically correct cerebellum was rescued in a substantial percentage of offspring (Melloy et al, 2005). Thus, the loss of one signaling molecule can be compensated by overexpression of a gap junction protein.…”