Cleft Palate Is Caused by CNS Dysfunction in Gad1 and Viaat Knockout Mice

Abstract

BackgroundPrevious studies have shown that disruption of GABA signaling in mice via mutations in the Gad1, Gabrb3 or Viaat genes leads to the development of non-neural developmental defects such as cleft palate. Studies of the Gabrb3 and Gad1 mutant mice have suggested that GABA function could be required either in the central nervous system or in the palate itself for normal palatogenesis.Methodology/Principal FindingsTo further examine the role of GABA signaling in palatogenesis we used three independent experimental approaches to test whether Gad1 or Viaat function is required in the fetal CNS for normal palate development. We used oral explant cultures to demonstrate that the Gad1 and Viaat mutant palates were able to undergo palatogenesis in culture, suggesting that there is no defect in the palate tissue itself in these mice. In a second series of experiments we found that the GABAA receptor agonist muscimol could rescue the cleft palate phenotype in Gad1 and Viaat mutant embryos. This suggested that normal multimeric GABAA receptors in the CNS were necessary for normal palatogenesis. In addition, we showed that CNS-specific inactivation of Gad1 was sufficient to disrupt palate development.Conclusions/SignificanceOur results are consistent with a role for Gad1 and Viaat in the central nervous system for normal development of the palate. We suggest that the alterations in GABA signaling lead to non-neural defects such as cleft palate as a secondary effect due to alterations in or elimination of fetal movements.

GAD65/GAD67 double knockout mice exhibit intermediate severity in both cleft palate and omphalocele compared with GAD67 knockout and VGAT knockout mice

“…GAD67 is the major GAD isoform at embryonic stages and its KO caused a drastic reduction of GABA content in neonatal mouse brains (Asada et al, 1997). The GAD67 KO, GABA-A receptor b3 subunit KO and VGAT KO mice displayed cleft palates (Asada et al, 1997;Condie et al, 1997;Homanics et al, 1997;Wojcik et al, 2006;Oh et al, 2010;Saito et al, 2010). These results suggest that GABAergic signaling plays a role in palate formation.…”

“…These results suggest that GABAergic signaling plays a role in palate formation. Furthermore, the VGAT KO and GAD67 KO mice also displayed omphalocele (Wojcik et al, 2006;Oh et al, 2010;Saito et al, 2010). Therefore, GABAergic signaling also seems to be involved in abdominal wall formation.…”

SDF and GABA interact to regulate axophilic migration of GnRH neurons

“…To directly observe GnRH neuronal movement during a dramatic reduction of endogenous GABA, cells were monitored in explants generated from two different lines of mice with altered GABA synthesis -GAD67 knockout (KO) and VIAAT KO (Oh et al, 2010). GAD67KO animals show a 90% reduction of GABA in the developing brain (Asada et al, 1997) and differences in the distribution of migrating GnRH neurons prenatally .…”

“…In addition, manipulation of myosin II, an indirect target of RhoA signaling, can lead to undirected movement of the nucleus orthogonal to the leading process in cortical interneurons (Bellion et al, 2005). Notably, CXCR4 receptors are rapidly internalized after activation (Peled et al, 2012) while GABA A receptors can directly bind to cell adhesion molecules (Zhang et al, 2010) and cytoskeletal adaptor proteins (Wang and Olsen, 2000). If adhesion were strongly enhanced after application of muscimol, a reduction in both total and linear movement might occur.…”

“…Embryos were removed and used for generating nasal explants or in vivo analysis. The Gad1/Gad67 knockout mice and Viaat KO mice have been described previously (Oh et al, 2010).…”