Neural crest cell-specific deletion of Rac1 results in defective cell–matrix interactions and severe craniofacial and cardiovascular malformations

Abstract

The small GTP-binding protein Rac1, a member of the Rho family of small GTPases, has been implicated in regulation of many cellular processes including adhesion, migration and cytokinesis. These functions have largely been attributed to its ability to reorganize cytoskeleton. While the function of Rac1 is relatively well known in vitro, its role in vivo has been poorly understood. It has previously been shown that in neural crest cells (NCCs) Rac1 is required in a stage-specific manner to acquire responsiveness to mitogenic EGF signals. Here we demonstrate that mouse embryos lacking Rac1 in neural crest cells (Rac1/Wnt1-Cre) showed abnormal craniofacial development including regional ectodermal detachment associated with mesenchymal acellularity culminating in cleft face at E12. Rac1/Wnt1-Cre mutants also displayed inappropriate remodelling of pharyngeal arch arteries and defective outflow tract septation resulting in the formation of a common arterial trunk (‘persistent truncus arteriosus’ or PTA). The mesenchyme around the aortic sac also developed acellular regions, and the distal aortic sac became grossly dysmorphic, forming a pair of bilateral, highly dilated arterial structures connecting to the dorsal aortas. Smooth muscle cells lacking Rac1 failed to differentiate appropriately, and subpopulations of post-migratory NCCs demonstrated aberrant cell death and attenuated proliferation. These novel data demonstrate that while Rac1 is not required for normal NCC migration in vivo, it plays a critical cell-autonomous role in post-migratory NCCs during craniofacial and cardiac development by regulating the integrity of the craniofacial and pharyngeal mesenchyme.

Wnt9b-dependent FGF signaling is crucial for outgrowth of the nasal and maxillary processes during upper jaw and lip development

“…Consistent with this notion, ectoderm-and mesenchyme-specific deletion of Rac1, Cdc42 or RhoA in the facial processes does not result in any notable phenotypic defects in facial structures until E10.5 (Chen et al, 2006;Fuchs et al, 2009;Thomas et al, 2010;Katayama et al, 2011). No morphological hypoplasia was found in the NP and MxP of mesenchyme-specific Rac1 and Cdc42 mutant mice at E11 (Fuchs et al, 2009;Thomas et al, 2010).…”

“…No morphological hypoplasia was found in the NP and MxP of mesenchyme-specific Rac1 and Cdc42 mutant mice at E11 (Fuchs et al, 2009;Thomas et al, 2010). Severe malformations of neural crest-derived structures and mid-facial cleft appeared in these mutants at ~E11.5.…”

A Stable Cranial Neural Crest Cell Line from Mouse

“…Postmigratory neural crest cells express their own unique set of markers, including Barx1, Prrx1 (Prx1), and Rarg [43][44][45]. Rac1 functions in both the migratory and postmigratory neural crest [46][47][48]. Our array analysis revealed that O9-1 cells express genes typical of each category, including the migratory neural crest markers and the postmigratory markers.…”

Cell organization, growth, and neural and cardiac development require αII-spectrin

“…Spectrin participates in the activation of the Rho GTPase Rac, and overexpression of the aII-spectrin SH3 domain inhibits Rac1 activation, actin filament formation, and cell spreading in cultured cells (Bialkowska et al, 2005). Interestingly, actin and Rac1 have also been implicated in the regulation of neuronal polarity and axon formation via the WAVE complex (Tahirovic et al, 2010), and the loss of Rac1 in neural crest cells leads to severe craniofacial and cardiovascular malformations (Thomas et al, 2010). We thus anticipate that a major effector pathway disrupted in the Spna2 2/2 animals will be Rac-mediated actin regulation.…”