Alternative splicing, phylogenetic analysis, and craniofacial expression of zebrafishtbx22

Abstract

Mutations in human TBX22 cause X-linked cleft palate with ankyloglossia syndrome (CPX; OMIM 303400). Since the secondary palate was an adaptation to breathing on land, we characterized zebrafish tbx22 to study molecular mechanisms regulating early vertebrate craniofacial patterning. Rapid Amplification of cDNA Ends (RACE) analyses revealed two zebrafish tbx22 splice isoforms, tbx22-1 and tbx22-2, encoding proteins of 444 and 400 amino acids, respectively. tbx22-1 resembles canonical Tbx22 orthologs, while tbx22-2 lacks conserved N-terminal sequence. Developmental RT-PCR revealed that tbx22-1 is maternally and zygotically expressed, while tbx22-2 is expressed zygotically. WISH analyses revealed strong tbx22 mRNA expression in ectomesenchyme underlying the stomodeum, a bilaminar epithelial structure demarcating early mouth formation, and in early presumptive jaw joints. Zebrafish tbx22 expression mirrored some aspects of mammalian Tbx22, consistent with roles in early vertebrate face patterning. These studies identify an early transcription factor governing vertebrate facial development, which may underlie common craniofacial birth disorders.

The function and regulation of TBX22 in avian frontonasal morphogenesis

“…Thus, de novo expression occurred sometime after the cessation of neural crest cell migration. A similar result has recently been reported in zebrafish, where expression around the mouth is not detected until relatively late in organogenesis (Jezewski et al, 2009). TBX22 is a mesenchymally restricted transcription factor and the upregulation in the facial mesenchyme is presumably dependent on local interactions with epithelium or perhaps with the forebrain in the case of the frontonasal mass (Marcucio et al, 2005;Hu and Marcucio, 2009).…”

“…In situ hybridization studies in amniotes have documented expression of TBX22 in the frontonasal mass and maxillary prominences of chickens (Haenig et al, 2002;Handrigan et al, 2007), mice (Braybrook et al, 2002;Bush et al, 2002;Herr et al, 2003), and humans (Braybrook et al, 2002). The high degree of evolutionary conservation was recently confirmed in zebrafish, where expression is also restricted to the perioral mesenchyme (Jezewski et al, 2009). Interestingly, despite the expression of TBX22 in the frontonasal mass, mutations in the human gene primarily affect fusion of the maxillary-derived secondary palate (CPX, OMIM 303400; Braybrook et al, 2001;Marcano et al, 2004;Stanier and Moore, 2004;Suphapeetiporn et al, 2007).…”

Regulation of Tbx22 during facial and palatal development

“…Consistent with the observed defects in CPX patients, expression analysis in all three species and in human embryos revealed expression in the frontonasal region and the first branchial arch, and subsequently in the developing palate and base of the tongue (Braybrook et al, 2002;Bush et al, 2002;Haenig et al, 2002;Herr et al, 2003;Welsh et al, 2007;Jezewski et al, 2009). Gene-targeting experiments in the mouse confirmed a conserved function of mouse Tbx22 in palatogenesis (Pauws et al, 2009a).…”

Early expression of the <i>tbx</i>22 gene in zebrafish influences positioning of pharyngeal arch cartilages

“…Characterization of several tbx genes suggests a role for these genes in craniofacial development [12][13][14]. tbx22 is a member of the tbx1 subfamily, which consists of tbx1, 10, 15, 18, 20, 22 [9].…”

“…tbx1 has been shown to regulate oral epithelial adhesion and palatal development [15] and the van gogh/tbx1 zebrafish mutant results in severe craniofacial defects similar to the complex defects found in DiGeorge syndrome [16]. Mutations in the human tbx22 gene cause syndromic, X-linked cleft pa-late/ankyloglossia and also strongly contribute to nonsyndromic cleft lip and/or cleft palate and cleft palate alone [13,[17][18][19][20][21]. Therefore, we asked whether or not zebrafish tbx22 plays a similar role in palate formation and what role it plays in craniofacial development.…”