Role of Specc1l in ciliogenesis during craniofacial development

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Project Summary Craniofacial anomalies constitute a third of all congenital malformations. Orofacial clefts (OFCs) are among the most common congenital malformations, affecting approximately 1 in 700 births. OFCs are complex diseases caused by multiple genetic and environmental factors. Incomplete understanding of the mechanisms underlying OFCs suggests a continued need to identify genes that contribute to its pathogenesis. Mutations in SPECC1L have been identified in patients with syndromic and nonsyndromic cleft lip and/or palate. Syndromic SPECC1L mutations cluster in the second coiled coil domain (CCD2), which facilitates interaction of this cytoskeletal protein with microtubules. Our recent studies indicate that mice with an in-frame deletion of SPECC1L-CCD2 exhibit cleft palate and exencephaly in a dominant-negative manner. Notably, OFC and exencephaly are common manifestations of ciliopathies – human disorders which arise from disruption of primary cilia – but an association between SPECC1L and primary cilia has not been reported. In addition to association with actin filaments and microtubules in the cytoskeleton, SPECC1L localizes to the pericentriolar region at the cilia base, but this localization is diminished in Specc1l∆CCD2/∆CCD2 palatal mesenchyme. In addition, primary cilia lengths are decreased in Specc1l∆CCD2/∆CCD2 palatal mesenchyme and epithelium relative to wild-type, on both the lingual and buccal sides of the palate. In Specific Aim 1, I will investigate the hypothesis that an intracellular trafficking defect in the palatal mesenchyme results in shortened cilia and that the shortened cilia affect signaling in the palatal mesenchyme. Since the IFT-A mouse mutant, Thm1aln/aln, shares overlapping phenotypes with Specc1l mutant mice, including cleft palate, exencephaly, and shortened cilia, we hypothesize that Specc1l and Thm1 genetically interact. In Specific Aim 2, I will investigate the interaction between Specc1l and Thm1, which we propose converges on ciliogenesis. Previous studies have shown that conditional loss of Thm1 in neural crest cells (NCCs), which give rise to the palatal mesenchyme, results in cleft palate, and that Specc1l deficiency leads to NCC delamination defect. Our preliminary data shows that cilia lengths of NCCs are decreased upon Specc1l deficiency. Thus, we propose that the genetic interaction between Specc1l and Thm1 is mediated via NCC function. Overall, this proposal will reveal a novel role for SPECC1L in ciliogenesis in multiple aspects of craniofacial development.