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.