The Drosophila SPECC1L homolog, Split Discs, co-localizes with non-muscle myosin II and regulates focal adhesion dynamics

ABSTRACT Allelic variations of Sperm antigen with calponin homology and Coiled-Coil domains 1 Like (SPECC1L) have been associated with a spectrum of cranial-facial pathologies including Teebi hypertelorism and Opitz G/BBB syndrome which manifest as clefting of the palate, wide-eyes, and incomplete closure of the esophagus among others. These pathologies may be indicative of improper cranial neural crest cell (CNCC) delamination and migration. SPECC1L is hypothesized to be an actin-microtubule cross-linking protein as it co-localizes with both microtubules and actin in tissue culture cells. Further, it has been shown to immunoprecipitate with a protein phosphatase complex-1β (PP1β) member, MYPT1, as well as being involved in the PI3K-AKT signaling axis. In this study we sought to investigate the SPECC1L Drosophila homolog Spdi and despite sharing close homology with its mammalian counterpart we found that Spdi is associated with both non-muscle myosin-II and actin. RNAi depletion of Spdi led to an increase in focal adhesion dynamics and when we introduced conserved point mutations to Spdi that are analogous to those associated with human disease we observed a further increase in focal adhesion dynamics above that of depletion alone. Collectively, our findings suggest that Spdi is a non-muscle myosin II (NMII) binding protein that likely affects focal adhesion dynamics through this association. Our results also suggest that some of the pathologies associated with allelic variants of SPECC1L may be the result of aberrant cell-matrix adhesion. Competing Interest Statement The authors have declared no competing interest. - Spdi - Split Discs - CNCC - cranial neural crest cell - PP1 - phosphatase complex-1 - SPECC1L - Sperm antigen with calponin homology and Coiled-Coil domains 1 Like - CIL - contact inhibition of locomotion - CH - calponin homology - CC - Coiled-coil - Sqh - Spaghetti Squash (NMII regulatory light chain) - Zip - Zipper (NMII heavy chain) - Mhc1 - myosin heavy chain-like - RLC - regulatory light chain - ELC - essential light chain - UTR - untranslated region