Meeting Abstract

P1.59  Tuesday, Jan. 4  Reduced cardiomyocyte proliferation and adhesion in embryos depleted for voltage-gated calcium channel beta subunit CACNB2. CHERNYAVSKAYA, Y*; EBERT, A; MILLIGAN, E; GARRITY, D; Colorado State University y.chernyavskaya@gmail.com

Voltage-gated calcium channels (VGCCs) are oligomeric complexes composed of pore-forming CACNA subunits and several auxiliary proteins. Auxiliary CACNB subunits regulate VGCC electrophysiology and chaperone CACNA subunits to the cell membrane. To determine the contributions of CACNB2 to cardiac development, we depleted zebrafish embryos of CACNB2 transcripts using morpholinos. CACNB2 morphant heart fields contained fewer cells expressing cardiac markers, suggesting fewer cardiomyocytes were specified, or diminished survival. Cell proliferation at later stages did not compensate for this deficiency; heart tubes in morphants contained 30% fewer cardiomyocytes at 48 hpf. We determined that cell proliferation was reduced in the morphants hearts via BrdU assay. Moreover, morphant heart tubes fragmented easily when placed under pressure, suggesting that cardiomyocyte adhesion was weakened. Consistent with this hypothesis, immunohistochemistry showed cadherins at cardiomyocyte membranes were depleted. Previous work showed that mutations in CACNA that inactivate cardiac VGCCs lead to atrial fibrillation. In contrast, heart rhythm was normal in CACNB2 morphants, suggesting that other CACNB proteins may compensate to provide intact VGCC activity. We are currently assaying whether CACNB2 phenotypes are mediated by loss of VGCC function per se, or by loss of other CACNB2:partner interactions. The latter possibility is intriguing in light of recent data suggesting that CACNBs, as MAGUK-family proteins, may interact with multiple protein partners via their SH3 or guanylate kinase domains.