Molecular characterization of a novel atrial-specific myosin heavy-chain gene expressed in the chick embryo

A 1.2 kb fragment of a myosin heavy-chain (MHC) gene was isolated from the complementary DNA (cDNA) library derived from embryonic day 15 (E15), Hamburger and Hamilton (H.H) stage 41 chick embryonic ventricle, using a fragment of human beta-cardiac MHC cDNA as a probe. DNA sequence analysis determined that the gene (CCSV2) encoded the amino acid sequence of the rod portion (part of S2 and light meromyosin) of the chick atrial-specific MHC gene. The nucleotide sequence of CCSV2 was slightly different (90% homologous) from a previously reported atrial-specific MHC (AMHC1) expressed in chick embryo. Northern blot analysis, with the CCSV2 fragment (1.2 kb) used as a probe, showed that the gene is expressed intensively in the developing chick atrial muscle, but weakly in the ventricle and pectoralis muscle. S1-nuclease mapping analysis, with CCSV2 used as a probe, demonstrated a fully protected fragment in the atrium and ventricle. In this study, no intensive signal of a partially protected fragment was detected in the atrium. On the other hand, not only a fully protected fragment, but also four partially protected fragments were observed in the pectoralis muscle. Whole-mount in situ hybridization was performed in developing chick heart at H.H. stages 19, 21 and 30. The hybridization signal was intensive in the primitive atrium (H.H. stages 19 and 21) and in the atrial appendages derived from the primitive atrium (H.H. stage 30). Weak signals were detected in the primitive ventricle (H.H. stages 19 and 21), the ventricle (H.H. stage 30) and in the somites (H.H. stages 19 and 21).(ABSTRACT TRUNCATED AT 250 WORDS)