Identification and genomic cloning of CMHC1 - A unique myosin heavy chain expressed exclusively in the developing chicken heart

We report the identification and cloning of a unique chick myosin heavy cha in (CMHC1) that is expressed exclusively in the heart during embryogenesis. Using primers specific to myosin heavy chains, we used reverse transcripta se-polymerase chain reaction to clone and isolate CMHC1 from embryonic day 10 chicken heart RNA. Sequence analysis indicated that CMHC1 was a novel me mber of the myosin heavy chain family. Expression of the CMHC1 transcripts was detected in Hamburger Hamilton stage 10 chick embryos in the fusing myo cardium, Expression of CMHC1 was maintained at high levels throughout the t ubular heart of later stage embryos. Reverse transcriptase-polymerase chain reaction and in situ hybridizations failed to detect CMHC1 transcripts in the developing somites, limb buds, or skeletal musculature at any stage of chick development. Genomic CMHC1 clones have been isolated that contain seq uences approximately 5.2 kilobase upstream of the presumptive CMHC1 transcr iption start site. Portions of the upstream regulatory region induced a al- fold increase in reporter gene expression in primary cardiomyocytes, Becaus e of its unique cardiac-restricted expression, CMHC1 will provide an excell ent model system to study the molecular mechanisms required for the early d evelopmental regulation of heart-specific genes.