The developmentally regulated expression of two linked myosin heavy-chain genes

The organization of two linked chicken myosin heavy-chain (MHC) genes is described. Using probes derived from the 3' and 5' ends of the genes, chromosome walks were carried out, resulting in the isolation of a clone which encompassed the 5' end of one MHC gene and the 3' end of a different MHC gene. Further analysis showed that both genes (each approximately 25 kbp in length) are oriented head to tail and are separated by an intergenic region of 7.5 kbp. Despite extensive homologies, a transcript-specific probe for each of the genes could be prepared from the 5' untranslated regions. These probes were used to determine the transcriptional pattern for each of the genes. The data show that the gene located at the 5' end of the linkage pair is expressed during the neonatal stages of development, while the gene located at the 3' end of the pair is expressed predominantly during the embryonic stages of development.