Transient expression of TIP60 protein during early chick heart development

Screening of an embryonic chick cDNA library revealed a gene product termed chick TIP60 (cTIP60) due to its homology with human TIP60, a founding member of the "MYST" family of proteins that possess functional motifs, including chromo, zinc finger, and histone acetyltransferase domains. cTIP60 expression was assessed during early chick embryogenesis, at the RNA level by using reverse transcriptase-polymerase chain reaction (RT-PCR) and at the protein level by using Western blotting and immunohistochemistry. RT-PCR indicated that cTIP60 transcripts in whole embryos are present as early as Hamburger-Hamilton (HH) stage 5, diminishing after HH10. Western blotting of total embryonic protein revealed that cTIP60 was present in uniform quantities between HH3 and HH25. By contrast, Western blotting of protein from isolated hearts revealed that cTIP60 protein was strongly expressed at the earliest stages of heart development (HH11-13), diminishing thereafter. This finding was corroborated by immunohistochemistry, which revealed that cTIP60 protein was selectively expressed at high levels in the myocardium between HH 10-14. Considered in the context of its functional domains, these findings suggest that cTIP60 modulates transcriptional processes which regulate terminal cell differentiation, proliferation, or both, during early myocardial development.