Novel cell lines promote the discovery of genes involved in early heart development

Clonal cell lines representing early cardiomyocytes would provide valuable reagents for the dissection of the genetic program of early cardiogenesis. Here we describe the establishment and characterization of cell lines from the hearts of transgenic mice and embryos with SV40 large T antigen express ed in the heart-forming region. Ultrastructure analysis by transmission ele ctron microscopy showed the primitive, precontractile nature of the resulti ng cells, with the absence of myofilaments, Z lines, and intercalated disks . Immunohistochemistry, RT-PCR, Northern blots, and oligonucleotide microar rays were used to determine the expression levels of thousands of genes in the 1H and ECL-2 cell lines. The resulting gene-expression profiles showed the transcription of early cardiomyocyte genes such as Nkx2.5, GATA4, Tbx5, dHAND, cardiac troponin C, and SM22-alpha. Furthermore, many genes not pre viously implicated in early cardiac development were expressed. Two of thes e genes, Hic-5, a possible negative regulator of muscle differentiation, an d the transcription enhancing factor TEF-5 were selected and shown by in si tu hybridizations to be expressed in the early developing heart. The result s show that the 1H and ECL-2 cell lines can be used to discover novel genes expressed in the early cardiomyocyte. (C) 2001 Academic Press