Temporal and spatial regulation of a gene expressed during rat heart maturation • 123

Abstract

Structural development and functional maturation in the rat heart occur over a short period of time between the 10th day of gestation and the third postnatal week. Researchers have been actively attempting to identify and characterize genes that are likely to be important in this process. We have used differential display for this purpose, comparing the mRNAs expressed in the outflow tract of the heart on day 12 of embryonic development to those in the early postnatal aorta of the rat. One of the differentially displayed products was subcloned into pBluescript for sequencing and probe generation. Total RNA was harvested from rat hearts at various developmental ages, and RNA from multiple tissues was harvested from adult rats; the RNA was electrophoresed through agarose gels and transferred to nylon membranes for northern analysis. By northern analysis, this fragment hybridizes to a single 2 kilobase transcript present abundantly in the heart, kidney, and brain of adult rat tissues, while it is barely detectable in liver and spleen, and undetectable in lung. A single transcript of identical size is detected at low levels in RNA from rat heart of day 14 to 20 of embryonic development, after which the abundance increases significantly to a maximum during the first postnatal week, reaching an intermediate level similar to the adult by the third postnatal week. A digoxigenin-tagged antisense riboprobe was synthesized and hybridized specifically to the atrioventricular canal and outflow tract regions of the heart of day 12 embryonic rats, as well as to the brain by in situ hybridization. Sequence analysis of the cloned fragment reveals significant homology to the 3′ untranslated region of an alpha integrin cloned from human and mouse sources. The transcript size of these known integrins are almost 4 kilobases, suggesting that the gene we are studying is likely to be novel. Its tissue-specific and developmentally regulated expression pattern, as well as its homology to a member of the integrin family of cell-surface receptors suggest that it may have a role in heart maturation. Cloning of this gene will facilitate determination of its function.