DIFFERENTIAL EXPRESSION OF I-SK MESSENGER-RNAS IN MOUSE-TISSUE DURING DEVELOPMENT AND PREGNANCY

The molecular isoform of the cDNA clone I-sk present in the AT-1 atrial tumor cell line was characterized by molecular cloning of I-sk cDNA. Since I-sk mRNA was found in mouse heart, kidney, and uterus, a complete study of its expression during development in the heart and kidney was performed, in addition to its expression in the uterus during pregnancy. In the heart, I-sk showed a 4-fold upregulation during the perinatal period followed by a 20-fold decrease between birth and the adult state. Furthermore, the two 0.9- and 3.4-kb transcripts were differentially regulated after birth. In the kidney, I-sk progressively increased 10-fold, reaching steady-state adult values at 21 days. I-sk mRNA levels in the uterus increased threefold at late pregnancy and decreased sixfold rapidly after birth. The I-sk gene is differentially expressed during development in kidney and cardiac tissue, and both I-sk transcripts appeared to be differentially regulated. Furthermore, the drastic changes in transcript levels before delivery and after birth suggest that I-sk plays a significant role in myometrium during late pregnancy and delivery.