PORCINE CALBINDIN-D-9K GENE - EXPRESSION IN ENDOMETRIUM, MYOMETRIUM, AND PLACENTA IN THE ABSENCE OF A FUNCTIONAL ESTROGEN RESPONSE ELEMENT IN INTRON-A

The expression of Calbindin-D-9k (CaBP-9k) in the pig uterus and place nta was measured by Northern blot analysis and reverse transcription p olymerase chain reaction (PCR), respectively. Progesterone (P-4) admin istration to ovariectomized pigs decreased CaBP-9k mRNA levels. Expres sion of endometrial CaBP-9k mRNA was high on pregnancy Days 10-12 and below the detection limit on Days 15 and 18. On Day 60, expression cou ld be detected at low levels. In myometrium and placenta, CaBP-9k mRNA expression was not detectable by Northern analysis using total RNA. R everse-transcribed RNA from both tissues demonstrated the presence of CaBP-9k transcripts by means of PCR The partial CaBP-9k gene was ampli fied by PCR and cloned to determine the sequence of intron A, In contr ast to the rat CaBP-9k gene, the pig gene does not contain a functiona l estrogen response element (ERE) within this region. A similar ERE-li ke sequence located at the identical location was examined by gel reta rdation analysis and failed to bind the estradiol receptor. A similar disruption of this ERE-like sequence has been described in the human C aBP-9k gene, which is not expressed at any level in placenta, myometri um, or endometrium. It is concluded that the pig CaBP-9k gene is regul ated in these reproductive tissues in a manner distinct from that in r at and human tissues. The regulation is probably due to a regulatory r egion outside of intron A, which in the rat gene contains the key cis element for uterine expression of the CaBP-9k gene.