CALBINDIN-D-9K GENE-EXPRESSION DURING THE PERINATAL-PERIOD IN THE RAT- CORRELATION TO ESTROGEN-RECEPTOR EXPRESSION IN UTERUS

Calbindin-D-9k (CaBP-9k) is a cytosolic calcium binding protein mainly expressed in duodenum. placenta and uterus. The gene encoding the rat CaBP-9k is subject to tissue specific induction by 1.25 dihydrosyvita min D-3 (intestine) and estradiol (E(2)) (uterus). Control of placenta l expression remains unknown. The expression of CaBP-9k mRNA during th e perinatal period was studied (pregnancy day 21 (P21)-lactation day 4 (L4). In uterus, maximal expression levels were found at P21 and main tained until L1. With the transition to L2 the CaBP-9k mRNA concentrat ion dropped drastically below the detection limit as quantitated by No rthern blot analysis. Measurements of E(2) and progesterone (P) levels showed a gradual decrease at late pregnancy (P21: birth). Post partum E(2) levels continued to decline and P concentrations increased sligh tly. Uterine estrogen receptor (ER) mRNA levels determined by cDNA/PCR analysis revealed close correlation between expression of ER and CaBP -9k mRNAs, ER mRNA levels were maximal at P22 and declined at parturit ion and with onset of lactation. At L2 and L3 ER mRNA levels were mini mal and had decreased 5-fold compared to late pregnancy. CaBP-9k prote in concentrations fluctuated only slightly dependent on the stage of t he estrous cycle: estrus > proestrus > diestrus. During the perinatal period CaBP-9k concentration was overall lower than in non-pregnant ut erus and revealed only a moderate increase at birth and decrease in ea rly lactation. Similar to the uterine levels. placental CaBP-9k mRNA w as highest at P21 and remained high until birth. Fetal duodenal CaBP-9 k) rose sharply just prior to birth and plateaued in the early postpar tal period. In maternal duodenum, no significant changes of CaBP-9k mR NA were found in the perinatal period. We conclude that CaBP-9k is tis sue specifically regulated during the perinatal period and that in ute rus, expression is dependent on a critical amount of ER and E(2).