Sulfated glycoprotein-1 (SGP-1) expression in ovine endometrium during the oestrous cycle and early pregnancy

This study determined effects of day of oestrous cycle and early pregnancy on sulfated glycoprotein-1 (SGP-1) expression in ovine endometrium. A 364-bp clone of the ovine SGP-1 mRNA was amplified from reverse transcribed Day-15 cyclic endometrial mRNA using the polymerase chain reaction (PCR) and primers specific for the rat SGP-1 mRNA sequence. Nucleotide sequence of the ovine SGP-1 cDNA shared significant identity with rat SGP-1 and human prosaposin. Ewes (n = 40) were hysterectomized on either Day 1, 6, 11, 13 or 15 of the oestrous cycle or on Day 11, 13, 15, 17 or 25 of early pregnancy. Total cellular RNA was isolated from endometrium and subjected to Northern and slot blot hybridization analyses using an antisense cRNA probe transcribed from the ovine SGP-1 cDNA clone. A single 2.6-kb mRNA transcript was detected by Northern hybridization analyses. Slot blot hybridization analyses indicated that steady-state levels of endometrial SGP-1 mRNA varied during the oestrous cycle (cubic, P < 0.02) and increased between Day 11 and Day 25 of early pregnancy (linear, P < 0.01). On Days 11, 13 and 15, endometrial SGP-1 mRNA levels were greater in pregnant ewes than in cyclic ewes (day x pregnancy status, P < 0.01). Immunohistochemical localization of SGP-1 in uterine tissues with rabbit anti-rat SGP-1 antibody revealed intense immunoreactivity associated primarily with the endometrial epithelium. These results indicate that the ovine endometrium expresses SGP-1, a prosaposin, and that SGP-1 expression varies during the oestrous cycle and is enhanced by the conceptus. The presence of SGP-1 in the endometrium suggests intracellular and extracellular roles for this protein in glycosphingolipid metabolism or transport in the uterine environment.