|Keller, Madeline - CO STATE UNIV, FT COLLINS|
|Seidel Jr, George - CO STATE UNIV, FT COLLINS|
Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: April 28, 1998
Publication Date: N/A
Interpretive Summary: In cattle, nearly 20% of pregnancies fail between Days 7 and 16 of pregnancy. A likely period for embryonic loss to occur is when spherical or elliptical embryos, generally still less than 1 mm in diameter on Day 13 of pregnancy, elongate to more than 100 times that length by Day 16. A substantial portion of embryonic loss during this period probably is due to physiological alterations resulting in discord between the uterus and embryo. However, the molecular and cellular mechanisms regulating embryonic growth during this stage are not known. As a first step in determining the role that insulin-like growth factor (IGF) binding proteins (BPs) may have in regulating embryonic elongation in cattle, the type and relative abundance of IGFBPs were characterized in embryos and in serum, uterine tissues, and uterine fluid from pregnant and nonpregnant cows on Days 13 and 15 of the cycle. Results indicate that uterine and serum samples contained at least 5 of the 6 or more known IGFBPs, but these proteins were not made by embryos. The amount of certain IGFBPs found in the uterus varied between Day 13 and 15 of the cycle and was different in pregnant and nonpregnant cows. Because IGFBPs are known to regulate the proliferation and function of cells in other tissues of the body, these proteins may also be important in synchronizing uterine function with embryonic development during early embryonic elongation.
Technical Abstract: As a first step in determining the role that insulin-like growth factor (IGF) binding proteins (BPs) may have in regulating initial stages of embryonic elongation in cattle, the type and relative abundance of IGFBPs in serum, uterine tissues, and uterine fluid from pregnant and noninseminated cows on Days 13 and 15 post-estrus and Day 15 embryos were evaluated. Uterine and serum samples contained IGFBP-2, -3, -4, and -5. Compared with uterine and serum samples, IGFBPs in embryos and embryo- conditioned culture media were only faintly detectable. Percentage of total IGF-I binding activity attributed to IGFBP-3 was greater (p<.05) in myometrium, serum, and uterine fluid (>50%) than endometrium (40%) and caruncle (37%). Percentage of total binding attributed to IGFBP-2 was greater (p<.05) in caruncle, endometrium, and serum (approx. 30%) than in myometrium (16%) and uterine fluid (9%). Relative amount of certain IGFBPs varied between Day 13 and 15 post-estrus or pregnancy status. Concentrations of IGF-I in serum were greater (p<.05) in nonpregnant than pregnant cows. Concentration of IGF-I in uterine fluid did not differ due to pregnancy status or stage of cycle. All three uterine tissues, but not in embryos, contained mRNAs for IGFBP-1, -2, -3, -4, and -5. In situ hybridization indicated that IGFBP-1 mRNA was primarily localized in the luminal epithelium of the endometrium; IGFBP-2 mRNA was in the luminal epithelium and dense stromal cells adjacent to the endometrial epithelium; and IGFBP-3 mRNA was in vascular endothelial cells and was more prevalent in myometrium than endometrium. Tissue specificity and changes in abundance of IGFBPs in the uterus during early embryonic elongation indicate the potential importance of IGFBP regulation of uterine IGFs during this stage.