Submitted to: Biology of Reproduction
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/2/1999
Publication Date: N/A
Interpretive Summary: Previous studies indicate that when fetuses are crowded within the uterus of the pig, fetal losses occur during the same period as the generation of the fetal blood supply. Small fetuses, which are the most at risk to be lost, were also shown to have low hematocrits during this period. Thus, improvements in red blood cell development during this period will likely lead to decreased fetal loss in pigs carrying large litters. Folates are vitamins that are required for cells to synthesize DNA. Rapidly dividing cells, such as those of the developing conceptus and red blood cell precursors, are the most sensitive to folate deficiency. Improvements in folate transport will likely lead to improved conceptus development and improved red blood cell formation, particularly in small fetuses. Finally, we recently showed that a protein secreted by the uterus, a folate binding protein, is likely to be the main route of transfer of folate to the developing swine conceptus. To further characterize this protein and the mechanism of folate transfer, in the current study, two cDNAs representing the amino acid coding sequences for folate binding proteins were isolated and characterized. One was shown to correspond to the folate binding protein produced by the uterus. The other was shown to be a folate receptor. Both proteins are likely to be involved in folate delivery to the fetus. Knowledge of the factors controlling folate delivery to the conceptus will provide
Technical Abstract: Two distinct forms of endometrial folate binding protein (FBP) cDNAs were isolated using reverse transcription, polymerase chain reaction and 3' and 5' Rapid Amplification of cDNA Ends (RACE) procedures. The two forms encode secreted and membrane-bound forms of FBP. The cDNAs for both forms were heterogeneous in their 5' untranslated regions (UTR), suggesting differential splicing. The cDNAs for the secreted and membrane forms encoded 252 and 249 amino acid proteins, respectively; that were 73% identical and were 66 to 82% identical with other known folate binding proteins. Northern blots of endometrial total RNA probed with a secreted FBP specific probe indicated that mRNA concentrations do not change during early pregnancy. In contrast, blots probed with a membrane FBP specific probe indicated that mRNA concentrations increase dramatically from day 15 to day 24 of pregnancy. Finally, N-terminal amino acid sequencing of folate binding protein purified from day 15 pregnant uterine flushings matched the secreted form of FBP mRNA. These data are consistent with a role for secreted and membrane bound forms of folate binding proteins in the transport of folate to the developing swine conceptus during early pregnancy.