A developmental switch in expression from blastocyst to endometrial/placental-type cytochrome P450 aromatase genes in the pig and horse.
Pig blastocysts exhibit a transient period of estrogen production at periimplantation, with a second, more sustained period of estrogen synthesis occurring in endometrium and placenta at later pregnancy. Previously we reported the isolation of cDNA clones encoding a novel isoform of cytochrome P450 aromatase (the terminal enzyme in the estrogen biosynthetic pathway) from porcine periimplantation blastocysts. The present study investigated pregnancy-associated expression, in blastocysts and maternal reproductive tract tissues of this and an additional mRNA transcript encoding a distinct P450 aromatase isoform. Restriction endonuclease and nucleotide sequence analyses of 44 cDNA clones demonstrated that the major aromatase mRNA in periimplantation blastocysts and early-pregnancy endometrium and placenta (blastocyst-type) differed in sequence from the major aromatase mRNA expressed in endometrium and placenta at midpregnancy (endometrial-type). The deduced blastocyst and endometrial aromatase isoform protein sequences had 93% similarity. A third type of aromatase mRNA, deleted in exons 4-6 sequences, also was cloned from blastocysts. This cDNA was identical in nucleotide sequence to the blastocyst full-length aromatase cDNA and specified an open reading frame of 354 amino acids for a putative aromatase-related protein containing the heme-binding domain. Expression of this shorter mRNA in blastocysts was confirmed by reverse transcription polymerase chain reaction. The 5'-untranslated exon sequences in the transcripts encoding the blastocyst-type aromatase isoform were distinct from that of the endometrial type, consistent with differential expression of multiple chromosomal genes. In periimplantation equine embryos, however, embryonic and placental 5'-untranslated exon-containing transcripts were coexpressed. Results identify an aromatase isoform expressed in the endometrium and placenta at midpregnancy, demonstrate a transition in synthesis of aromatase isoform-specific mRNAs during placental development, and suggest the preferential involvement of the blastocyst aromatase isoform in synthesis of estrogenic molecules that may function in embryo-maternal signaling at periimplantation.
Choi
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Department of Dairy and Poultry Sciences and the Interdisciplinary Concentration in Animal Molecular and Cell Biology, University of Florida, Gainesville 32611-0920, USA.
Collante
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Simmen
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Simmen
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FA
D000595:Amino Acid Sequence; D000818:Animals; D001141:Aromatase / Q000096:biosynthesis* / Q000235:genetics*; D001483:Base Sequence; D001755:Blastocyst / Q000201:enzymology*; D003001:Cloning, Molecular; D004717:Endometrium / Q000201:enzymology* / Q000254:growth & development; D005260:Female; D018507:Gene Expression Regulation, Developmental / Q000502:physiology*; D015971:Gene Expression Regulation, Enzymologic / Q000502:physiology*; D006736:Horses; D007527:Isoenzymes / Q000096:biosynthesis* / Q000235:genetics*; D008969:Molecular Sequence Data; D010920:Placenta / Q000201:enzymology*; D010929:Placentation; D016133:Polymerase Chain Reaction; D011247:Pregnancy; D012333:RNA, Messenger / Q000096:biosynthesis; D013552:Swine
D007527:Isoenzymes; D012333:RNA, Messenger; D001141:Aromatase