Mammalian mesotocin: cDNA sequence and expression of an oxytocin-like gene in a macropodid marsupial, the tammar wallaby.
The oxytocin (OT)-like peptide of most Australian marsupials is mesotocin (MT), which differs from OT by substitution of isoleucine for leucine at position 8. To date, the only information on the evolution of the OT peptide in marsupials is based on the sequence of the 9-amino acid peptide itself. The main objective of this study was to obtain the nucleotide and derived amino acid sequences of a marsupial MT precursor for comparison with known OT and MT precursors of eutherians and nonmammalian vertebrates. The structural organization and sequence of the MT gene and its specific transcript were established in a macropodid marsupial, the tammar wallaby, using PCR strategies with a combination of genomic DNA and reverse-transcribed hypothalamic RNA. A consensus genomic sequence of 1221 bp was produced which, by comparison with the expressed cDNA sequence, included two intron sequences of 480 and 188 bp. The tammar MT precursor molecule consists of a 32-amino acid signal peptide, followed by the MT-encoding region and the Gly-Lys-Arg carboxy-terminal cleavage and amidation signal which separates the nonapeptide from the 92-amino acid neurophysin. At the amino acid level, the MT precursor is more similar to eutherian OT precursors than to nonmammalian MT, isotocin, or vasotocin precursors. Northern analysis demonstrated a single transcript of approximately 0.6 kB in the hypothalamus. Mesotocin mRNA is also present in several tissues of the reproductive tract, including the corpus luteum, follicle, uterus, and placenta. Within the ovary, MT transcripts are localized predominantly in the granulosa cells of antral follicles with some positive hybridization signals in cells of the theca interna. This pattern of MT gene expression in marsupials is very similar to that of OT in eutherians and suggests a conserved physiology in the mammalian ovary.
Parry
L J
LJ
Department of Zoology, University of Melbourne, Parkville, Victoria, Australia. 1.parry@hfi.unimelb.edu.au
Bathgate
R A
RA
Ivell
R
R
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D015152:Blotting, Northern; D018076:DNA, Complementary / Q000737:chemistry*; D005260:Female; D015870:Gene Expression; D017403:In Situ Hybridization; D007614:Macropodidae / Q000235:genetics*; D008969:Molecular Sequence Data; D010121:Oxytocin / Q000031:analogs & derivatives* / Q000235:genetics*; D011247:Pregnancy; D012333:RNA, Messenger / Q000032:analysis; D020133:Reverse Transcriptase Polymerase Chain Reaction; D017385:Sequence Homology
D018076:DNA, Complementary; D012333:RNA, Messenger; C001713:mesotocin; D010121:Oxytocin