Molecular mechanisms of oviposition control

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We have proposed a hypothesis for oviposition mechanism as follows ; ovarian prostaglandin is released into peripheral plasma to stimulating uterine contractions, which in turn, triggers AVT release from the neurohypophysis. The present project was conducted to prove the above hypothesis by providing following evidence on the molecular basis.1. Prostaglandins were produced in the theca layers of the largest pre- and postovulatory follicles and tissue PG level was highest with concurrent increase in plasma PGF concentration immediately before oviposition. Ovarian-oviposition inducing factor was identified as PG by HPLC analysis. These results indicate that ovarian PG plays a pivotal role in the regulation of oviposition.2. Plasma AVT concentration also increased at the time of oviposition. AVT was released in response to uterine contractions but this increase was suppressed by indomethacin treatment which delayed oviposition. Immunocytochemical studies revealed that AVT-containing neuro … More ns were detected at the preoptic region and superficial area of the third ventricle. AVT cDNA was cloned and its base sequence was determined. Using the 562-base cDNA as a probe Northern hybridization analysis detected about 700 bases of AVT mRNA in the hypothalamus. The mRNA levels increased 4-fold after 4-day of water deprivation. Analysis of in situ hybridization revealed AVT mRNA localized in the periventricular nuclei of the hypothalamus.3. Finally, the project of cloning of AVT receptor cDNA is stil in progress but solubilized fraction of AVT receptor of the chicken uterus was purified, electophoresed and this fraction was isolated. At present, amino acid sequencing is under an investigation and will be used for primers in PCR cloning to isolate the gene. On the basis of amino acid sequences of homologous region of human oxytocin receptor cDNA and rat arginine vasoporessin receptor, primers were synthesized for RT-PCR of chicken uterus RNA. The 452-bases RT-PCR cDNA product was used as a probe for Northern hybridization of the chicken uterus. Hybridizable mRNA species of 5.6, 4.6 and 2.1 kd were identified as AVT receptor mRNA. Less