Study on intraocular expression of pituitary hormones possibly involved in the regulation of retinal development in the chicken

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We have demonstrated previously that immunoreactive α-melanocyte-stimulating hormone (α-MSH) and growth hormone (GH) are expressed in developing chicken retinas with developmentally regulated patterns. The major aim of the present study was to examine their expression and other pituitary hormones at transcriptional level. RT-PCR revealed that pituitary-specific transcription factor, Pit-1, was expressed in embryonic chicken neural retinas. The Pit-1-regulated hormones, such as prolactin (PRL), thyrotropin (TSH), GH, and their receptors were also found to be expressed. Since their expression levels in the neural retinas were very low when compared with those in the pituitary, it is possible that they act as local mediators to regulate ocular development. Pro-opiomelanocortin, a common precursor of melanocortin peptides and other peptide hormones, was expressed in the neural retinas as well as in retinal pigment epithelial (RPE) cells. Two prohormone convertases, PC 1 and PC2, were clone … More d and their specific primers were designed based on the sequences obtained in this study. Using the primers, we demonstrated that PC1 and PC2 were co-expressed in both the neural retinas and RPE cells, supporting our previous finding that a MSH is expressed intraocularly. These findings suggest that neural retina is another site of pituitary hormone production during embryonic development in the chicken. Interestingly, we found for the first time that the chicken GH gene produces anti-sense-GH (GH-as) transcripts. Their transcription from the opposite strand of GH starts with downstream of the polyadenylation site of GH-sense mRNAs and ends with upstream of the TATA box for pituitary GH mRNA. More than 6 types of GH-as transcripts with different exon composition were identified. Since no open reading frames (ORFs) were detected in the GH-as transcripts, it is possible that they act as regulators of GH translation by interacting with GH-sense mRNAs though further analyses are required. We also performed additional analyses to clarify whether α-MSH has physiological roles, which may help us to study on the role of α-MSH in ocular development. Less