Intrinsic and extrinsic modulators direct pretranslational expression of preoptic regulatory factor 1 (porf-1) messenger RNAs.
Genes of the diffuse neuroendocrine system are often widely expressed. We are studying a newly discovered peptide gene, preoptic regulatory factor 1 (porf-1). In the rat, porf-1 has been shown to be a unique, single-copy gene. Although its exact function remains unknown, porf-1 encodes a gonadotropin-releasing hormone (GnRH) related sequence and we have previously shown that this gene is transcribed in the rat in a tissue-specific manner in the preoptic area of the hypothalamus and in the testis. In this report, we extend the tissue distribution studies. Because of their potential expression of a GnRH related peptide, we also assess the effects of testicular and pituitary factors on porf-1 transcripts. RNA from the medial basal (MBH) and preoptic areas (POA) of the hypothalamus, cerebral cortex, testis, and liver from intact, castrated, and hypophysectomized male rats is compared by Northern blot analysis. Three basic tissue-specific patterns are observed in the intact animal, one common to the three brain areas examined, one for testis, and one for liver. Hypophysectomy results in a substantial increase in a unique 0.68-kb hypothalamic porf-1 transcript which is not detectable in either the intact or the castrated rat. It also results in increased levels of a 0.9-kb transcript in the POA and MBH. This is consistent with a negative feedback effect of the pituitary on porf-1 gene expression in the brain. In contrast, castration does not have a substantial effect on porf-1 hypothalamic transcripts, although a slight increase is seen in levels of the 0.9-kb species in the cerebral cortex. However, two different mature transcripts are identified with region-specific cRNA probes in the testis, suggesting that there may be cell-type-specific porf-1 gene expression in this tissue. These transcripts are not altered by hypophysectomy. We also examine human RNA from four reproductive hormone producing and hormone responsive tissues. There are three separate patterns of human porf-1 related transcripts which are different from those seen in the rat, one in placenta, one in adrenal, and one common to testis and prostate. We conclude that alternative RNA formation is a strategy being used by the diffuse neuroendocrine system to diversify expression of the porf-1 gene in response to intrinsic cellular and extrinsic hormonal signals.
Nowak
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Department of Molecular and Cell Biology, The University of Connecticut, Storrs, Connecticut 06269-3125, USA.