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  • Author: T A Yarney x
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Differences in properties of the sheep testicular LH and FSH receptors

T. A. Yarney and M. R. Sairam

ABSTRACT

Differences in binding and structural properties of ovine testicular FSH and LH receptors were investigated. The ovine FSH receptor did not discriminate between FSH of different species, although equine FSH was more reactive. In the same tissue, however, the LH receptor showed marked preference for ovine and bovine LH, reacting very weakly with other preparations of pituitary LH. Human chorionic gonadotrophin also reacted partly with the ovine LH receptor at 25 °C. However, at 4 °C. the optimum temperature for binding of the LH receptor to its homologous hormone, the receptor displayed no recognition for chorionic gonadotrophin preparations. Affinity cross-linking studies with ovine testicular membrane suggested that the ovine FSH receptor has an M r of 70 000, which is very similar to that observed in the porcine ovary. The M r of the ovine LH receptor was estimated to be 150 000, which is different from those of other mammalian species, including those that have been cloned. The data suggest that the binding and structural properties of the ovine FSH receptor are similar to those of other mammalian FSH receptors, whereas the ovine LH receptor appears to differ from other mammalian LH receptors in having a different M r and in being more stringent in its requirement for pituitary LH.

DOI:
https://doi.org/10.1677/jme.0.0060291
Volume 6: Issue 3,
Pages:
291–297 (7 total)
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Ontogeny of FSH receptor messenger ribonucleic acid transcripts in relation to FSH secretion and testicular function in sheep

T A Yarney, M H Fahmy, M R Sairam, H Khan, and E A Macdonald

ABSTRACT

The role of alternative splicing of the FSH receptor gene in the generation of FSH receptor proteins and testicular function remains an enigma. To address this issue, this investigation was conducted to determine variations in the expression of alternate FSH receptor mRNA transcripts in relation to changes in FSH release, hormone binding activity and testicular function during pubertal development of ram lambs from two genotypes of sheep (Romanov and a cross between Booroola × DLS) with different sexual precocity. Serum 17β-estradiol and testosterone concentrations were used as indices of Sertoli cell and testicular function. The results indicated that increases in Sertoli cell and testicular function normally seen during pubertal development are accompanied by age-dependent reductions in concentration of functional FSH receptors, as determined by binding of iodinated FSH to testicular membrane preparations. During the course of these changes, FSH release was either maintained at a steady level in Romanov lambs or it was gradually reduced in the Booroola × DLS cross, thus indicating that the testis had become more responsive to hormonal signal. This acquisition of heightened sensitivity was also associated with contrasting changes in the level of expression of FSH receptor mRNA transcripts. For both genotypes of sheep, 5 distinct species of mRNA transcripts of approximately 1·1, 1·5, 2·0, 2·5 and 6·5 kb were highly expressed from 11 to 22 weeks of age. Amongst these transcripts, the 1·1 kb molecular species was the most abundant. Specific probing for a previously cloned transcript called 151A1 representing the first 4 exons of the FSH receptor gene revealed a paradoxical increase in the level of expression from 11 weeks up to a maximum at 18-22 weeks of age for both genotypes. Collectively, the results indicated that contrasting changes in the production of specific alternatively spliced mRNA transcripts may mediate changes in FSH receptor expression which apparently accounts for the augmentation in sensitivity and function of the testis during pubertal development. Furthermore, the data provide the first important indication that the novel truncated transcript (151A1), which predictably encodes a soluble protein of either intra- or extracellular fate, could be physiologically relevant.

DOI:
https://doi.org/10.1677/jme.0.0180113
Volume 18: Issue 2,
Pages:
113–125 (13 total)