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JL Crawford and AS McNeilly
Associations between granins (secretogranin II (SgII) and chromogranin A and B (CgA and CgB)) and gonadotrophins (LH and FSH) have been reported in rodents and they may interact to facilitate differential storage and secretion of LH and FSH. This study investigated the relationship between granins and gonadotrophins in sheep at different stages of the oestrous cycle. Thirty-four cycling ewes had their oestrous cycles synchronised, and were divided into late luteal (LL; n=5) and early (EF; n=4), mid (n=3) and late (LF; n=11) follicular stages, and 24-53 h (n=5), 80-100 h (n=3) and 120-144 h (n=3) after the preovulatory LH surge (PS). LHbeta mRNA levels were low in LF ewes (when plasma levels and pulse frequency of LH were high) but had increased by 80-100 h PS. In contrast, FSHbeta mRNA levels decreased during the follicular phase and plasma FSH concentrations followed a similar pattern, to peak at 24-53 h PS due to low plasma oestradiol levels. While alpha-gonadotrophin subunit (alpha-GSU), SgII and CgA mRNA levels did not change, CgB mRNA levels were elevated in EF ewes and had declined in ewes around the surge. Four distinctly sized mRNA transcripts ( approximately 1.3, 2.0, 2.8 and 3.2 kb) were observed for CgA mRNA, while a double band was observed for LHbeta mRNA that was subsequently reduced to a single band after 3'-poly(A) tail truncation. The long and short LHbeta transcripts were prevalent in follicular and luteal ewes respectively. Numbers of LH(+ve)/FSH(-ve) granules stored within gonadotrophs were not different in LL and LF ewes (even though proportions of LH(+ve) granules were higher in LF ewes), but were reduced at 24-53 h PS. The majority of LH(+ve) granules also contained SgII, although few CgA(+ve) granules were found. Granule partitioning was evident whereby FSH and CgA were located near the periphery, and LH and SgII throughout the matrix. In conclusion, increases in both storage of LH(+ve) granules and secretion of LH in LF ewes despite constant LHbeta mRNA levels was facilitated, at least in part, by improved LHbeta mRNA transcript stability. Fewer LH(+ve)/FSH(-ve) granules were in storage after the PS, which was mirrored by a reduction in LH pulsatile release. Surprisingly, in view of results in rodents indicating significant changes, SgII and CgA mRNA levels did not change over the oestrous cycle in sheep. Conversely, CgB mRNA levels decreased around the time of PS. These novel results illustrate major differences in granin-gonadotrophin interactions between sheep and rodents.
JL Crawford, RJ Currie, and AS McNeilly
The pattern of replenishment of LH secretory granule stores in sheep pituitary gonadotrophs, after an induced LH surge, was determined by immunogold localisation at the ultrastructural level by electron microscopy. Twenty-four Welsh Mountain ewes were initially synchronised with progestagen devices for 14 days before luteolysis was induced by a prostaglandin F(2 alpha) analogue, cloprostenol. A further 24 h later, a preovulatory LH surge was induced by intravenous injection of a GnRH agonist, buserelin. Animals were divided into four groups (n=6) and blood sampled at 2 h intervals from 4 h prior, to 18 h after, buserelin administration and then at infrequent intervals (1 to 8 h) thereafter until death. Pulse profiles of LH were also obtained by an additional collection of blood samples within a 6 h window directly preceding death. Groups of animals were killed at 24, 48, 72 or 96 h after buserelin treatment. Pituitaries were dissected and processed for transmission electron microscopy and frozen for later molecular biological analysis. A characteristic preovulatory surge of LH was observed in all animals. The cytoplasm of gonadotrophs, in animals killed 24 h after buserelin treatment, was completely empty of secretory granules. This was associated with diminutive pituitary LH content, low pituitary GnRH binding levels and an almost complete absence (one pulse in one animal) of LH pulsatile secretion. Despite the lack of apparent secretory activity, clusters of exposed LH beta label present within the cytoplasm at this time and constant LHbeta mRNA expression levels irrespective of tissue collection time, suggest that the cell is actively synthesising LHbeta. The formation of sparse numbers of small LH beta immuno-labelled electron-dense secretory granules was apparent at 48 h after buserelin treatment, and replenishment of LH beta immuno-labelled granule stores continued until total granule numbers had increased two-fold (P<0.01) by 96 h post-treatment. Affiliated with granule replenishment was a significant increase in pituitary LH content (P<0.01), pituitary GnRH binding levels (P<0.01) and the restoration of LH pulsatile secretion. Despite the replenishment of granule stores with time, cytoplasmic area did not vary. These results suggest that restoration of pulsatile LH secretion after a preovulatory LH surge is related to replenishment of LH beta secretory granule stores and an increase in GnRH binding levels.
L Nicol, McNeilly JR, M Stridsberg, JL Crawford, and AS McNeilly
The granin proteins secretogranin II (SgII) and chromogranin A (CgA) are commonly found associated with LH and/or FSH within specialised secretory granules in gonadotroph cells, and it is possible that they play an important role in the differential secretion of the gonadotrophins. In this study we have examined the regulation of the biosynthesis and secretion of SgII and CgA, in relation to LH secretion, in the LbetaT2 mouse pituitary gonadotroph cell line. Three experiments were carried out to investigate the effects of oestradiol (E2) and dexamethasone (Dex) in the presence and absence of GnRH (experiment 1), differing GnRH concentrations (experiment 2) and alterations in GnRH pulse frequency (experiment 3). In experiment 1, exposure to E2, Dex or E2+Dex, either with or without GnRH treatment, resulted in increased LH secretion. Steroids alone had no effect on LHbeta mRNA levels, but in the presence of GnRH LHbeta mRNA levels were increased in Dex- and E2+Dex-treated cells. GnRH receptor (GnRH-R) mRNA levels were up-regulated by Dex and E2+Dex, but were unaffected by GnRH. There were no steroid-induced changes in SgII or CgA mRNA, but increased levels of CgA mRNA were observed after GnRH treatment in cells cultured in the presence of Dex. In experiment 2, increasing concentrations of GnRH resulted in increases in LH secretion that were inversely dose-dependent. No changes in LHbeta, GnRH-R or SgII mRNA levels were observed, but there were dose-dependent increases in CgA mRNA levels. In experiment 3, GnRH was given as either 1 pulse/day or 4 pulses/day for 3 days. Both pulse regimes resulted in increased LH, SgII and CgA secretion compared with controls during the first 15 min pulse on day 3. Exposure to GnRH at 4 pulses/day increased LH and SgII secretion compared with controls during all 4 pulses, but secretion of both proteins was reduced during pulses 2-4 compared with pulse 1. CgA secretion also increased due to GnRH in pulse 1, but was decreased by GnRH treatment during pulse 2, and unchanged by GnRH during pulses 3 and 4. Total daily secretion of LH and SgII from cells given 1 pulse/day of GnRH increased compared with controls on all three treatment days, while total CgA secretion increased in response to GnRH on days 2 and 3 only. Intracellular levels of SgII, but not LH, decreased after GnRH treatment. In contrast, intracellular CgA was increased, but only after 4 pulses/day of GnRH. Levels of LHbeta, but not SgII, mRNA were increased by both pulse regimes, while CgA mRNA levels increased after 1 pulse/day of GnRH. These results indicate that there is a close correlation between the GnRH-stimulated release of LH and SgII from LbetaT2 cells, suggesting that SgII may have an influential role in the regulated secretion of LH, possibly by inducing LH aggregation to facilitate trafficking into secretory granules. CgA secretion does not appear to be closely associated with that of LH, but CgA expression does appear to be regulated by GnRH, which may indicate involvement in the control of LH secretion, possibly by influencing the proportion of LH in the different types of secretory granules.
CJ Souza, C MacDougall, BK Campbell, AS McNeilly, and DT Baird
Genetic variations in ovulation rate which occur in different breeds of sheep provide useful models to explore the mechanisms regulating the development of antral follicles. The Booroola gene, an autosomal mutation that affects ovulation rate, has been known for over two decades and despite intensive research it has not yet been identified. Using resources from human genome mapping and known data about gene linkage and chromosome location in the sheep, we selected the gene encoding the Bone Morphogenetic Protein receptor (BMPR) type 1 B (ALK-6) as a candidate site for the mutation. The BMPR1B gene in the human is located at the region linked with the Booroola mutation, syntenic to chromosome 6 in the sheep. A fragment of the sheep BMPR1B gene was cloned from an ovarian cDNA and the deduced aminoacid (AA) sequence is over 98% homologous to the known mammalian sequences. cDNA and genomic DNA from 20 Booroola genotypes were screened and two point mutation were found in the kinase domain of the receptor, one at base 746 of the coding region (A in the ++ to a G in FF animals) which results in a change from a glutamine in the wild type to a arginine in the Booroola animals. Another point mutation was identified at position 1113, (C to A) but this mutation does not change the coding aminoacid. The first mutation was confirmed in genomic DNA from 10 ewes from an independent Brazilian flock which segregates the Booroola phenotype. In all instances homozygous FecB gene carrier (n=11) had only the 746 A to G mutation, non gene carriers (n=14) had only the wild type sequence and heterozygote gene carriers (n=5) had both sequences. This mutation in the subdomain 3 of the kinase domain could result in an alteration in the expression and/or phosphorylation of SMADs, resulting in the phenotype characteristic of the Booroola animals which is the 'precocious' development of a large number of small antral follicles resulting in increased ovulation rate.
Davis JR, RF McMahon, PR Lowenstein, MG Castro, GA Lincoln, and AS McNeilly
Gene therapy for pituitary disease requires evaluation for safety as well as efficacy. We have reported results of adenovirus-mediated gene transfer using the sheep as a large animal model that allows longitudinal evaluation of hormone secretion and have confirmed high levels of transgene expression up to 7 days after direct stereotaxic injection into the pituitary gland. Here we report the results of detailed histological examination of the pituitary glands from animals injected with two recombinant adenoviruses expressing the beta-galactosidase marker gene, or with saline vehicle to control for the potential tissue-disruptive effect of the injection volume itself. Pituitaries injected with saline showed no evidence of inflammatory response apart from occasional minor foci of apoptosis. In all other respects they were indistinguishable from normal uninjected control pituitary glands. Glands injected with recombinant adenoviruses containing either the hCMV-beta-gal or the hPRL-beta-gal transgene, on the other hand, displayed variable degrees of inflammatory response, with periglandular fibrosis, lymphocytic infiltrate and venulitis in almost all cases. Focal necrosis and/or apoptosis was noted in six of nine cases. In summary, we have found evidence of severe inflammatory reaction within the first seven days of adenovirus injection, amounting to significant hypophysitis. The histological extent of this reaction has not previously been recognised by studies of the efficacy of gene transfer in rodents, and was underestimated by immunocytochemical studies of hormone and transgene expression. The findings emphasise the need for careful evaluation of the safety of endocrine gene therapy, and for caution with the dose of vector used.
KJ Turner, S Macpherson, MR Millar, AS McNeilly, K Williams, M Cranfield, NP Groome, RM Sharpe, HM Fraser, and PT Saunders
The biosynthesis of oestrogens from androgens is catalysed by the aromatase complex, an essential component of which is the aromatase cytochrome P450 (P450 arom) protein. Expression of a functional P450 arom is essential for normal fertility in males and females and the sequence of the protein is highly conserved. We have raised a new monoclonal antibody against a conserved peptide and validated it on fixed tissue sections of the rat, common marmoset (Callthrix jacchus) and human. The monoclonal antibody was used successfully for Western analysis and specifically reacted with a 55 kDa protein in microsomal extracts. On sections of ovaries in all three species, expression in follicles was specific to the mural granulosa cells of antral follicles and was present in corpora lutea. In the human and marmoset, staining of luteal cells was markedly heterogeneous and did not appear to vary consistently with the stage of the cycle. The intensity of immunostaining was elevated in corpora lutea from pregnant rats and following human chorionic gonadotropin rescue in the human. In the testis, the highest levels of expression were observed in the Leydig cells within the interstitium. In adult rat and marmoset, and possibly also in the human, some P450 arom was associated with the cytoplasm surrounding elongate spermatids but other germ cells were immunonegative. In conclusion, a new monoclonal antibody specific for P450 arom recognises the protein in rodent, primate and human. Its ability to work on fixed tissue sections will facilitate identification of individual cells expressing P450 arom within complex tissues.