Overexpression of beta-subunit of thyroid-stimulating hormone in Meishan swine identified by differential display

Administration of thyroxine affects the morphometric parameters and VEGF expression in the uterus and placenta and the uterine vascularization but does not affect reproductive parameters in gilts during early gestation

The aim of this study was to evaluate the effects of thyroxine administration on morphometric parameters, expression of vascular endothelial growth factor (VEGF) and vascularization in the uterus and placenta and reproductive parameters in gilts at 70 days of gestation. At 150 days of age, i.e., before first heat, 20 gilts were randomly divided into two experimental groups: treated (n=10) and control (n=10). The treated group received a daily dose of 400 μg of L-thyroxine (T(4)) in their diet until slaughter and the control group received only typical meals. Before artificial insemination, blood was collected to determine plasma total T(4). The gilts were inseminated in the second oestrus and slaughtered at 70 days of gestation. The foetal thyroid follicular epithelium height, number, size and weight of foetuses; foetal myogenesis, corpora lutea number, embryonic mortality rate, uterine weight, placental weight and placental fluid volume were measured. Histomorphometric and immunohistochemical analysis of uterus and placenta were determined. The averages of all variables were compared by the Student's t-test. The gilts treated with thyroxine showed significant increase of plasma total T(4). At 70 days of gestation, the heights of the trophoblastic epithelium, endometrial epithelium and endometrial gland epithelium were significantly higher in the group treated with T(4). The expression of cytoplasmatic and nuclear VEGF in trophoblastic cells and the number of blood vessels per field in endometrial stroma were significantly higher in the gilts treated with T(4). No other significant differences between groups were obtained with respect to other parameters (p>0.05). We conclude that oral administration of T(4) up to 70 days of pregnancy in gilts affects the morphometric parameters, the expression of placental VEGF and the uterine vascularization but does not affect reproductive parameters in gilts during early gestation.

Breed differences in clearance of porcine FSH in hypophysectomized rats

Extracts of anterior pituitary (AP) glands were infused i.v. into hypophysectomized male rats followed by sequential sampling of blood for 120 min. Determination of follicle-stimulating hormone (FSH) concentrations established that FSH from Chinese Meishan males decreased in the circulation of rats more slowly than FSH in extracts of AP from crossbred occidental pigs (P<0.003). Additionally, FSH from AP extracts of castrated males disappeared somewhat more slowly (P<0.06) than FSH from extracts of boars. Evaluation of FSH by bioassay and radioimmunoassay yielded similar concentrations in AP from Meishan and crossbred boars. Serum testosterone concentrations increased with time through 90 min after infusion of AP, but the rate of increase of testosterone was not related to amount of luteinizing hormone (LH) that was administered indicating LH receptor saturation. Unexpectedly, the rate of increase in testosterone was more rapid with AP extracts from boars than with extracts from castrated males. Observations from the current study imply structural alterations of FSH in the AP of Meishan males relative to crossbred males allowing sustained concentrations in the circulation, and this FSH possesses similar activation of the FSH receptor. The amount of LH in the AP extracts saturated the LH receptors of the hypophysectomized male rats, but some factor in extracts of boars differed from those of castrated males.

Evaluation of gene expression in pigs selected for enhanced reproduction using differential display PCR: II. Anterior pituitary

The objective of this study was to identify differentially expressed genes in the anterior pituitary (AP) of sows selected for enhanced reproductive phenotypes. Selection in the Index (I) line was based on an index of ovulation rate and embryo survival, whereas random selection was used in the Control (C) line. Average numbers of fully formed piglets at birth were 12.5 +/- 1.5 and 9.9 +/- 2.0 for Line I and C sows used in this study, respectively. In order to induce luteolysis and synchronize follicle development, sows were injected (i.m.) with 2 mL of prostaglandin F2alpha analog between d 12 and 14 of the estrous cycle. Tissue was harvested 2 d (d2) or 4 d (d4) after injection, resulting in four experimental groups: Cd2 (n = 6), Cd4 (n = 4), Id2 (n = 6), and Id4 (n = 7). Differential display PCR (ddPCR) was used to search for transcriptional changes between selection lines in the AP, using samples within line but pooled across days. Northern hybridization was used to confirm ddPCR results. For ddPCR, two pools were used from each line (C and I). Three genes were confirmed to be differentially expressed between Lines I and C: G-beta like protein, ferritin heavy-chain, and follicle stimulating hormone beta subunit, whereas many other expressed sequence tags were observed to be differentially expressed but still require confirmation. Our findings indicate that long-term selection to increase ovulation rate and decrease embryo mortality has altered transcriptional patterns in the anterior pituitary, most likely as correlated responses.

EST-based gene discovery in pig: virtual expression patterns and comparative mapping to human

A molecular understanding of porcine reproduction is of biological interest and economic importance. Our Midwest Consortium has produced cDNA libraries containing the majority of genes expressed in major female reproductive tissues, and we have deposited into public databases 21,499 expressed sequence tag (EST) gene sequences from the 3' end of clones from these libraries. These sequences represent 10,574 different genes, based on sequence comparison among these data, and comparison with existing porcine ESTs and genes indicate as many as 4652 of these EST clusters are novel. In silico analysis identified sequences that are expressed in specific pig tissues or organs and confirmed the broad expression in pig for many genes ubiquitously expressed in human tissues. Furthermore, we have developed computer software to identify sequence similarity of these pig genes with their human counterparts, and to extract the mapping information of these human homologues from genome databases. We demonstrate the utility of this software for comparative mapping by localizing 61 genes on the porcine physical map for Chromosomes (Chrs) 5, 10, and 14.

Neonatal Meishan pigs show POU1F1 genotype effects on plasma GH and PRL concentration

Chinese Meishan pigs develop rapidly with onset of puberty at less than 100 days of age, and have a smaller placental size and larger litter size as compared with British/Continental breeds. POU1F1 is a member of the POU-domain family gene and is a positive regulator for growth hormone (GH), prolactin (PRL), and thyroid-stimulating hormone beta (TSHbeta) in several mammalian species. To investigate the role of POU1F1 in controlling pig growth and reproduction traits, Meishan (MS) pigs segregating a MspI POU1F1 polymorphism were used to determine differences of GH and PRL at both mRNA and circulating hormone concentrations. Animals from nine litters were used to collect pituitary (n=60) and/or blood samples (n=80) at day 0, 15, and 30 after birth, and all animals were genotyped (CC, CD, DD) for the MspI POU1F1 polymorphism. Reverse transcriptase-polymerase chain reaction (RT-PCR) with standard curve quantification was used to quantify mRNA levels for GH, PRL, and two alternative POU1F1 transcripts, POU1F1-alpha, and POU1F1-beta. Radioimmunoassays were done to determine the circulating concentration of GH and PRL in blood plasma. Our results indicated a significant effect of POU1F1 genotype on circulating levels of both GH and PRL at birth, but not thereafter. The DD neonates had lower levels of GH, but higher levels of PRL, than other genotypes. POU1F1-alpha mRNA decreased (P<0.05) from days 0 to 30, which paralleled decreases (P<0.05) in GH mRNA as well as PRL and GH plasma levels over the same period. POU1F1-beta mRNA levels did not significantly change over this period. Correlations were significant between POU1F1-alpha mRNA and both GH mRNA and GH plasma concentration levels, as well as between the two POU1F1 mRNA isoforms. Results from this study add to our understanding of the role of POU1F1 in controlling pig development and reproduction.

Identification of genomic regions controlling plasma FSH concentrations in Meishan-White Composite boars

The Chinese Meishan (ME) breed of pig is unique for many reproductive traits. Compared with Western breeds of swine, ME females reach puberty earlier, ovulate more ova per estrus, and have greater uterine capacity, while intact males (boars) have smaller testes and extremely elevated plasma levels of pituitary-derived glycoprotein hormones. In an effort to identify the genetic mechanisms controlling the elevated plasma levels of pituitary-derived glycoprotein hormones [in particular, follicle-stimulating hormone (FSH)] and to determine whether some of these genetic factors are also responsible for differences in other phenotypes, we scanned the entire genome for regions that affected plasma FSH in boars from a Meishan-White Composite (equal contributions of Chester White, Landrace, Large White, and Yorkshire) resource population. Initially, the entire genome of 121 boars was scanned for regions that potentially influenced plasma FSH. The most significant genomic regions were further studied in a total of 436 boars. Three genomic regions located on chromosomes 3, 10, and X apparently possess genes that significantly affect FSH level, and one region provided suggestive evidence for the presence of FSH-controlling genes located on chromosome 8. The region on the X chromosome also affected testes size. Similar genomic regions to those identified on chromosomes 3, 8, and 10 in this study have been identified to affect ovulation rate in female litter mates, supporting the hypothesis that plasma FSH in pubertal boars and ovulation rate in females is controlled by a similar set of genes.

Testicular morphology and function in boars differing in concentrations of plasma follicle-stimulating hormone

The objective of this study was to evaluate morphological characteristics and testicular function of boars with different endogenous concentrations of FSH. Boars were selected at 6 mo of age on the basis of mean FSH concentrations in plasma collected at 4, 5, and 6 mo of age. Boars were classified within half-sibling families based on whether they had high concentrations of FSH (HiFSH, > 500 ng/ml, n = 9) or low concentrations (LoFSH, < 500 ng/ml, n = 7). At 14.5 mo, testes were collected, fixed, sectioned at 1 microm, and evaluated for morphological characteristics. Boars with LoFSH had larger (p < 0.01) testicular and epididymal weights than boars with HiFSH, greater (p < 0.01) daily sperm production per gram of testis, and greater total daily sperm production per boar. Testes of boars with LoFSH had a greater (p < 0.03) volume percentage of seminiferous tubules, a lesser percentage (p < 0.03) of Leydig cells, and a somewhat lesser (p = 0.06) percentage of vascular structures than testes of boars with HiFSH. Testes of boars with LoFSH had greater (p < 0.01) total tubule volume and tubule length than testes of boars with HiFSH. There were no differences (p > 0.70) in volume, diameter, or total number of Leydig cells or in total interstitial volume in testes (p > 0.41) of these two groups. Production of testosterone in vitro per paired testis and per million Leydig cells was not different (p > 0.65) between boars with HiFSH or LoFSH. Greater concentrations of FSH in blood plasma were negatively associated with development of seminiferous tubules and spermatogenic efficiency, whereas Leydig cell development was not different in boars of these two groups.

Positive association between expression of follicle-stimulating hormone beta and activin betaB-subunit genes in boars

This study tested our hypothesis that inhibin/activin (I/A) betaB subunit and not follistatin (FS) gene expression relates positively to plasma FSH concentrations in the anterior pituitary gland of boars. Mature crossbred boars (n = 12) were selected for divergence in plasma FSH concentrations, and their anterior pituitary glands were evaluated for expression of the FSHbeta, I/A ssB, FS, calmodulin, and GnRH receptor (GnRH-R) genes by semiquantitative reverse transcription-polymerase chain reaction (RT-PCR) and/or RNase protection assays (RPAs). Expression of I/A ssB was greater (p < 0. 01) in the six boars with high FSH than in the six with low FSH; expression of the I/A betaB-subunit gene was positively correlated to that of the FSHbeta gene (RT-PCR: r = 0.96; p < 0.01; RPA: r = 0.68; p < 0.05). In contrast, expression of the FS (p > 0.10), GnRH-R (p > 0. 08), and calmodulin (p > 0.10) genes was similar in the two groups of boars. Additionally, expression of the FSHbeta gene was correlated positively with pituitary and plasma FSH concentrations (r = 0.69 and 0.88, respectively; p < 0.05). These results support the hypothesis that activin B is partially responsible for elevated FSH concentrations in boars. Furthermore, the expression difference of the calmodulin gene observed previously between Meishan and White Composite boars represents a breed difference unrelated to FSH.

Suppression of somatotroph function induced by growth hormone treatment in neonatal pigs

The effect of recombinant porcine growth hormone (pGH) treatment on pituitary function was evaluated in young pigs. Piglets received intraperitoneal recombinant pGH implants (0.5 mg/d sustained release) or vehicle implants beginning at 3 d of age. Ten piglets were sacrificed at 4 and 6 wk of age (five piglets/treatment group) for the collection of pituitary glands, blood, and liver tissue. Blood samples also were drawn at 3 and 12 d of age. Serum concentrations of GH, prolactin (PRL), thyroid-stimulating hormone (TSH), insulin-like growth factor-1 (IGF-1) and IGF-2 were evaluated. Levels of IGF-1 and IGF-2 mRNA were determined in liver samples. Treatment with GH increased circulating levels of GH and IGF-1 (P < 0.01), but not PRL, TSH, or IGF-2. Hepatic IGF-1, but not IGF-2, mRNA levels were increased by pGH (P < 0.001). Cultured pituitary cells from each animal were challenged with 0.1, 1, and 10 nM GH-releasing hormone (GHRH); 2 nM 8-Br-cAMP; or 100 nM phorbol myristate acetate. The release of GH from cultured pituitary cells was stimulated by all secretagogues (P < 0.001). The secretion of GH, but not PRL or TSH, in culture was inhibited by previous in vivo GH treatment (P < 0.001). Similarly, cellular GH, but not PRL or TSH, content was lower in the GH-implant group (P = 0.005). Cell cultures from 6-wk-old piglets secreted more GH, but not PRL or TSH, than cultures from 4-wk-old piglets (P < 0.05). Likewise, cellular GH, but not PRL or TSH, content was greatest in cultures from 6-wk-old animals (P = 0.002). Piglet growth was not affected by exogenous GH treatment (P = 0.67). These results demonstrate that exogenous pGH treatment selectively down-regulates somatotroph function in young pigs.

Breed differences in expression of inhibin/activin subunits in porcine anterior pituitary glands

Chinese Meishan (MS) boars have greater plasma FSH concentrations than European White Composite boars, but this difference does not occur in females of these breeds. To understand this disparity, we studied expression of the follistatin gene and of genes for the inhibin/activin alpha-, beta A-, and beta B-subunits in porcine anterior pituitary glands using quantitative reverse transcription-PCR and ribonuclease protection techniques. We found that 1) the inhibin/activin beta A- and beta B-subunits and follistatin were expressed in porcine pituitary, 2) the alpha-subunit was not detected in the porcine pituitary, but was highly expressed in porcine follicles; and 3) the beta B-subunit gene is more abundantly expressed (2-fold greater) in MS boar pituitaries than in pituitaries of White Composite boars. We conclude that this is not due to a breed difference, because the expression levels of this gene were similar in pituitaries of females of these breeds. No breed differences were detected for other genes screened in this study. From these observations, we propose that activin B, a dimer of beta B-subunits and a stimulator of FSH secretion, may be partially responsible for the elevated plasma FSH concentrations in MS boars, and intrapituitary inhibin plays no or a very minimal role.