cDNA sequence and expression of bovine prodynorphin

Genome-wide association study for calving performance using high-density genotypes in dairy and beef cattle

Background

Calving difficulty and perinatal mortality are prevalent in modern-day cattle production systems. It is well-established that there is a genetic component to both traits, yet little is known about their underlying genomic architecture, particularly in beef breeds. Therefore, we performed a genome-wide association study using high-density genotypes to elucidate the genomic architecture of these traits and to identify regions of the bovine genome associated with them.

Results

Genomic regions associated with calving difficulty (direct and maternal) and perinatal mortality were detected using two statistical approaches: (1) single-SNP (single nucleotide polymorphism) regression and (2) a Bayesian approach. Data included high-density genotypes on 770 Holstein-Friesian, 927 Charolais and 963 Limousin bulls. Several novel or previously identified genomic regions were detected but associations differed by breed. For example, two genomic associations, one each on chromosomes 18 and 2 explained 2.49 % and 3.13 % of the genetic variance in direct calving difficulty in the Holstein-Friesian and Charolais populations, respectively. Imputed Holstein-Friesian sequence data was used to refine the genomic regions responsible for significant associations. Several candidate genes on chromosome 18 were identified and four highly significant missense variants were detected within three of these genes (SIGLEC12, CTU1, and ZNF615). Nevertheless, only CTU1 contained a missense variant with a putative impact on direct calving difficulty based on SIFT (0.06) and Polyphen (0.95) scores. Using imputed sequence data, we refined a genomic region on chromosome 4 associated with maternal calving difficulty in the Holstein-Friesian population and found the strongest association with an intronic variant in the PCLO gene. A meta-analysis was performed across the three breeds for each calving performance trait to identify common variants associated with these traits in the three breeds. Our results suggest that a portion of the genetic variation in calving performance is common to all three breeds.

Conclusion

The genomic architecture of calving performance is complex and mainly influenced by many polymorphisms of small effect. We identified several associations of moderate effect size but the majority were breed-specific, indicating that breed-specific alleles exist for calving performance or that the linkage phase between genotyped allele and causal mutation varies between breeds.

Electronic supplementary material

The online version of this article (doi:10.1186/s12711-015-0126-4) contains supplementary material, which is available to authorized users.

The effect of testosterone and season on prodynorphin messenger RNA expression in the preoptic area-hypothalamus of the ram

Testosterone and season influence mRNA expression for the opioid, enkephalin, in the preoptic area and hypothalamus of rams. Dynorphin is another opioid which has been shown to play a role in the control of reproductive function in females. We now report effects of season and testosterone on the expression of prodynorphin mRNA in the hypothalamus of the ram. Castrated adult Romney Marsh rams (5/group) received vehicle or testosterone propionate (i.m.) during either the 'breeding' season or 'non-breeding' season. Prodynorphin mRNA expression was quantified in the hypothalami by in situ hybridisation. Testosterone treatment increased prodynorphin mRNA expression in the supraoptic nucleus and the bed nucleus of the stria terminalis in the breeding season but not during the non-breeding season. Prodynorphin mRNA expression was also higher in the breeding season than in the non-breeding season in the caudal preoptic area, paraventricular nucleus and accessory supraoptic nucleus, irrespective of treatment. No effects of treatment were observed in any other regions of the hypothalamus. We conclude that testosterone and season regulate prodynorphin mRNA expression in a region-specific manner, which may influence seasonal changes in reproductive function.

Distribution of preprodynorphin mRNA and dynorphin-a immunoreactivity in the sheep preoptic area and hypothalamus

Endogenous opioid peptides (EOP) are important modulators in a variety of neuroendocrine systems, including those mediating reproduction, energy balance, lactation, and stress. Recent work in the ewe has implicated the EOP, dynorphin (DYN), in the inhibitory effects of progesterone on pulsatile gonadotropin releasing hormone secretion. Although DYN is involved in a number of hypothalamic functions in the sheep, little is known regarding the localization of preprodynorphin (PPD) expression and its major product DYN A (1-17). In this study, we determined the distribution of PPD mRNA and DYN A-containing cell bodies in the brains of ovary-intact, luteal ewes. To detect PPD mRNA, an ovine PPD mRNA was subcloned by reverse transcription-polymerase chain reaction from sheep hypothalamus and used to create a (35)S-labeled riboprobe for in situ hybridization. Neurons that expressed PPD mRNA and DYN A immunoreactivity were widely distributed in the ovine preoptic area and hypothalamus. PPD mRNA-expressing cells were seen in the supraoptic nucleus, paraventricular nucleus, preoptic area, anterior hypothalamus area, bed nucleus of the stria terminalis, ventromedial nucleus (VMN), dorsomedial nucleus of the hypothalamus, and the arcuate nucleus. All of these regions also contained DYN A-positive cell bodies except for the VMN, raising the possibility that PPD is preferentially processed into other peptide products in the VMN. In summary, based on the expression of both mRNA and peptide, DYN cells are located in a number of key hypothalamic regions involved in the neuroendocrine control of homeostasis in sheep.

Primary structure of guinea pig preprodynorphin and preproenkephalin mRNAs: multiple transcription initiation sites for preprodynorphin

Preprodynorphin and preproenkephalin are protein precursors from which are derived two classes of opioid neurotransmitter peptides. Dynorphin A((1-17)) is produced by proteolytic processing of prodynorphin, and processing of proenkephalin yields the enkephalin peptides. We report here on the isolation and sequencing of multiple clones for these two mRNAs from a cDNA library. Two cDNA clones of preprodynorphin contained the full-length sequence (2.35 kb) with the primary structure predicted from the guinea pig gene sequence. In contrast, one clone encoded the full-length sequence but also an additional 192 nt at the 5' end. This sequence has high homology to the 5' flanking region of the human preprodynorphin gene, and RNase protection assays demonstrated that in addition to a primary initiation site, transcription of this mRNA is initiated at several sites 160-190 nt 5' with respect to the primary site. This difference may alter translational efficiency or mRNA stability. The sequence of preproenkephalin cDNA clones confirmed the structure predicted from the gene sequence. One clone, however, contained sequences encoded by exons 2 and 3, and initiated within the first intron (intron A) of the gene. We used RNase protection mapping to assess the abundance in the brain and pituitary of preproenkephalin transcripts that initiate within intron A. These studies confirmed that the primary transcription start site is 28 nucleotides downstream from the TATAA site, and that intron A sequences are not present in significant amounts in these tissues.

Analyzing the evolution of the opioid/orphanin gene family

Advances in molecular biology have made it possible to rapidly obtain the amino acid sequence of neuropeptide precursors-either by cloning and sequencing the cDNA that encodes the precursor, or by reconstructing the arrangement of exons and introns in a neuropeptide-coding gene through genomic approaches. The databases generated from these molecular approaches have been used to design probes to identify the cells that express the gene, or to ascertain the rate of expression of the gene, and even to predict the post-translational modifications that can generate functional neuropeptides from a biologically inert precursor. Although the power of these approaches is substantial, it is appreciated that a gene sequence or an mRNA sequence reflects the potential products that may be assembled in a secretory cell. To understand the functional capabilities of the secretory cell, the molecular genetics approaches must be combined with procedures that actually characterize the end-products generated by the secretory cell. Recent advances in two-dimensional gel electrophoresis and mass spectrometry now make it possible to analyze neuropeptides from a relatively small amount of tissue. These procedures can reveal novel end-products, tissue-specific endoproteolytic cleavage events, and developmental shifts in post-translational processing schemes. A gene family that illustrates all of these processes and the advantages of combining genomics with proteomics is the opioid/orphanin gene family.

Molecular evolution of the opioid/orphanin gene family

Gene duplication is a recurring theme in the evolution of vertebrate polypeptide hormones and neuropeptides. These duplication events can lead to the formation of gene families in which divergence of function is the usual outcome. In the case of the opioid/orphanin family of genes, duplication events have proceeded along two paths: (a) an apparent duplication of function as seen in the analgesic activity of Proenkephalin and Prodynorphin end-products; and (b) divergence of function as seen in the nociceptic activity of Proorphanin end-products or the melanocortin (color change and chronic stress regulation) activity of Proopiomelanocortin end-products. Although genes coding for Proopiomelanocortin, Proenkephalin, Prodynorphin, and Proorphanin have been extensively studied in mammals, the distribution and radiation of these genes in nonmammalian vertebrates is less well understood. This review will present the hypothesis that the radiation of the opioid/orphanin gene family is the result of the duplication and divergence of the Proenkephalin gene during the radiation of the chordates. To evaluate the Proenkephalin gene duplication hypothesis, a 3'RACE procedure was used to screen for the presence of Prodynorphin-related, Proenkephalin-related, and Proorphanin-related cDNAs expressed in the brains of nonmammalian vertebrates.

Interaction between anterior pituitary prodynorphin and the secretion of luteinizing hormone (LH)

The purpose of present research was to investigate the possible involvement of prodynorphin (proDYN)-derived peptides acting locally within the anterior pituitary (AP) on the effects of estradiol-17 beta (E2) and gonadotropin-releasing hormone (GnRH) on the release of luteinizing hormone (LH). Exposure of bovine AP cells in primary suspension cultures to E2 increased (P < 0.05) the spontaneous release of proDYN-derived peptides and also augmented (P < 0.05) the GnRH-induced release of LH. Both of these E2-induced responses required either high E2 dosages or prolonged exposure to produce significant changes, but there were a few cases in which the association between E2-induced changes in both parameters was absent. Therefore, it seems unlikely that proDYN-derived AP peptides mediate the effects of E2 on GnRH-induced LH release. Using another approach, cultured cells were exposed for 48 h to an antisense oligodeoxynucleotide (oligo) targeted against the translation initiation site of bovine proDYN. Compared with the two control treatments (scrambled oligo sequence or no oligo treatment), the antisense treatment decreased (P < 0.05) the quantity of LH released in response to challenge of the cells with 5 nM GnRH. There were no concurrent changes in cellular contents of proDYN-derived peptides or mRNA for LH-beta, but the antisense treatment tended to decrease (P < 0.10) the relative abundance of proDYN mRNA. In summary, proDYN-derived peptides probably do not mediate direct intrapituitary effects of E2 on LH, but the antisense treatment interfered in an unknown way with GnRH-induced release of LH from cultured AP cells.