The turkey transcription factor Pit-1/GHF-1 can activate the turkey prolactin and growth hormone gene promoters in vitro but is not detectable in lactotrophs in vivo

Seasonal differences in the transcriptome profile of the Zhedong white goose (Anser cygnoides) pituitary gland

In animals, the adaptation to breed at the time of greatest survival of the young is known as seasonal reproduction. This is mainly controlled by the photoperiod, which stimulates the hypothalamic-pituitary-gonadal axis and starts the breeding season. Herein, we have determined the seasonal changes in gene expression patterns of Zhedong white geese pituitary glands under a natural photoperiodism, conducted at autumn equinox (AE), winter solstice (WS), spring equinox (SE), and summer solstice (SS). Pairwise comparisons of WS vs. AE, SE vs. WS, SS vs. SE, and AE vs. SS resulted in 1,139, 33, 704, and 3,503 differently expressed genes, respectively. When compared with SS, AE showed downregulation of genes, such as vasoactive intestinal peptide receptor, prolactin receptor, and thyroid hormone receptor beta, whereas gonadotropin-releasing hormone II receptor was upregulated, indicating that these genes may be responsible for the transition from cessation to egg laying. In addition, the expression levels of 5 transcription factors (POU1F1, Pitx2, NR5A1, NR4A2, and SREBF2) and 6 circadian clock-associated genes (Clock, Per2, ARNTL2, Eya3, Dio2, and NPAS2) also changed seasonally. Gene Ontology term and Kyoto Encyclopedia of Genes and Genomes enrichment analysis revealed that “response to oxidative stress” and steroid biosynthesis pathway also participate in regulating the reproduction seasonality of geese. Overall, these results contribute to the identification of genes involved in seasonal reproduction, enabling a better understanding of the molecular mechanism underlying seasonal reproduction of geese.

Insights into the evolution of Darwin's finches from comparative analysis of the Geospiza magnirostris genome sequence

Background

A classical example of repeated speciation coupled with ecological diversification is the evolution of 14 closely related species of Darwin’s (Galápagos) finches (Thraupidae, Passeriformes). Their adaptive radiation in the Galápagos archipelago took place in the last 2–3 million years and some of the molecular mechanisms that led to their diversification are now being elucidated. Here we report evolutionary analyses of genome of the large ground finch, Geospiza magnirostris.

Results

13,291 protein-coding genes were predicted from a 991.0 Mb G. magnirostris genome assembly. We then defined gene orthology relationships and constructed whole genome alignments between the G. magnirostris and other vertebrate genomes. We estimate that 15% of genomic sequence is functionally constrained between G. magnirostris and zebra finch. Genic evolutionary rate comparisons indicate that similar selective pressures acted along the G. magnirostris and zebra finch lineages suggesting that historical effective population size values have been similar in both lineages. 21 otherwise highly conserved genes were identified that each show evidence for positive selection on amino acid changes in the Darwin's finch lineage. Two of these genes (Igf2r and Pou1f1) have been implicated in beak morphology changes in Darwin’s finches. Five of 47 genes showing evidence of positive selection in early passerine evolution have cilia related functions, and may be examples of adaptively evolving reproductive proteins.

Conclusions

These results provide insights into past evolutionary processes that have shaped G. magnirostris genes and its genome, and provide the necessary foundation upon which to build population genomics resources that will shed light on more contemporaneous adaptive and non-adaptive processes that have contributed to the evolution of the Darwin’s finches.

Role of chicken Pit-1 isoforms in activating growth hormone gene

In the present study, we expressed chicken (ch) Pit-1α (chPit-1α) and chPit-1γin vitro to compare the roles of chPit-1s in the transcription of the chicken growth hormone (chGH) gene. Both green fluorescence protein (GFP)-fused chPit-1γ and GFP-fused chPit-1α were localized in the nuclei of COS-7 cells. In a luciferase reporter gene assay, both chPit-1α and chPit-1γ transactivated the chGH promoter, and chPit-1α showed a more potent effect than chPit-1γ. On the other hand, an increase of cellular cAMP induced by forskolin promoted transactivation of the chGH gene with chPit-1α and chPit-1γ to similar extents. These results suggest that chPit-1γ may modulate the basal promoter activity of the chGH gene to the same degree as chPit-1α; however, a structural difference observed at the N-terminus transactivation domains in chPit-1α and chPit-1γ could be associated with the efficiency of basal activation of the chGH promoter.

Molecular cloning and characterisation of the Magang goose prolactin gene

In studying the roles of prolactin in regulation of seasonal reproduction, incubation, broodiness and laying performance in goose, the goose PRL gene was cloned in Magang goose. The goose PRL cDNA shared 98.4%, 92.2%, 92%, and 91.9% sequence homology to duck, turkey, chicken and quail PRLs, respectively. The goose PRL gene consisted of 5 exons and 4 introns, just as in other species. The 5' proximal regulatory region shared high homology with those in other avian species as well, and, apart from other non-specific transcription factor binding sites, contained 2 regulatory element binding sites, a Pit-1 (-130/-122) and a VIP response element (-64/-53). The deduced 199-residue mature goose PRL shared 98.5%, 94%, 93%, and 92% homology to duck, quail, chicken, and turkey PRLs, respectively. When compared with other vertebrates, all residues were found to be highly conserved at the key positions in the 4 conserved domains (PD1-PD4), including the 6 cysteine residues at positions 4, 11, 58, 175, 191, and 199. The only exception was a substitution of Arginine by Histidine at position 176 in the mature PRL peptide. These findings render goose PRL as having a similar hydropathy profile and similar secondary and tertiary structures with other PRLs. Goose PRL also possesses an N-linked glycosylation site (Asn-X-Ser), at position 6, and an alternative glycosylation site (Asn-Gly-Cys), at position 56. Five PRL isoforms were detected in goose, as well as in chicken pituitary glands, by immunoblotting analysis. Results of this study not only provided a starting point for further study of PRL function, synthesis, and secretion in goose species, but also for breeding new goose lines efficiently using the genomic information.

Polymorphisms of 5' flanking region of chicken prolactin gene

The polymorphisms of 5' flanking region of chicken prolactin (cPRL) gene were examined in several populations of Chinese native Yuehuang, Taihe Silkie and imported White Leghorn Layer chickens. The 5' flanking regions (2638 bp) from Yuehuang, Taihe Silkie and White Leghorn chickens were subjected to sequencing analysis. Four single nucleotide polymorphisms (SNPs) were identified at position -2425(C/T), -2215(T/C), -2063(G/A) and -1967(A/G). A 24-bp indel (insertion or deletion) and a polyA length polymorphism were also identified. For the 24-bp indel locus, three genotypes (AA, AB and BB) were found in Yuehuang chickens, while only two genotypes were detected in Taihe Silkie (AB and BB) and Leghorn chickens (AA and BB). The genotype frequencies of AA, AB and BB were significantly different among the three breeds. For the polyA locus, although three genotypes (CC, CD and DD) were found, only one genotype (CC) was detected in White Leghorn chickens, while two or three genotypes were observed in Chinese native chickens. We used real-time quantitative PCR and radioimmunology assay to investigate the potential association of the 24-bp indel locus with cPRL mRNA expression, plasma cPRL and brooding behaviors, and observed that chickens with genotype AB, which are of the highest incidence of broodiness, had the highest cPRL mRNA levels, providing the possibility that this polymorphic site might be related to the broodiness in chickens via modulating the transcriptional level of cPRL gene. The dissociation among cPRL gene transcription, mRNA storage and hormone release was also observed.

Regulation of pituitary somatotroph differentiation by hormones of peripheral endocrine glands

Anterior pituitary somatotroph differentiation occurs during chick embryonic and rat fetal development. A number of findings support the hypothesis that differentiation of these growth hormone (GH) producing cells in the chick and the rat is regulated by adrenal glucocorticoids and thyroid hormones. Somatotroph differentiation can be induced in cultures of chick embryonic and rat fetal pituitary cells with adrenal glucocorticoids and this effect can be modulated by concomitant treatment with thyroid hormones. Plasma levels of thyroid hormones, corticosterone and adrenocorticotropic hormone increase during development, consistent with the ontogeny of somatotrophs. Treatment of chick embryos or rat fetuses with glucocorticoids in vivo induces premature somatotroph differentiation, indicating that the adrenal gland, and ultimately anterior pituitary corticotrophs, may function to regulate pituitary GH cell differentiation during development. Administration of thyroid hormones in vivo also increases somatotrophs prematurely, and administration of the thyroid hormone synthesis inhibitor methimazole inhibits somatotroph differentiation in vivo, suggesting that endogenous thyroid hormone synthesis contributes to normal somatotroph differentiation. Our working model for the regulation of somatotroph differentiation during normal development includes modulation by elements of the hypothalamo-pituitary-adrenal and hypothalamo-pituitary-thyroid axes. Additional research is reviewed defining the mechanism of action for these peripheral hormones in induction of pituitary GH gene expression during development.

Cloning of duck PRL cDNA and genomic DNA

Complementary DNA (cDNA) and genomic DNA, including flanking regions of the prolactin (PRL) gene of domesticated duck, were cloned and sequenced. Duck PRL was found to have 92.0, 91.7, and 91.4% sequence identity at the cDNA level to PRL of chicken, turkey, and quail, respectively. The predicted amino acid sequence had an overall similarity with a comparable region of chicken (93.4%), turkey (91.3%), and quail (91.3%) PRL. Mature duck PRL contains the consensus sequence for N-linked glycoslylation at position 6 which is not present in either chickens or turkeys. Thus, duck PRL is likely to be post-translationally modified differently from other avian species. Based on the cDNA sequence, the genomic structure of the gene was characterized. The duck PRL gene consists of 5 exons and 4 introns. Moreover, sequence analysis of the proximal region of duck PRL promoter revealed a high degree of similarity to that of chicken and turkey PRL promoter. These results suggest that the mechanisms, which regulate expression of the PRL gene, may be widely conserved in avian species.

A new single nucleotide polymorphism in the chicken pituitary-specific transcription factor (POU1F1) gene associated with growth rate

The pituitary-specific transcription factor (POU1F1) is a protein which binds to and transactivates promoters of growth hormone (GH), prolactin (PRL) and thyroid-stimulating hormone chain (TSHB)-encoding genes. Ten chicken populations (n = 662), including six Chinese indigenous breeds, White Leghorn, paternal/maternal lines of brown egg layer and a paternal line of broiler, were used to detect single nucleotide polymorphisms in the pituitary-specific transcription factor gene (PIT1) by means of PCR-SSCP. A nucleotide transversion from adenine (A) to thymidine (T) at position 980 of the open reading frame of the PIT1 cDNA (GenBank accession no. AF029892) was identified. This nucleotide transversion results in an alteration of codon 299 from AAC to ATC, which leads to a change from asparagine (Asn) to isoleucine (Ile) in the POU domain of POU1F1. The distribution of allele and genotype frequencies differed significantly between meat-type chickens (higher frequencies of A and A/A) and layer-type chickens (P < 0.01). Another experimental population with growth records was used to evaluate the relationship between this polymorphism and growth rate. The results revealed a positive relationship between genotype A/A and body weight at 8 weeks of age, indicating that the SNP in PIT1 gene is a potential molecular marker for early growth rate in chicken.

Turkey prolactin gene regulation by VIP through 35-bp cis-acting element in the proximal promoter

Vasoactive intestinal peptide (VIP) has been shown to increase prolactin (PRL) gene expression and secretion in turkey primary anterior pituitary cells. To characterize cis-acting elements involved in stimulation of PRL gene expression by VIP, 5'-flanking deletions and/or mutations of the turkey PRL promoter fused to the luciferase (Luc) reporter gene have been constructed for use in transient transfection assays. Deletion analysis of the turkey PRL promoter (tPRLP) indicated that the VIP-stimulated tPRLP activity was controlled by three major positive regulatory regions and two negative regions. The -74/+40 Luc construct exhibited a 7- to 8-fold increase in promoter activity in response to VIP treatment. Deletion of the 35-bp segment (-74/-40) or fusion of this sequence to the SV40 promoter demonstrated that a VIP response element (VRE) was present in this region. Functional analysis of this VRE (-74/-40) was performed by mutation of core sequences (TGAATGTATGCA, -61/-50) or deletion of a 35-bp segment and a Decoy assay. Electrophoretic mobility shift assays revealed the presence of three DNA-protein complexes bound to the region -73 to -41. The results of the present study demonstrated that VRE (35-bp) in the proximal PRL promoter is an important cis-acting element for VIP-stimulated PRL gene expression in turkey primary anterior pituitary cells.

Characterization of the 5'-flanking transcriptional regulatory region of chicken growth hormone gene

A 1727-bp fragment of 5'-flanking region of chicken growth hormone (cGH) gene has been cloned and sequenced. Various lengths of the 5'-flanking region (122 to 1775 bp) was linked to a luciferase reporter gene, and its transcriptional regulation was examined by an in vitro transient transfection coupled with luciferase assay. Our results demonstrated that pituitary-specific transcription factor, Pit-1, is necessary and sufficient to confer a strong tissue-specific expression. Co-transfection with goldfish or chicken Pit-1 expression vectors significantly restored the luciferase expression in HeLa cells. Site-directed mutagenesis and mobility gel-shift assays further confirmed the position of the Pit-1 binding site at -113/-104. Moreover, a repressive thyroid hormone response element (TRE) was identified at -137/-74, and we propose that interactions between the TRE and Pit-1 sites may be required for its repressive effect.