Primary Structure of Chicken Pituitary Prolactin Deduced from the cDNA Sequence

Polymorphisms of the prolactin gene and their association with egg production traits in two Chinese domestic ducks

1. Prolactin (PRL) as a polypeptide hormone which plays a crucial role in egg production traits. 2. Polymorphisms of the PRL gene were analysed with DNA sequencing and polymerase chain reaction-single-strand conformation polymorphism methods in two Chinese domestic laying duck breeds (Jinding, n = 400, Youxian, n = 400, respectively). 3. The results showed that one polymorphism was detected (A-412G) in intron 1 of the PRL gene, with three genotypes: AA, AG and GG. Association analysis showed that the ducks with the GG genotype had significantly greater egg production and egg weight than those with AG and AA genotype (p < 0.05). Hence, the 412A > G polymorphism of the PRL gene in intron 1 is a potentially valuable genetic marker for laying duck breeding programmes.

Neuroendocrine Control of Broodiness

In the majority of vertebrates, survival of offspring to sexual maturation is important for increasing population size, and parental investment in the young is important for reproductive success. Consequently, parental care is critical for the survival of offspring in many species, and many vertebrates have adapted this behavior to their social and ecological environments. Parental care is defined as any behavior that is performed in association with one's offspring (Rosenblatt, Mayer, Siegel. Maternal behavior among nonprimate mammals. In: Adler, Pfaff, Goy, editors. Handbook of behavioral neurobiology. New York: Plenum; 1985. p. 229-98) and is well characterized in mammals and birds. In birds (class Aves), this is due to the high level of diversity across species. Parental behavior in birds protects the young from intruders, and generally involves nest building, incubation, and broody behavior which protect their young from an intruder, and the offspring are reared to independence. Broodiness is complexly regulated by the central nervous system and is associated with multiple hormones and neurotransmitters produced by the hypothalamus and pituitary gland. The mechanism of this behavior has been extensively characterized in domestic chicken (Gallus domesticus), turkey (Meleagris gallopavo), and pigeons and doves (family Columbidae). This chapter summarizes broodiness in birds from a physiology, genetics, and molecular biology perspective.

Comparison of in vitro bioactivity of chicken prolactin and mammalian lactogenic hormones

Recombinant chicken prolactin, expressed in Escherichia coli as an unfolded protein, was successfully refolded and purified to homogeneity as a monomeric protein. Its biological activity was evidenced by its ability to interact with rabbit prolactin receptor extracellular domain and stimulate prolactin receptor-mediated proliferation in three cell types possessing mammalian prolactin receptors. Chicken prolactin activity in those assays was 20-100-fold lower than that of mammalian lactogenic hormones, likely due to lower affinity for mammalian prolactin receptors and not to improper refolding, because in two homologous bioassays, chicken prolactin activity was equal to or higher than that of ovine prolactin and the CD spectra of chicken and human prolactin were almost identical. Our results using seven mammalian lactogenic hormones from five species in three bioassays revealed the major role of species specificity in testing biological activity in vitro. Heterologous bioassays may be misleading and homologous assays are strongly recommended for predicting the activity of species-specific lactogenic hormones in vivo.

Extra-pituitary prolactin (PRL) and prolactin-like protein (PRL-L) in chickens and zebrafish

It is generally believed that in vertebrates, prolactin (PRL) is predominantly synthesized and released by pituitary lactotrophs and plays important roles in many physiological processes via activation of PRL receptor (PRLR), including water and electrolyte balance, reproduction, growth and development, metabolism, immuno-modulation, and behavior. However, there is increasing evidence showing that PRL and the newly identified 'prolactin-like protein (PRL-L)', a novel ligand of PRL receptor, are also expressed in a variety of extra-pituitary tissues, such as the brain, skin, ovary, and testes in non-mammalian vertebrates. In this brief review, we summarize the recent research progress on the structure, biological activities, and extra-pituitary expression of PRL and PRL-L in chickens (Gallus gallus) and zebrafish (Danio rerio) from our and other laboratories and briefly discuss their potential paracrine/autocrine roles in non-mammalian vertebrates, which may promote us to rethink the broad spectrum of PRL actions previously attributed to pituitary PRL only.

Cloning of PRL and VIP cDNAs of the Java sparrow (Padda oryzivora)

Complementary DNA (cDNA) of prolactin (PRL) and vasoactive intestinal polypeptide (VIP) of the Java sparrow were cloned and sequenced. The proximal region of the PRL promoter was also identified. Java sparrow PRL was found to have 88.3, 88.3, and 89.1% sequence identity at the cDNA level to PRL of chicken, turkey, and duck, respectively. The predicted amino acid sequence had an overall similarity with a comparable region of chicken (91.4%), turkey (88.9%) and duck (92.0%) PRL. Based on the cDNA sequence and genomic structure of the chicken PRL gene, the proximal promoter was characterized. Sequence analysis of the proximal region of Java sparrow PRL promoter revealed a high degree of similarity to that of chicken, turkey and duck PRL promoters. Moreover, cDNA of prepro-VIP was also cloned and sequenced. Java sparrow prepro-VIP shows high similarity to chicken and turkey prepro-VIP. However, the region upstream of the 5' untranslated region of Java sparrow prepro-VIP did not show similarity to that of chicken. These results suggest that the mechanisms, which regulate expression of the VIP gene, may be different between precocial and altricial birds, but expression of the PRL gene may be widely conserved in avian species.

Prolactin-dependent modulation of organogenesis in the vertebrate: Recent discoveries in zebrafish

The scientific literature is replete with evidence of the multifarious functions of the prolactin (PRL)/growth hormone (GH) superfamily in adult vertebrates. However, little information is available on the roles of PRL and related hormones prior to the adult stage of development. A limited number of studies suggest that GH functions to stimulate glucose transport and protein synthesis in mouse blastocytes and may be involved during mammalian embryogenesis. In contrast, the evidence for a role of PRL during vertebrate embryogenesis is limited and controversial. Genes encoding GH/PRL hormones and their respective receptors are actively transcribed and translated in various animal models at different time points, particularly during tissue remodeling. We have addressed the potential function of GH/PRL hormones during embryonic development in zebrafish by the temporary inhibition of in vivo PRL translation. This treatment caused multiple morphological defects consistent with a role of PRL in embryonic-stage organogenesis. The affected organs and tissues are known targets of PRL activity in fish and homologous structures in mammalian species. Traditionally, the GH/PRL hormones are viewed as classical endocrine hormones, mediating functions through the circulatory system. More recent evidence points to cytokine-like actions of these hormones through either an autocrine or a paracrine mechanism. In some situations they could mimic actions of developmentally regulated genes as suggested by experiments in multiple organisms. In this review, we present similarities and disparities between zebrafish and mammalian models in relation to PRL and PRLR activity. We conclude that the zebrafish could serve as a suitable alternative to the rodent model to study PRL functions in development, especially in relation to organogenesis.

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.

Independent differentiation of mammotropes and somatotropes in the chicken embryonic pituitary gland. Analysis by cell distribution and attempt to detect somatomammotropes

It has been reported that mammotropes in a rodent pituitary gland are derived from somatotropes via somatomammotropes (SMTs), cells that produce both growth hormone (GH) and prolactin (Prl). However, no studies have been done on the transdifferentiation of somatotropes in the chicken pituitary gland. In this study, in order to determine the origin of mammotropes, we studied detail property of appearance of chicken somatotropes, mammotropes and pit-1 cells and then evaluated the existence of SMTs in the chicken embryonic pituitary gland. Immunohistochemical analysis revealed that GH-immunopositive (GH-ip) cells appeared on embryonic day (E) 14 and were mainly distributed in the caudal lobe, while Prl-immunopositive (Prl-ip) cells appeared in the cephalic lobe of the pituitary gland on E16. In situ hybridization (ISH) and RT-PCR analysis showed that expression of GH and Prl mRNA starts at E12 in the caudal lobe and at E14 in the cephalic lobe respectively. Pit-1 mRNA was first detected on E5 by RT-PCR, and pit-1 mRNA-expressing cells were found in the cephalic lobe on E8. Then with the ontogeny of the chicken, these cells spread into both lobes. Using a double staining method with ISH and immunohistochemistry, we could not detect the existence of SMTs in the chicken embryonic pituitary gland even in the marginal region of either lobe. These results suggest that chicken somatotropes and mammotropes independently appear in different lobes of pituitary gland and that transdifferentiation from somatotropes to mammotropes is not the central route for differentiation of mammotropes in the embryonic chicken pituitary gland.

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.

Cloning and expression of a new member of prolactin-related protein in bovine placenta: bovine prolactin-related protein-VII

This study reports the identification and sequence of a full-length cDNA for a new member of bovine prolactin-related protein (bPRP-VII) and its quantitative and localized expression in the placenta. A full-length bPRP-VII cDNA was cloned with a 929-nucleotide open-reading-frame corresponding to a protein of 238 amino acids. The predicted amino acid sequence shares 63% homology with bPRP-I and 70% with bPRP-VI. bPRP-VII has eight cysteine residues with four disulfide bonds, which is more abundant than that of other bPRPs. RT-PCR detected bPRP-VII only in the placenta. In the placenta, mRNA was expressed in the cotyledon and intercotyledonary tissues throughout gestation. Quantitative real-time RT-PCR analysis exhibited a high expression of bPRP-VII mRNA in the fetal membrane at Day 27 of gestation. In the placentome on Day 60 of gestation, in situ hybridization analysis evidenced bPRP-VII mRNA in binucleate cells. bPRP-VII gene produced a mature protein in mammalian cell expression system. Approximately 29kDa protein was confirmed in this by the Western blot analysis with FLAG epitope tag. Expression profiles and localization were similar to those of bPRP-I. Although the functional data remain to be examined, a new member of the bPRP-VII gene was cloned. In addition to bPRP-I, bPRP-VII may take on an important functional role in implantation.

Molecular cloning of newt prolactin (PRL) cDNA: effect of temperature on PRL mRNA expression

A partial prolactin (PRL) cDNA was specifically PCR amplified from a cDNA library constructed from pituitary mRNAs of the newt (Cynops pyrrhogaster) and cloned into plasmid vectors. One clone thus obtained contained a 739-bp insert encoding the C-terminal amino acid sequence of the mature hormone molecule. Using this clone as a probe, the full-length newt PRL cDNA was screened from the cDNA library. The PRL cDNA clone thus obtained consisted of 1024 bp encoding the entire sequence of the mature PRL molecule in addition to its signal peptide. The amino acid sequence of newt PRL deduced from its nucleotide sequence showed higher homologies with those PRL sequences of tetrapod animals than with those of teleosts. Northern blot analysis revealed the newt PRL mRNA size to be approximately 1 kb. In situ hybridization using the newt PRL cDNA as a probe revealed that the pituitary region expressing PRL mRNA corresponded to that immunoreactive with antiserum against PRL. PRL mRNA levels in the pituitary of newts subjected to room and low temperatures were determined by Northern analysis employing the PRL cDNA as a probe. PRL mRNA levels were significantly higher in the pituitaries of newts subjected to 10 degrees than in those of newts kept at 23 degrees. Likewise, immunoassayable plasma PRL levels were higher in animals subjected to 10 degrees than in those kept at 23 degrees.

Newt prolactin and its involvement in reproduction

The amino acid sequence of newt (Cynops pyrrhogaster) prolactin deduced from the nucleotide sequence of its cDNA showed a relatively high homology with sequences of chicken and sea turtle prolactins as well as with those of anuran prolactins. Cynops prolactin receptor transcripts were detected in various tissues and organs, suggesting that prolactin plays multiple roles in urodeles. Urodele prolactin was purified from the pituitaries of C. pyrrhogaster. Antiserum against this prolactin was used for radioimmunoassay of plasma prolactin and immunoneutralization experiments. Endogenous prolactin was shown to induce migration to water, courtship behavior, and cessation of spermatocytogenesis in the Cynops newt. The hormone was found to be involved in the development of cloacal glands such as the lateral and abdominal glands, growth of the tail and Mauthner neurons, secretion of oviducal jelly, and enhanced synthesis of a female attracting pheromone (sodefrin), and responsiveness of the olfactory epithelium to sodefrin. In most of these cases, prolactin was found to act synergistically or antagonistically with sex steroids. We also discovered that hypersecretion of prolactin in the newts subjected to cold temperature was induced by hypothalamic stimulation rather than release from hypothalamic inhibition.Key words: prolactin, newts, reproduction.

Molecular cloning of the chicken prolactin gene and activation by Pit-1 and cAMP-induced factor in GH3 cells

Transcription of the prolactin (PRL) gene has been reported to be activated by a nuclear factor, Pit-1. However, the precise molecular mechanisms of the Pit-1-mediated PRL gene activation are still unclear. We have cloned the chicken PRL (cPRL) gene and its 5'-flanking region to analyze their structure and transcription-initiating mechanism. In luciferase assay, forskolin activated the proximal promoter region between -248 and -76 to transcribe the cPRL gene in GH3 cells, although there is no canonical cyclic AMP-responsive element in the promoter region. In gel mobility shift assay, a DNA fragment between -104 and -76 containing a putative Pit-1 binding site was bound by nuclear factors from the GH3 cells. Furthermore, it was observed that Pit-1 protein specifically bound to the DNA fragment in the supershift assay. These results indicate that both Pit-1 and cAMP-induced factor(s) associated with the cis element on the proximal promoter region to activate cPRL gene expression in GH3 cells.

cDNA cloning and developmental alterations in gene expression of the two Pit-1/GHF-1 transcription factors in the chicken pituitary

Pit-1/GHF-1 (Pit-1) transcription factors promote the gene expressions for growth hormone (GH), prolactin (PRL), and the beta chain of thyroid-stimulating hormone in vertebrate pituitary glands. The present study analyzed the nature of chicken Pit-1s (cPit-1s) and their developmental expressions in the pituitary. Chicken pituitary expressed two cPit-1 mRNAs encoding cPit-1alpha and cPit-1gamma composed of 335 and 327 amino acid residues, respectively. They possessed different N-terminal regions and the common C-terminal regions containing a POU-specific domain and a POU homeodomain. Northern blot analysis revealed the pituitary-specific expressions of these Pit-1 mRNAs, and the Pit-1alpha mRNA expressions were two to three times higher than those for Pit-1gamma in both cephalic and caudal lobes of the pituitary. The cPit-1alpha and gamma mRNA expressions simultaneously increased after hatching until 4 weeks and then slightly decreased at 5 weeks. Similar gene expression profiles were observed for GH and PRL during the posthatch developmental period.

The prolactin gene is expressed in the mouse kidney

BACKGROUND

Prolactin (PRL), originally identified as an anterior pituitary hormone exhibiting lactogenic activity, is now recognized as a versatile hormone expressed in a wide variety of tissues.

METHODS

In this study, the expression of PRL in the mouse kidney was investigated by solution-phase and in situ reverse transcription-polymerase chain reaction (RT-PCR) methods and immunohistochemistry.

RESULTS

Mouse PRL (mPRL) transcript and protein are localized in the parietal epithelial cells of Bowman's capsule. Pit-1 is a positive transcription factor for the expression of the PRL gene. The presence of Pit-1 transcript in the kidney was also assessed by RT-PCR methods. The localization of Pit-1 mRNA coincided well with that of PRL. Immunoreactivity to mouse PRL receptor (mPRL-R) is distributed on the luminal membrane of the proximal tubule cells and the parietal epithelial cells of Bowman's capsule.

CONCLUSION

These data indicate that the parietal epithelial cells of Bowman's capsule synthesize PRL de novo and suggest that Pit-1 contributes to the transcriptional regulation of PRL gene expression in the kidney, and PRL expressed in this tissue functions in an autocrine/paracrine fashion.

Prolactin receptor gene expression in the brain and peripheral tissues in broody and nonbroody breeds of domestic hen

The objective of this study was to establish whether the gene encoding prolactin receptor (PRLR) is expressed in the hypothalamus and peripheral tissues of the domestic chicken and, if so, to determine whether there are breed differences in the structure or expression of the gene which might account for the observation that broodiness does not occur in the White Leghorn hen but does occur in other breeds of domestic hens, including the bantam. A preliminary experiment demonstrated that the absence of broodiness in White Leghorns is not due to a lack of a prolactin response to the avian prolactin-releasing hormone vasoactive intestinal polypeptide. The largest amounts of PRLR mRNA in the brain, which did not differ significantly between laying White Leghorns and bantams, were found in the pituitary gland and basal and preoptic hypothalamus. Small or nondetectable amounts were found in both breeds in the forebrain, cerebellum, and optic lobes. Prolactin receptor mRNA was widely distributed in peripheral tissues in both breeds, in the following descending order of abundance: kidney, leg skin, brood patch, duodenum, intestine > thyroid gland > adrenal gland, liver, ovary >> adipose tissue > thymus, spleen > muscle > blood. Southern blotting analysis using four restriction enzymes and a chicken PRLR cDNA probe demonstrated identical digestion patterns for White Leghorn and bantam genomic DNA. Northern blotting analysis identified two sizes of chicken PRLR mRNA transcripts (7.5 and 3.3 kb) in hypothalami from laying White Leghorn and bantam hens. It is concluded that differences in the expression of broodiness in White Leghorn and bantam hens cannot be explained by differences in the amounts of PRLR mRNA in the hypothalamus or in the transcription or gross structure of the PRLR gene.

Lungfish prolactin exhibits close tetrapod relationships

This paper describes the isolation and the complete amino-acid sequence of prolactin (PRL) from the pituitary glands of African lungfish, Protoputerus aethiopicus. We purified the hormone from an alkaline extract of the pituitaries using a two-step chromatographic procedure by detecting specific immunoblot reactivity with rabbit antisera against salmon PRL. The lungfish PRL consists of 200 amino-acid residues. Sequence comparison revealed that the PRL shows 66% identities with amphibian, reptilian and bird PRLs, 57% with mammalian PRLs, and 38% with teleost (modern bony fish) PRLs. Moreover, the PRL contains three disulfide bonds homologous to those of tetrapod PRLs and differs from teleost PRLs which lack the amino-terminal disulfide bond. Thus, the structural features of lungfish PRL indicate a closer relationship to tetrapod PRLs than to teleost PRLs. All PRLs sequenced to date share 22 common amino acids, which may be important for the activities common to all PRLs.

High-level expression of biologically active chicken prolactin in E. coli

1. A large quantity of chicken prolactin (cPRL) was produced by manipulating the cPRL cDNA clone and an expression vector pKK223-3. To augment the production of the hormonal protein in E. coli, in addition to the potent tac promoter, a unique DNA linker containing a pair of Shine-Dalgarno sequences and a short preceding cistron sequence was inserted into adjacent 5'-region of the coding region. 2. In sodium dodecyl sulfate polyacrylamide gel electrophoresis analysis, recombinant cPRL protein exhibited a molecular mass of 23 kDa. 3. The recombinant cPRL showed equivalent binding kinetics to an antiserum raised against turkey PRL. Also, this product increased the weight of pigeon crop sac mucosa to a degree comparable to that induced by turkey PRL. 4. These results indicate that this recombinant cPRL has immunological and biological activities identical to those of authentic avian PRL.

Immunocytochemistry and immunoblotting of avian prolactins using polyclonal and monoclonal antibodies toward a synthetic fragment of chicken prolactin

A major obstacle in the production of specific antibodies toward chicken prolactin (PRL) has been overcome by mimicking a putative epitope of the molecule using the synthetic decapeptide Lys-chPRL 59-67. This peptide represents the highest hydrophilicity peak of the amino acid sequence of chPRL that was recently derived from the nucleotide sequence. Polyclonal mouse antisera against the fragment specifically recognized the lactotropes in the cephalic lobe of the chicken pars distalis as illustrated by immunocytochemical double staining experiments. Monoclonal antibody production yielded antibodies that specifically labeled purified turkey PRL upon SDS-PAGE separation and immunoblotting. Turkey and chicken PRL showed a very similar polymorphism with respect to their apparent molecular weights, including the occurrence of a glycosylated variant of chicken PRL. The monoclonal antibodies were finally used to demonstrate the presence of PRL-like immunoreactivity both in the pituitary gland and in the brain of the quail. In the brain, immunoreactive neurons were in the nucleus accumbens and in the lateral parts of the ventro-medial hypothalamus, partly similar to those described in the rat.

Isolation and characterization of glycosylated and non-glycosylated prolactins from alligator and crocodile

Two molecular forms of prolactin (PRL), glycosylated and non-glycosylated, were isolated from pituitary glands of two reptiles, alligator and crocodile. The reptilian PRLs were extracted under alkaline conditions from the precipitate obtained after pituitaries were first extracted with 0.25 M sucrose, 1 mM NH4HCO3, pH 6.3. Purification was performed by ion exchange chromatography on DE-52, gel filtration on Sephadex G-75 superfine, and reversed phase high performance liquid chromatography. Two forms of both alligator and crocodile PRL, designated PRLI and PRLII, with molecular weights of 26,000 and 24,000 were isolated. Alligator and crocodile PRLI and PRLII were stained specifically in immunoblots with anti-sea turtle PRL and anti-ostrich PRL. Sequence analysis revealed that both forms of alligator and crocodile PRLs consisted of 199 amino acid residues with a glycosylation consensus sequence (Asn-Ala-Ser) at position 60 in alligator and crocodile PRLs with a molecular weight of 26,000 (PRLI). In contrast, Thr was substituted for Asn at position 60 in the PRLs with a molecular weight of 24,000 (PRLII). The sequences of alligator PRLs differed from crocodile PRLs only in position 134: Val for alligator PRLs and Ile for crocodile PRLs. There is a high degree of structural conservation between the reptilian PRLs isolated in this study and avian PRL; each showed 92% sequence identity with chicken PRL and 89% with turkey PRL.

Developmental expression of the prolactin gene in the chicken

Steady-state levels of prolactin (PRL) mRNA in the pituitary gland during embryonic development were determined by dot blot analyses to relate the changes with those of pituitary and plasma levels of PRL. Steady-state levels of the 1.38-kb mRNA encoding the PRL prohormone remained low until Day 18 of incubation, increased on Day 19 of incubation, and reached maximum levels on the day of hatch but decreased 1 day after hatch. Changes in both pituitary and plasma concentrations of PRL closely mimicked those changes in PRL mRNA levels. Subsequently, both the levels of the pituitary PRL mRNA and PRL remained unchanged whereas those of plasma PRL increased 7 days after hatch. The results indicate that a progressive expression of PRL gene in the pituitary gland occurs 1-2 days before the hatch and concomitant increases in plasma concentrations of prolactin may be associated with physiologic changes in pulmonary respiration and hatching.

The complete amino acid sequence of prolactin from the bullfrog, Rana catesbeiana

The complete amino acid sequence of prolactin (PRL) from an amphibian species, the bullfrog (Rana catesbeiana), has been determined and conserved residues and domains were analyzed by sequence comparison of PRLs from 15 species of five major vertebrate classes. The bullfrog PRL consists of 197 amino acid residues with three disulfide linkages formed between residues 4-11, 58-172, and 189-197. The bullfrog PRL shows the highest identity with sea turtle PRL (75%); lower identities with chicken PRL (72%), pig, horse, and fin whale PRLs (68%), human, cattle, sheep, and elephant PRLs (60-58%), and rat and mouse PRLs (50%); and significantly lower identity with teleost PRLs (about 30%). It is apparent that all tetrapod PRLs characterized so far contain three disulfide bonds in homologous positions and differ from teleost PRLs which lack the N-terminal disulfide loop. The tetrapod and teleost PRLs share 34 common residues and these conserved residues are clustered in six domains (PD1 to PD6), suggesting that these common residues, or at least part of them, are responsible for the activities common to all PRLs. On the other hand, PD5 is conserved significantly within tetrapod PRLs, but to a lesser extent in teleost PRLs, suggesting that the PD5 contributes to the activities specific to tetrapod PRLs.

The complete amino acid sequence of growth hormone of the bullfrog (Rana catesbeiana)

The primary structure of growth hormone (GH) isolated from the adenohypophysis of the bullfrogs (Rana catesbeiana) was determined. The hormone was reduced, carboxymethylated and subsequently cleaved with cyanogen bromide. Intact bullfrog GH was also digested with lysyl endopeptidase and trypsin. The resulting fragments were separated by reverse-phase high-performance liquid chromatography and subjected to sequence analysis using an automated gas-liquid sequencer employing the Edman method. Bullfrog GH was found to consist of 190 amino acid residues. The amino acid sequence determined is in accord with that deduced from bullfrog GH cDNA by Pan and Chang (1988) except for nine residues at positions 43-48, 73, 80 and 87. Sequence comparisons revealed that bullfrog GH is more similar to tetrapod GHs (e.g., 69% homology with sea turtle GH, 66% with chicken GH and 61% with ovine GH) than to GHs of teleosts (e.g., 35% homology with chum salmon GH and 33% with bonito GH) except for eel (52% identity). Bullfrog GH and prolactin exhibit a sequence homology of 25%.

Cloning of a turkey prolactin cDNA: expression of prolactin mRNA throughout the reproductive cycle of the domestic turkey (Meleagris gallopavo)

A cDNA-encoding turkey prolactin (PRL) has been isolated from a turkey pituitary library. The 953-base pair cDNA clone contains a 229-amino acid open reading frame which consists of a 30-amino acid signal peptide followed by a 199-amino acid mature PRL. The deduced amino acid sequence of turkey PRL shows greater than 90% homology to chicken PRL and 54-78% homology to other mammalian prolactins. A mRNA of 1100 nucleotides was detected in total RNA extracted from turkey pituitaries. Levels of PRL mRNA increased approximately 10-, 20-, and 100-fold in photostimulated, laying, and incubating hens, respectively, relative to that found in nonphotostimulated hens. The corresponding increases in plasma PRL levels were 2-, 5.5-, and 50-fold and in pituitary PRL content were 2-, 4-, and 13.4-fold, respectively. The transition from incubation to the photorefractory phase resulted in a 10-fold reduction in PRL mRNA, a 3.7-fold decrease in pituitary PRL, and a dramatic 50-fold decrease in plasma PRL. The changes in the abundance of pituitary PRL mRNA appear to be related to the changes in PRL-releasing activity observed at each of the reproductive stages. This study provides the first characterization of pituitary PRL mRNA and its comparison with plasma and pituitary PRL levels during the avian reproductive cycle.

Determination of the primary and secondary structures of the dromedary (Camelus dromedarius) prolactin and comparison with prolactins from other species

A non-glycosylated form of camel prolactin (camPRL), isolated from one-humped camel (Camelus dromedarius) pituitaries, was totally sequenced. A glycosylated form, separated by affinity chromatography on ConA-Sepharose, was partially sequenced. The comparison of the N-terminal amino acid sequences of the glycosylated and non-glycosylated forms showed that the only putative site of N-glycosylation (Asn-31) was indeed glycosylated. The far ultraviolet (UV) circular dichroism (CD) spectra of the two isohormones were identical, suggesting that the carbohydrate moiety had no effect on the global camPRL secondary structure. The far UV circular dichroism spectra of the two isohormones were analyzed in order to determine their relative proportions of periodic secondary structure, 60% of which was found to be in alpha-helix, as in prolactins of other species. The dromedary sequence was compared to those of other species and interpreted in term of evolutionary process. As already found for gonadotropins, the closest species to the dromedary was found to be the pig.

A novel cDNA clone encoding a prolactin-like protein that lacks the two C-terminal cysteine residues isolated from bovine placenta

A new prolactin-like cDNA clone, bPLP-IV, was isolated from a bovine placental cDNA library and the complete nucleotide sequence was determined. The bPLP-IV encodes a protein consisting of 237 amino acids, which is related to, but different from seven other known bovine prolactin-like proteins including two placental lactogens. The predicted amino acid sequence of the bPLP-IV shows over 52% identity to other known members of bovine prolactin-like proteins, 48% to bovine prolactin, 40% to both two bovine placental lactogens and only 22% to bovine growth hormone. The bPLP-IV protein has a unique feature in its primary structure, lacking the two C-terminal cysteine residues which are completely conserved in all other known members of prolactin-growth hormone-placental lactogen gene family. The expression of bPLP-IV in developing bovine placenta was apparently stage-specific, being maximal in the full-term placenta.

The complete amino acid sequence of prolactin from the sea turtle (Chelonia mydas)

The complete amino acid sequence of prolactin (PRL) from a reptile, the sea turtle (Chelonia mydas), was determined for the first time. Sequence analysis was performed on fragments obtained from cleavage of intact and performic acid-oxidized hormone with lysyl endopeptidase, Staphylococcus aureus protease, and o-iodosobenzoic acid employing manual Edman degradation. The sea turtle PRL consists of 198 amino acid residues with three disulfide linkages formed between residues 4-11, 58-173, and 190-198 and possesses heterogeneity indicated by four replacements at positions 55, 145, 148, and 171. Sequence comparison with other vertebrate PRLs revealed that the degree of sequence identity conforms well to expectations based on phylogeny except for the rodent PRLs; sea turtle PRL has 86% identity with chicken PRL; 81% with horse, pig, and fin whale PRLs; 75-71% with cattle, sheep, and human PRLs; 60-56% with mouse and rat PRLs; and 35-31% with carp, salmon, and tilapia PRLs.