cDNA cloning of eel (Anguilla anguilla) somatolactin

Evolution of the growth hormone, prolactin, prolactin 2 and somatolactin family

Growth hormone (GH), prolactin (PRL), prolactin 2 (PRL2) and somatolactin (SL) belong to the same hormone family and have a wide repertoire of effects including development, osmoregulation, metabolism and stimulation of growth. Both the hormone and the receptor family have been proposed to have expanded by gene duplications in early vertebrate evolution. A key question is how hormone-receptor preferences have arisen among the duplicates. The first step to address this is to determine the time window for these duplications. Specifically, we aimed to see if duplications resulted from the two basal vertebrate tetraploidizations (1R and 2R). GH family genes from a broad range of vertebrate genomes were investigated using a combination of sequence-based phylogenetic analyses and comparisons of synteny. We conclude that the PRL and PRL2 genes arose from a common ancestor in 1R/2R, as shown by neighboring gene families. No other gene duplicates were preserved from these tetraploidization events. The ancestral genes that would give rise to GH and PRL/PRL2 arose from an earlier duplication; most likely a local gene duplication as they are syntenic in several species. Likewise, some evidence suggests that SL arose from a local duplication of an ancestral GH/SL gene in the same time window, explaining the lack of similarity in chromosomal neighbors to GH, PRL or PRL2. Thus, the basic triplet of ancestral GH, PRL/PRL2 and SL genes appear to be unexpectedly ancient. Following 1R/2R, only SL was duplicated in the teleost-specific tetraploidization 3R, resulting in SLa and SLb. These time windows contrast with our recent report that the corresponding receptor genes GHR and PRLR arose through a local duplication in jawed vertebrates and that both receptor genes duplicated further in 3R, which reveals a surprising asynchrony in hormone and receptor gene duplications.

Characterization and expression analyses of somatolactin-α and -β genes in rare minnows (Gobiocypris rarus) following waterborne cadmium exposure

Using reverse transcription-polymerase chain reaction (RT-PCR) and RACE (rapid amplification of cDNA ends), somatolactin-α (rmSLα) and -β (rmSLβ) were identified from the pituitary gland of rare minnows (Gobiocypris rarus). The full-length cDNAs of these two genes were 1288 and 801 bp, encoding prepeptides of 250 and 228 amino acids residues, respectively. rmSLβ can be detected in the brain (including the pituitary), ovary, testis, and gill, while rmSLα was mainly expressed in the brain. On the other hand, rmSLα was expressed in all the fetal developmental stages; however, rmSLβ can just be detected in the stages since from 14 h post-fertilization (hpf). After exposure to acute waterborne cadmium (Cd), rmSLα was distinctly upregulated in juvenile rare minnows at all detected time points, from 24 to 96 h and 10 days, while rmSLβ was significantly altered only in 96 h or 10-day treatment groups. As for adults, acute Cd exposure caused alterations of both rmSLα and rmSLβ in the brain (containing the pituitary) at the 24 h; subchronic waterborne Cd treatment led to upregulation of rmSLα, while decrease of mSLβ in the brain. Alteration of rmSL transcripts following waterborne Cd exposure further confirmed the endocrine disruption of this heavy metal. Besides, exposure to as low as 5 μg/L Cd caused alteration of rmSLα, which suggested that rmSLα might be a potential biomarker for risk assessment of aquatic Cd.

Somatotropic Axis Regulation Unravels the Differential Effects of Nutritional and Environmental Factors in Growth Performance of Marine Farmed Fishes

The Gh/Prl/Sl family has evolved differentially through evolution, resulting in varying relationships between the somatotropic axis and growth rates within and across fish species. This is due to a wide range of endogenous and exogenous factors that make this association variable throughout season and life cycle, and the present minireview aims to better define the nutritional and environmental regulation of the endocrine growth cascade over precisely defined groups of fishes, focusing on Mediterranean farmed fishes. As a result, circulating Gh and Igf-i are revitalized as reliable growth markers, with a close association with growth rates of gilthead sea bream juveniles with deficiency signs in both macro- or micro-nutrients. This, together with other regulated responses, promotes the use of Gh and Igf-i as key performance indicators of growth, aerobic scope, and nutritional condition in gilthead sea bream. Moreover, the sirtuin-energy sensors might modulate the growth-promoting action of somatotropic axis. In this scenario, transcripts of igf-i and gh receptors mirror changes in plasma Gh and Igf-i levels, with the ghr-i/ghr-ii expression ratio mostly unaltered over season. However, this ratio is nutritionally regulated, and enriched plant-based diets or diets with specific nutrient deficiencies downregulate hepatic ghr-i, decreasing the ghr-i/ghr-ii ratio. The same trend, due to a ghr-ii increase, is found in skeletal muscle, whereas impaired growth during overwintering is related to increase in the ghr-i/ghr-ii and igf-ii/igf-i ratios in liver and skeletal muscle, respectively. Overall, expression of insulin receptors and igf receptors is less regulated, though the expression quotient is especially high in the liver and muscle of sea bream. Nutritional and environmental regulation of the full Igf binding protein 1-6 repertoire remains to be understood. However, tissue-specific expression profiling highlights an enhanced and nutritionally regulated expression of the igfbp-1/-2/-4 clade in liver, whereas the igfbp-3/-5/-6 clade is overexpressed and regulated in skeletal muscle. The somatotropic axis is, therefore, highly informative of a wide-range of growth-disturbing and stressful stimuli, and multivariate analysis supports its use as a reliable toolset for the assessment of growth potentiality and nutrient deficiencies and requirements, especially in combination with selected panels of other nutritionally regulated metabolic biomarkers.

EST dataset of pituitary and identification of somatolactin and novel genes in Chinese sturgeon, Acipenser sinensis

Chinese sturgeon (Acipenser sinensis) is a rare and endangered species and also an important resource for the sturgeon aquaculture industry, however, a few genes have been identified in this species. We report here construction of a pituitary cDNA library from a 24 years old female Chinese sturgeon just after its spawning, and obtained 2,025 ESTs from the library. 885 unique sequences were identified, which were categorized into 12 functional groups. More than half of the unique sequences (57%) do not match with annotated sequences in the public databases. Three of these novel genes were further identified. Notably, a full-length of cDNA (1,143 bp) encoding somatolactin of 232 amino acids was identified. Phylogenetic analysis showed 97% amino acid identity with White sturgeon somatolactin. RT-PCR analysis indicated that the somatolactin mRNA was only detected in pituitary. Pituitary-specific expression of the somatolactin suggested that the protein may play important physiological functions in pituitary-endocrine system of the Chinese sturgeon.

Activation of the black seabream (Acanthopagrus schlegeli) somatolactin-alpha gene promoter by Pit-1c in the Hepa-T1 cell-line

Somatolactin (SL) is a pituitary hormone of the growth hormone (GH) gene family found only in fish. To understand the regulation of this hormone at the level of gene transcription, we obtained a SLalpha gene from black seabream (bsb), with its 5' flanking promoter region carrying several putative transcription factors including seven binding sites for pituitary-specific transcription factor 1 (Pit-1). To study the actions of Pit-1 on this gene promoter, we cloned three variants of bsbPit-1 (Pit-1a, Pit-1b and Pit-1c) derived from alternative splicing of mRNA or differential transcription start sites from black seabream pituitary. The deduced amino acid sequences of these Pit-1s contained 371 amino acids (aa), 333 and 311aa for the three Pit-1 variants, Pit-1a, Pit-1b and Pit-1c, respectively, with diverse regions of Pit-1 located at the transactivation domain. The actions of bsbPit-1 variants on the bsbSL gene promoter were investigated using a co-transfection assay, with a reporter gene using a transient expression assay in Hepa-T1 cells. The N-terminus truncated isoform bsbPit-1c showed the highest level of activity on SLalpha gene promoter activation in Hepa-T1 cells; however, neither Pit-1a nor Pit-1b activated the bsbSL gene promoter in the same study.

cDNA cloning and isolation of somatolactin in Mozambique tilapia and effects of seawater acclimation, confinement stress, and fasting on its pituitary expression

Somatolactin (SL) is a member of the growth hormone (GH)/prolactin (PRL) family of pituitary hormones, and is found in a variety of teleost species. Somatolactin is thought to be involved in a wide range of physiological actions, including reproduction, stress response, the regulation of Ca(2+) and acid-base balance, growth, metabolism, and immune response. We report here on the cDNA structure of SL from the pituitary of Mozambique tilapia, Oreochromis mossambicus, and its gene expression in response to seawater acclimation, stress, and fasting. Tilapia SL cDNA (1573bp long) encoded a prehormone of 230 amino acids. Sequence analysis of purified SL revealed that the prehormone is composed of a signal peptide of 23 amino acids and a mature protein of 207 amino acids, which has a possible N-glycosylation site at position 121 and seven Cys residues. Tilapia SL shows over 80% amino acid identity with SLalpha of advanced teleosts such as medaka and flounder, and around 50% identity with SLbeta of carp and goldfish. Acclimation to seawater had no effect on pituitary expression of SL or on hepatic expression of the putative tilapia SL receptor (GHR1). By contrast, seawater acclimation resulted in significant increases in pituitary GH expression and in hepatic expression of tilapia GH receptor (GHR2). Confinement stress had no effect on pituitary expression of either SL or GH, or on hepatic expression of GHR1, whereas a significant increase was seen in GHR2 expression in the liver. Fasting for 4 weeks resulted in significant reductions in SL transcripts both in fresh water and seawater. It is highly likely that SL is involved in metabolic processes in tilapia along with the GH/IGF-I axis.

Grass carp somatolactin: I. Evidence for PACAP induction of somatolactin-alpha and -beta gene expression via activation of pituitary PAC-I receptors

Somatolactin (SL), the latest member of the growth hormone/prolactin family, is a novel pituitary hormone with diverse functions. At present, SL can be identified only in fish but not in tetrapods and its regulation at the pituitary level has not been fully characterized. Using grass carp as a model, we examined the direct effects of pituitary adenylate cyclase-activating polypeptide (PACAP) on SL secretion and synthesis at the pituitary cell level. As a first step, the structural identity of grass carp SL, SLalpha and SLbeta, was established by 5'/3'-rapid amplification of cDNA ends. These two SL isoforms are single-copy genes and are expressed in two separate populations of pituitary cells located in the pars intermedia. In the carp pituitary, PACAP nerve fibers were detected in the nerve tracts of the neurohypophysis and extended into the vicinity of pituitary cells forming the pars intermedia. In primary cultures of grass carp pituitary cells, PACAP was effective in stimulating SL release, cellular SL content, and total SL production. The increase in SL production also occurred with parallel rises in SLalpha and SLbeta mRNA levels. With the use of a combination of molecular and pharmacological approaches, PACAP-induced SL release and SL gene expression were shown to be mediated by pituitary PAC-I receptors. These findings, as a whole, suggest that PACAP may serve as a hypophysiotropic factor in fish stimulating SL secretion and synthesis at the pituitary level. Apparently, PACAP-induced SL production is mediated by upregulation of SLalpha and SLbeta gene expression through activation of PAC-I receptors.

Transcriptomic approach to the study of osmoregulation in the European eel Anguilla anguilla

In euryhaline teleosts, osmoregulation is a fundamental and dynamic process that is essential for the maintenance of ion and water balance, especially when fish migrate between fresh water (FW) and sea water (SW) environments. The European eel has proved to be an excellent model species to study the molecular and physiological adaptations associated with this osmoregulatory plasticity. The life cycle of the European eel includes two migratory periods, the second being the migration of FW eels back to the Sargasso Sea for reproduction. Various anatomical and physiological changes allow the successful transition to SW. The aim of this study was to use a microarray approach to screen the osmoregulatory tissues of the eel for changes in gene expression following acclimation to SW. Tissues were sampled from fish at selected intervals over a 5-mo period following FW/SW transfer, and RNA was isolated. Suppressive subtractive hybridization was used for enrichment of differentially expressed genes. Microarrays comprising 6,144 cDNAs from brain, gill, intestine, and kidney libraries were hybridized with appropriate targets and analyzed; 229 differentially expressed clones with unique sequences were identified. These clones represented the sequences for 95 known genes, with the remaining sequences (59%) being unknown. The results of the microarray analysis were validated by quantification of 28 differentially expressed genes by Northern blotting. A number of the differentially expressed genes were already known to be involved in osmoregulation, but the functional roles of many others, not normally associated with ion or water transport, remain to be characterized.

The dawn and evolution of hormones in the adenohypophysis

The adenohypophysial hormones have been believed to have evolved from several ancestral genes by duplication followed by evolutionary divergence. To understand the origin and evolution of the endocrine systems in vertebrates, we have characterized adenohypophysial hormones in an agnathan, the sea lamprey Petromyzon marinus. In gnathostomes, adrenocorticotropin (ACTH) and melanotropin (MSH) together with beta-endorphins (beta-END) are encoded in a single gene, designated as proopiomelanocortin (POMC), however in sea lamprey, ACTH and MSH are encoded in two distinct genes, proopoicortin (POC) gene and proopiomelanotropin (POM) gene, respectively. The POC and POM genes are expressed specifically in the rostral pars distalis (RPD) and the pars intermedia (PI), respectively. Consequently, the final products from both tissues are the same in all vertebrates, i.e., ACTH from the PD and MSH from the PI. The POMC gene might have been established in the early stages of invertebrate evolution by internal gene duplication of the MSH domains. The ancestral gene might be then inherited in lobe-finned fish and tetrapods, while internal duplication and deletion of MSH domains as well as duplication of whole POMC gene took place in lamprey and gnathostome fish. Sea lamprey growth hormone (GH) is expressed in the cells of the dorsal half of the proximal pars distalis (PPD) and stimulates the expression of an insulin-like growth factor (IGF) gene in the liver as in other vertebrates. Its gene consists of 5 exons and 4 introns spanning 13.6 kb, which is the largest gene among known GH genes. GH appears to be the only member of the GH family in the sea lamprey, which suggests that GH is the ancestral hormone of the GH family that originated first in the molecular evolution of the GH family in vertebrates and later, probably during the early evolution of gnathostomes. The other member of the gene family, PRL and SL, appeared by gene duplication. A beta-chain cDNA belonging to the gonadotropin (GTH) and thyrotropin (TSH) family was cloned. It is expressed in cells of the ventral half of PPD. Since the expression of this gene is stimulated by lamprey gonadotropin-releasing hormone, it was assigned to be a GTHbeta. This GTHbeta is far removed from beta-subunits of LH, FSH, and TSH in an unrooted tree derived from phylogenetic analysis, and takes a position as an out group, suggesting that lampreys have a single GTH gene, which duplicated after the agnathans and prior to the evolution of gnathostomes to give rise to LH and FSH.

Molecular cloning and characterization of growth hormone receptor and its homologue in the Japanese eel (Anguilla japonica)

Two cDNAs encoding growth hormone receptor (GHR)-like genes, eGHR1 and eGHR2, were isolated from Japanese eel (Anguilla japonica) liver tissue. The putative eel GHR proteins showed conserved structural features of vertebrate GHRs, including six cysteine residues and a YGEFS motif in the extracellular domain, a single transmembrane region, and proline-rich box 1 and box 2 domains. Northern blot analysis showed a single eGHR1 transcript in liver, while two sizes of eGHR2 transcripts, thought to be produced by alternative splicing, were present. RT-PCR revealed that eGHR1 and eGHR2 transcripts were widely distributed throughout the whole body of the Japanese eel. Moreover, the results of binding assays showed the specific binding of growth hormone to recombinant eGHR1. Since these putative eGHR proteins show all characteristics of the GHR family, we conclude that eGHR1 and eGHR2 cDNA encode two different GHRs in Japanese eel. We confirmed the ligand specificity of eGHR1 by binding assay, and further research is needed to allow characterization of the binding capability of eGHR2.

Expression of the somatolactin beta gene during zebrafish embryonic development

Somatolactin (Sl) is a pituitary hormone closely related to prolactin (Prl) and growth hormone that was until now only found in various fish species. We isolated the cDNA coding for zebrafish Slbeta and we identified the gene encoding this hormone. We also obtained a 1kb genomic fragment corresponding to the slbeta upstream promoter region. Furthermore, the slbeta expression pattern was examined during zebrafish embryogenesis using whole-mount in situ hybridization. Slbeta mRNA is first detected in a single cell at the anterior border of the neural plate starting at 23h post fertilization (hpf). Slbeta-expressing cells also express the transcription factor pit1 and are located close to prl-expressing cells. Using combined fluorescent in situ hybridization, we show that slbeta- and prl-expressing cells are clearly distinct at 29 hpf. Starting at 30 hpf, the number of slbeta positive cells increases and their location becomes more clearly distinct from lactotrope cells, in a more posterior position. At later stages (48 hpf), slbeta expression was observed posterior to growth hormone expression, again in a distinct cell type. We show that zebrafish mutants aal, as well as mutants in the pit1 gene, are deficient in slbeta expression. In conclusion, slbeta expression defines a new, additional cell type in zebrafish pituitary that depends on pit1 and aal for its differentiation.

The Multifunctional Fish Gill: Dominant Site of Gas Exchange, Osmoregulation, Acid-Base Regulation, and Excretion of Nitrogenous Waste

The fish gill is a multipurpose organ that, in addition to providing for aquatic gas exchange, plays dominant roles in osmotic and ionic regulation, acid-base regulation, and excretion of nitrogenous wastes. Thus, despite the fact that all fish groups have functional kidneys, the gill epithelium is the site of many processes that are mediated by renal epithelia in terrestrial vertebrates. Indeed, many of the pathways that mediate these processes in mammalian renal epithelial are expressed in the gill, and many of the extrinsic and intrinsic modulators of these processes are also found in fish endocrine tissues and the gill itself. The basic patterns of gill physiology were outlined over a half century ago, but modern immunological and molecular techniques are bringing new insights into this complicated system. Nevertheless, substantial questions about the evolution of these mechanisms and control remain.

CDNA cloning and sequence of European sea bass (Dicentrarchus labrax) somatolactin

Three cDNA clones encoding for European sea bass somatolactin (SL) were obtained by RT-PCR and 3' RACE of RNA of pituitary origin. Clone 1 was 582 bp in length, and included a part of the signal peptide and the 5' end of the mature protein. Clone 2 (1075 bp) included a fragment of the coding sequence and the 3' untranslated region, which was 888 bp in length and contained two putative polyadenylation signals (AATAAA) at 12-17, and 202-207 nucleotides upstream of the poly (A) tail. Clone 3 was 624 bp in length and its nucleotide sequence encoding for the entire mature protein confirmed the sequence already determined from the first two clones. The size of SL mRNA transcripts was estimated by Northern blot analysis and a single band of approximately 1.6 kb was observed with pituitary RNAs. No band was found with RNAs of brain and liver origin. Alignment of the deduced amino acid sequence revealed that European sea bass SL shared 90-84% identity with perciform, pleuronectiform and scorpaeniform fish SLs, and 77-57% with other SLs of more distant fish orders, with a strict conservation of Cys residues and the N-glycosylation site (Asn-Lys-Thr) at 121-123 amino acid positions. The reconstruction of the phylogenetic tree based on SL nucleotide sequences. and analyzed by maximum likelihood distances, showed the same clustering as the present hierarchy of fish. When comparisons were made among SL, prolactin and growth hormone of European sea bass, the overall amino identity was relatively low (22-23%). However, a high degree of amino acid homology was found at the C-terminus, which contains three of the four Cys residues strictly conserved in all the members of GH/PRL family.

Isolation and cDNA cloning of somatolactin in rabbitfish (Siganus guttatus)

We report the isolation and cDNA cloning of somatolactin (SL) from rabbitfish, Siganus guttatus. Rabbitfish SL was isolated from an alkaline extract of the pituitary glands by gel filtration chromatography on Sephadex G-100 and reversed-phase high-performance liquid chromatography. SL was monitored by immunoblotting with flounder SL antiserum. The preparation (yield: 0.86 mg/g wet tissues) contained two immunoreactive bands of 24 and 28 kDa on SDS-PAGE. Overlapping partial cDNA clones corresponding to teleost SLs were amplified by PCR from single-strand cDNA from pituitary glands. Excluding the poly(A) tail, rabbitfish SL cDNA is 1605 bp long. It contains a 693-bp open reading frame encoding a signal peptide of 24 amino acids (aa) and a mature protein of 207 aa. Rabbitfish SL has two possible N-glycosylation sites at positions 11 and 121 and seven half Cys residues. The deduced amino acid sequence shows over 80% identity with those of advanced teleosts like sea bream, red drum, and flounder, 76% with the salmonids, 57% with the eel, and 46% with the goldfish SL.

Somatolactin in the white sturgeon and African lungfish and its evolutionary significance

Somatolactin (SL) is a newly characterized pituitary hormone belonging to the growth hormone-prolactin family. Until now SL has been identified only in teleosts, the most highly derived ray-finned fishes. We report here the cloning of SL cDNAs from two species of bony fish, the white sturgeon (Acipenser transmontanus) and the African lungfish (Protopterus annectens). Overlapping partial cDNA clones corresponding to teleost SLs were amplified by polymerase chain reaction (PCR) from either single-strand or double-strand cDNA from pituitary glands. Excluding the poly(A) tail, the sturgeon SL cDNA is 881 base pairs (bp). This is comparable to 1.0 kb estimated by Northern blot analysis. It contains a 696-bp open reading frame encoding a prehormone of 232 amino acids (aa) with a signal peptide of 24 aa and a mature protein of 208 aa. Excluding the poly(A) tail, the lungfish SL cDNA is 938 bp. This is comparable to 1.1 kb estimated by Northern blot analysis. It contains a 696-bp open reading frame encoding a prehormone of 232 aa with a signal peptide of 26 aa and a mature protein of 206 aa. The deduced aa sequences of sturgeon and lungfish SLs show 76-60% and 65-54% identity with teleost SLs, respectively. These values are significantly higher than the 30% identity with nonteleostean growth hormones and prolactins. Immunostaining of sturgeon pituitary with anti-salmon SL serum demonstrated that the SL cells were localized in the pars intermedia, as in teleosts. The present results demonstrate that the SL gene is present in two divergent lineages, the Actinopterygii (Chondrostei: white sturgeon) and the Sarcopterygii (Dipnoi: African lungfish).

Cloning and phylogenetic relationship of red drum somatolactin cDNA and effects of light on pituitary somatolactin mRNA expression

The nucleotide sequence for red drum somatolactin (SL) cDNA was determined and the expression of pituitary SL mRNA was examined in red drum kept under various light conditions. A full length of SL cDNA (1629 bp) was isolated and characterized from a red drum pituitary cDNA library. The SL cDNA has an open reading frame of 696 nucleotides which encodes a 24-amino-acid signal peptide and a 207-amino-acid mature peptide. Red drum SL shares 58-87% amino acid sequence identity and 56-85% nucleotide sequence identity with other teleost SLs. The characteristic seven cysteine residues and one N-glycosylation site of SL are well conserved in the red drum SL mature peptide. Phylogenetic analysis shows that red drum SL is closely related to seabream SL and is also closely related to lumpfish, flounder, halibut, and sole SLs, whereas SLs of Atlantic cod, chum salmon, rainbow trout, and eel are more distantly related to those of the more advanced teleosts. Two SL transcripts, designated as SL I at 1.8 kb and SL II at 1.3 kb, are expressed in red drum pituitaries and correspond to two polyadenylation signal sites in red drum SL cDNA at nucleotide positions 1554 and 1270. Levels of the SL I mRNA were 2- to 4-fold higher in pituitaries of blind red drum and intact fish kept under constant darkness for 1 week than those in control fish sampled during the light phase of the light-dark cycle. Similarly, pituitary levels of SL II mRNA were 9-fold higher in blind fish and 1.6- to 4-fold higher in intact fish kept under constant darkness than in the control fish. Furthermore, these changes in mRNA levels in pituitaries were accompanied by more than 10-fold increases in SL protein concentrations in plasma. The finding that the absence of light perception for extended periods leads to dramatic increases in SL mRNA expression as well as SL secretion in red drum provides further evidence that illumination levels and SL physiology are intimately related in this species.

Studies on the GH/SL gene family: cloning of African lungfish (Protopterus annectens) growth hormone and somatolactin and toad (Bufo marinus) growth hormone

The lungfishes (lobe-finned fish) occupy a unique position in vertebrate phylogeny, being regarded as the closest extant relatives to the tetrapods. The putative pituitary hormone somatolactin (SL) has hitherto been found only in teleost fishes, and the presence of this protein in tetrapods or lobe-finned fishes has not been ascertained. It was therefore of interest to determine the structure of SL in the African lungfish (Protopterus annectens), as this information would be useful for designing probes to facilitate the detection of SL genes in amphibians and other tetrapods. The structural relationships between SL, growth hormone (GH), and prolactin (PRL) strongly suggest that these proteins evolved from a common ancestor. To obtain a more complete picture of the evolution of these hormones in lungfish, African lungfish GH has been cloned and sequenced. The cDNA sequence of a toad (Bufo marinus) GH was determined to facilitate maximum parsimony analysis of GH sequences. Cladistic analysis confirmed that lungfish and amphibian GH sequences form a clade distinct from the GH sequences of ray-finned fishes. A distance matrix analysis of SL sequences indicated that lungfish SL had the lowest primary sequence identity with goldfish SL (47%) and the highest with flounder SL (66%). The detection of SL in a lungfish indicates that the gene duplication within the SL/GH/PRL family, which gave rise to SL, must have occurred in a common ancestor of the ray-finned fishes (Actinopterygii) and the lungfishes (Sarcopterygii) and tetrapods.