Cloning of cDNA encoding the common alpha subunit precursor molecule of pituitary glycoprotein hormones in the Australian lungfish, Neoceratodus forsteri

Pituitary Glycoprotein Hormone β Subunits in the Australian Lungfish and Estimation of the Relative Evolution Rate of These Subunits Within Vertebrates1

The beta subunits of the two pituitary gonadotropins LH and FSH and of thyroid-stimulating hormone (TSH) were cloned from Australian lungfish (Neoceratodus forsteri) pituitary glands. These three glycoprotein hormone beta subunits possess the main characteristics common to their counterparts in other vertebrates. Taking advantage of the phylogenetic position of the lungfish, close to the root of tetrapods, a maximum parsimony tree was inferred from these new sequences and sequences from representatives of the diversity of vertebrates. The topology of the tree was imposed so that it reflected as closely as possible the real evolutionary history of the subunits. This tree was used to estimate the relative evolution rate of the three subunits in vertebrates. Cumulated amino acid substitutions from the basal subunit node (ancestral subunit sequence) to the species node were calculated and compared. It showed that a burst in evolutionary rate occurred for the LHbeta subunit in the tetrapod lineage sometime after the emergence of amphibians. The rate of evolution of the LHbeta subunit was particularly high throughout the radiation of mammals while FSH and TSHbeta subunits kept quite stable in this lineage. A burst in evolutionary rate was also observed for the FSHbeta subunit in the lineage leading to teleosts sometime after the emergence of chondrosteans and the dynamic of evolution was high throughout the radiation of teleosts. These results were consistent with data obtained from pairwise comparisons.

Cloning of complimentary deoxyribonucleic acid encoding follicle-stimulating hormone and luteinizing hormone beta subunit precursor molecules in Reeves's turtle (Geoclemys reevesii) and Japanese grass lizard (Takydromus tachydromoides)

Reptilia is the only vertebrate class in which cDNA for the gonadotropin beta subunit precursor molecule has not been cloned. We have isolated the full-length cDNA clone encoding the LH beta subunit precursor molecule and a partial cDNA clone encoding the FSH beta subunit precursor molecule from a pituitary cDNA library of Reeves's turtle. We further clarified the nucleotide sequence of the remaining part of the turtle FSH beta cDNA and that of full-length cDNA encoding the LH beta subunit precursor molecule of the Japanese grass lizard, by means of the 5' rapid amplification of cDNA end (RACE) and 3' RACE. The nucleotide sequence of the turtle FSH beta cDNA we determined was 584 bp long and contained the coding sequence, 5' untranslated region (UTR) and 3' UTR of 396, 34, and 154 bp, respectively. The nucleotide sequence of the turtle LH beta we isolated was 498 bp long and contained the coding sequence, 5' UTR and 3' UTR of 420, 7, and 71 bp, respectively. The nucleotide sequence of the lizard LH beta we determined was 537 bp long and contained the coding sequence, 5' UTR and 3' UTR of 441, 35, and 61 bp, respectively. Amino acid sequences deduced from coding regions of the turtle FSH beta, LH beta and the lizard LH beta were 131, 139, and 146 residues, respectively. Referring to the amino acid sequences of the bullfrog FSH and LH beta subunit molecules determined chemically, we deduced the amino acid sequences of mature peptide. Amino acid sequences of mature peptides of the turtle FSH, turtle LH, and the lizard LH were 111, 112, and 112 residues, respectively. Amino acid sequences of the mature peptides were compared with those of other vertebrates. The amino acid sequence of the turtle FSH beta subunit molecule was 84.7-85.6, 67.8-71.4, and 61.3-62.2% identical to the FSH sequence of birds, mammals, and amphibians, respectively. The amino acid sequence of the turtle LH beta subunit molecule was 51.6-54.6, 36.2-48.7, and 56.3-57.5% identical to the LH sequence of birds, mammals, and amphibians, respectively. The amino acid sequence of the lizard LH beta subunit molecule was 39.1-47.1, 32.9-43.0, and 46.0-47.3% identical to the LH sequence of birds, mammals, and amphibians, respectively. These identity values suggest that the turtle or reptilian FSH beta subunit molecule is more closely related to avian and mammalian FSH beta subunit molecules than to amphibian FSH beta subunit molecules but reptilian LH beta subunit molecules are more closely related to amphibian LH beta subunit molecules than to avian and mammalian LH beta subunit molecules. This discrepancy in the molecular similarity relationship found in the reptilian FSH and LH beta subunit molecules can be interpreted by assuming that evolution speed was not the same among hormone species and also among vertebrate groups.

Cloning of the genes for the pituitary glycoprotein hormone alpha and follicle-stimulating hormone beta subunits in the Japanese crested ibis, Nipponia nippon

We have isolated a part of the gene for the pituitary glycoprotein hormone common alpha subunit (PGHalpha) and the whole gene for the follicle-stimulating hormone beta subunit (FSHbeta) in the Japanese crested ibis (Nipponia nippon), a critically endangered bird species in East Asia. The nucleotide sequence of a part of the PGHalpha gene (5026 bp) contained three exons holding the whole coding and 3' untranslated regions, but lacked a 5' untranslated region. Its exon-intron structure was similar to that in mammals, but different from that in teleosts in the location of the second intron. For the FSHbeta gene, the nucleotide sequence of 7633 bp was assembled from two phage clones. The exon-intron structure of three exons and two introns was similar to that observed in mammals and teleosts. In the putative promoter region of the ibis FSHbeta gene, a progesterone responsive element (PRE)-like sequence and two AP-1 responsive element-like sequences reported in the ovine FSHbeta gene were not conserved in complete form. The increased number of ATTTA motifs in the putative 3' untranslated region in comparison with those in Japanese quail and chicken FSHbeta cDNA suggested that more rapid degradation of FSHbeta mRNA occurs in this species. Deduced amino acid sequences of the ibis PGHalpha and FSHbeta showed high similarities with those of the corresponding subunits of other avian species. This is the first report on the genomic sequences of the PGHalpha and FSHbeta in an avian species.

Purification and characterization of insulin from the Australian lungfish, Neoceratodus forsteri (Dipnoi)

The Australian lungfish Neoceratodus forsteri, a facultative air breather, is considered to be the most primitive of the extant Dipnoi and so occupies a uniquely important evolutionary position in the transition from fish to tetrapods. Insulin was isolated from an extract of the pancreas of N. forsteri and its primary structure established as: A-Chain, Gly-Ile-Val-Glu-Gln-Cys-Cys-His-Thr-Pro(10)-Cys-Ser-Leu-Tyr-Gln-Leu-G lu-Asn-Tyr-Cys(20)-Asn-Glu-Thr-Glu; B-Chain, Ala-Ala-Val-Asn-Gln-His-Leu-Cys-Gly-Ser(10)-His-Leu-Val-Glu-Ala-Leu- Tyr-Phe-Val-Cys(20)-Gly-Glu-Arg-Gly-Phe-Phe-Tyr-Leu-Pro- Lys(30)-Gly. This amino acid sequence is more similar to that of human insulin than to insulins from present-day amphibians. All the residues in human insulin that are considered to be important in receptor binding, dimerization, and hexamerization are conserved in lungfish insulin except for the substitution (Leu --> Phe) at the position corresponding to B17 in human insulin. Consistent with the assertion that the Dipnoi is a monophyletic group, insulins from N. forsteri and from the African lungfish Protopterus annectens contain extensions to the C-terminus of the A-chain and to the N-terminus of the B-chain that have not been found in other sarcopterygian species. However, the unusual amino acid substitutions found in insulin from P. annectens (e.g., GlyB21 --> Ala, GluB22 --> Asp, and ArgB23 --> Asn) are not present in N. forsteri insulin, suggesting that they occurred in the Protopterus lineage after divergence of the genera.

Teleost-type angiotensin is present in Australian lungfish, Neoceratodus forsteri

Angiotensin I (ANG I) was produced from the incubation of lungfish plasma with homologous kidney extracts. The purified peptide was found to have the sequence of H-Asn-Arg-Val-Tyr-Val-His-Pro-Phe-Thr-Leu-OH, which is homologous for the first eight residues with all teleost angiotensins so far sequenced, although lungfish generally possess tetrapod-type hormones. The lungfish decapeptide (ANG I) induced dose-dependent increases in arterial pressure in the rat. The lungfish octapeptide (ANG II) released aldosterone from kidney-adrenal tissue in vitro in a dose-dependent manner and induced dose-dependent increases in arterial pressure of the lungfish. Substitution of asparagine with aspartic acid in the first position (tetrapod-type ANG II) did not alter the blood pressure response significantly, but a second substitution of the valine in the (5)-position with isoleucine (ANG II form found in human and rat) abolished the rise in arterial pressure in lungfish over the same dose range.

Cloning of cDNAs for the pituitary glycoprotein hormone alpha subunit precursor molecules in three amphibian species, Bufo japonicus, Rana catesbeiana, and Cynops pyrrhogaster

We have isolated cDNA clones encoding molecules of putative glycoprotein hormone alpha subunit precursors from their pituitary cDNA libraries for a toad, bullfrog and newt. The insert of the isolated toad cDNA was 562 bp long containing the 5'-untranlated, coding and 3'-untranslated regions of 38, 363 and 161 bp, respectively. The insert of the bullfrog cDNA was 604 bp long containing the 5'-untranslated, coding and 3'-untranslated regions of 70, 366, and 168 bp, respectively. In the newt, a composite cDNA sequence was estimated from four isolated partial clones. It was 694 bp long and contained the 5'-untranslated region of 89 bp, coding region of 366 bp, and 3'-untranslated region of 91 bp or longer. Amino acid sequences deduced from coding regions of the isolated clones showed that the signal peptides consist of 24 residues and the mature proteins of 96 (toad) or 97 residues (bullfrog and newt). In all three species, an insertion of an amino acid residue was found between residues 26 and 27 of the alpha subunit molecule sequence of all other vertebrate species studied. Interestingly, the percentage identities of the entire amino acid sequence between amphibian and mammalian (or avian) alpha subunits are lower than those between lungfish and mammalian (or avian) alpha subunits. This suggests that amino acid substitutions have occurred more frequently during the course of evolution in the alpha subunit molecule of amphibians than in that of other tetrapod vertebrates, although the biological significance of this is not known.