Evolution of gonadotropin structure and function

Luteinizing Hormone is an effective replacement for hCG to induce ovulation in Xenopus

Injection of human Chorionic Gonadotropin (hCG) directly into the dorsal lymph sac of Xenopus is a commonly used protocol for induction of ovulation, but recent shortages in the stocks of commercially available hCG as well as lack of a well tested alternative have resulted in frustrating experimental delays in laboratories that predominantly use Xenopus in their research. Mammalian Luteinizing Hormones (LH) share structural similarity, functional equivalency, and bind the same receptor as hCG; this suggests that LH may serve as a good alternative to hCG for promoting ovulation in Xenopus. LH has been found to induce maturation of Xenopus oocytes in vitro, but whether it can be used to induce ovulation in vivo has not been examined. Here we compared the ability of four mammalian LH proteins, bovine (bLH), human (hLH), ovine (oLH), porcine (pLH), to induce ovulation in Xenopus when injected into the dorsal lymph sac of sexually mature females. We find that both ovine and human LH, but not bovine or porcine, are good substitutes for hCG for induction of ovulation in WT and J strain Xenopus laevis and Xenopus tropicalis.

A human FSHB transgene encoding the double N-glycosylation mutant (Asn(7Δ) Asn(24Δ)) FSHβ subunit fails to rescue Fshb null mice

Follicle-stimulating hormone (FSH) is a gonadotrope-derived heterodimeric glycoprotein. Both the common α- and hormone-specific β subunits contain Asn-linked N-glycan chains. Recently, macroheterogeneous FSH glycoforms consisting of β-subunits that differ in N-glycan number were identified in pituitaries of several species and subsequently the recombinant human FSH glycoforms biochemically characterized. Although chemical modification and in vitro site-directed mutagenesis studies defined the roles of N-glycans on gonadotropin subunits, in vivo functional analyses in a whole-animal setting are lacking. Here, we have generated transgenic mice with gonadotrope-specific expression of either an HFSHB(WT) transgene that encodes human FSHβ WT subunit or an HFSHB(dgc) transgene that encodes a human FSHβ(Asn7Δ 24Δ) double N-glycosylation site mutant subunit, and separately introduced these transgenes onto Fshb null background using a genetic rescue strategy. We demonstrate that the human FSHβ(Asn7Δ 24Δ) double N-glycosylation site mutant subunit, unlike human FSHβ WT subunit, inefficiently combines with the mouse α-subunit in pituitaries of Fshb null mice. FSH dimer containing this mutant FSHβ subunit is inefficiently secreted with very low levels detectable in serum. Fshb null male mice expressing HFSHB(dgc) transgene are fertile and exhibit testis tubule size and sperm number similar to those of Fshb null mice. Fshb null female mice expressing the mutant, but not WT human FSHβ subunit-containing FSH dimer are infertile, demonstrate no evidence of estrus cycles, and many of the FSH-responsive genes remain suppressed in their ovaries. Thus, HFSHB(dgc) unlike HFSHB(WT) transgene does not rescue Fshb null mice. Our genetic approach provides direct in vivo evidence that N-linked glycans on FSHβ subunit are essential for its efficient assembly with the α-subunit to form FSH heterodimer in pituitary. Our studies also reveal that N-glycans on FSHβ subunit are essential for FSH secretion and FSH in vivo bioactivity to regulate gonadal growth and physiology.

Cloning and Expression of Iranian Turkmen-thoroughbred Horse Follicle Stimulating Hormone in Pichia pastoris

BACKGROUND

Follicle stimulating hormone (FSH) plays an essential role in reproductive physiology and follicular development.

OBJECTIVE

A new variant of the equine fsh (efsh) gene was cloned, sequenced, and expressed in Pichia pastoris (P. pastoris) GS115 yeast expression system.

MATERIALS AND METHODS

The full-length cDNAs of the efshα and efshβ chains were amplified by reverse transcription polymerase chain reaction (RT-PCR) using the total RNA isolated from an Iranian Turkmen-thoroughbred horse's anterior pituitary gland. The amplified efsh chains were cloned into the pPIC9 vector and transferred into P. pastoris. The secretion of recombined eFSH using P. pastoris expression system was confirmed by Western blotting and immunoprecipitation (IP) methods.

RESULTS

The DNA sequence of the efshβ chain accession number JX861871, predicted two putative differential nucleotide arrays, both of which are located in the 3'UTR. Western blotting showed a molecular mass of 13 and 18 kDa for eFSHα and eFSHβ subunits, respectively. The expression of desired protein was confirmed by protein G immunoprecipitation kit.

CONCLUSIONS

eFSH successfully expressed in P. pastoris. These findings lay a foundation to improve ovulation and embryo recovery rates as well as the efficiency of total embryo-transfer process in mares.

Models of glycoprotein hormone receptor interaction

The glycoprotein hormones regulate reproduction and development through their interactions with receptors in ovarian, testicular, and thyroid tissues. Efforts to design hormone agonists and antagonists useful for treat-ing infertility and hyperthyroidism would benefit from a molecular understanding of hormone-receptor interaction. The structure of a complex containing FSH bound to a fragment of its receptor has been determined at 2.9 Angstroms resolution, but this does not explain several observations made with cell-surface G protein receptors and may reflect the manner in which FSH binds a short alternate spliced receptor form. We discuss observations that must be explained by any model of the cell-surface G protein-coupled glycoprotein hormone receptors and suggest structures for these receptors that satisfy these requirements. Glycoprotein hormones appear to contact two distinct sites in the extracellular domains of their receptors, not just the leucine-rich repeat domain. These dual contacts contribute to ligand binding specificity and appear to be essential for signal transduction. As outlined in this minireview, differences in the manners in which these ligands contact their receptors explain why some ligands and ligand analogs interact with more than one class of receptor and why some receptors and receptor analogs bind more than one ligand. The unique manner in which these ligands appear to interact with their receptors may have facilitated hormone and receptor co-evolution during early vertebrate speciation.

cDNA cloning of the beta subunit of teleost thyrotropin

cDNA clones encoding the beta subunit of thyrotropin (thyroid-stimulating hormone; TSH) were isolated from a cDNA library made from the pituitaries of immature rainbow trout and sequenced. The precursor of rainbow trout TSH beta consists of 147 aa, which can be cleaved into a signal peptide (20 aa) and a mature protein (127 aa) containing one potential N-glycosylation site and 12 cysteine residues. The protein showed highest homology with human TSH beta (51%) and lesser homology with human follitropin (42%), human lutropin (32%), and salmon gonadotropin (31-33%) beta subunits. The identification of TSH in addition to two gonadotropins (gonadotropins I and II) in the teleost fish suggests that the divergence of three kinds of glycoprotein hormones from an ancestral molecule took place earlier than the time of divergence of teleosts from the main line of evolution leading to tetrapods. Northern blot analysis showed that the expression of the rainbow trout TSH beta gene is specific to the pituitary gland and is significantly higher in immature fish than in mature fish, suggesting that TSH plays some role in the biological processes of immature fish.

Molecular structures of glycoprotein hormones and functions of their carbohydrate components

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Arginine-vasotocin and gonadal activity in the lizard, Podarcis s. sicula Raf

Arginine-vasotocine (AVT) injected into male adult lizards, Podarcis s. sicula Raf., inhibits the last phases of spermatogenesis and the endocrine activity of gonads. In female lizards the substance induces an early interruption of egg deposition.