Identification of a functional corpus luteum in the Atlantic hagfish, Myxine glutinosa

Molecular cloning of cytochrome P450 side-chain cleavage and changes in its mRNA expression during gonadal development of brown hagfish, Paramyxine atami

Since hagfishes are considered the most primitive vertebrate known, extant or extinct, studies on their reproduction are indispensable for understanding phylogenetic aspects of vertebrate reproduction. However, little information is available on the endocrine regulation of the gonadal function in the hagfish. Based on EST analysis of the testis of the brown hagfish (Paramyxine atami), P450 side chain cleavage (CYP11A), which is the first and essential enzyme for steroidogenesis in jawed vertebrates, was cloned. The deduced amino acid sequence of hagfish CYP11A shows high identity to other animal forms especially in two functional domains, adrenodoxin binding domain and heme-binding domain. In the phylogenetic analysis, hagfish CYP11A forms a clade with the vertebrate CYP11A. Following the real-time PCR analysis, CYP11A mRNA expression levels were clearly correlated to the developmental stages of gonads in both sexes of the brown hagfish. By in situ hybridization, CYP11A mRNA signals were found in the theca cells of the ovarian follicles and Leydig cells and the tubule-boundary cells of the testis. These molecular and histological evidences are suggesting that CYP11A plays functional roles as a steroidogenic enzyme in gonadal development. Moreover, native GTH purified from hagfish pituitary stimulated the transcriptional levels of CYP11A in the organ-cultured testis in vitro, clearly suggesting that the steroidogenic activity of the hagfish is under the control of the pituitary GTH. It is suggested that vertebrates, during their early evolution, have established the pituitary-gonadal reproductive system.

Relationships between plasma concentrations of sex steroid hormones and gonadal development in the brown hagfish, Paramyxine atami

The relationship between sex steroid hormone profiles in plasma and gonadal function in hagfish is poorly understood. In the present study, plasma concentrations of estradiol, testosterone, and progesterone were examined with respect to gonadal development, sexual differences, and possible function of atretic follicles in the brown hagfish, Paramyxine atami, using a time-resolved fluoroimmunoassay. Plasma concentrations of these three hormones were low in juveniles of both sexes. In females, plasma estradiol showed a significant correlation with ovarian development, with the highest concentrations in late vitellogenic adults. Plasma testosterone and progesterone also increased significantly in non-vitellogenic adult females; however, plasma testosterone showed no significant differences among adult females at different ovarian developments, while plasma progesterone was significantly lower in late vitellogenic adults than it was in non-vitellogenic adults. Vitellogenic females that possessed atretic follicles showed significantly lower concentrations of all three hormones than females that only possessed normal follicles. In males, no significant differences were found in plasma estradiol or testosterone levels among groups of different developmental stages of the testis, while plasma progesterone showed a clear inverse relationship with testicular development. Thus, differences were found in plasma sex steroid hormone profiles between male and female P. atami. Moreover, plasma estradiol showed a significant correlation with ovarian development, which suggests that estradiol is involved in the regulation of ovarian development. The present study also revealed that steroid hormone production was strongly suppressed in females that possessed atretic follicles in their ovaries.

Effects of estradiol or testosterone treatment on expression of gonadotropin subunit mRNAs and proteins in the pituitary of juvenile brown hagfish, Paramyxine atami

A single functional gonadotropin (GTH) comprising two subunits, α and β, was recently identified in the pituitary of brown hagfish (Paramyxine atami). Little is known about the feedback mechanisms that regulate these GTH subunits by sex steroids in the hagfish. The present study was designed to examine feedback effects of estradiol and testosterone on mRNA expression and protein expression of both GTHα and GTHβ subunits in the pituitary of the juvenile P. atami. Intraperitoneal administration of estradiol over the course of 27days resulted in substantial accumulation of immunoreactive (ir)-GTHα and ir-GTHβ in the adenohypophysis, but testosterone treatments over 27days had no effects on ir-GTHα or ir-GTHβ. Estradiol treatment for 1, 2, 4 or 14days had no effect on GTHα mRNA levels. In contrast, after 2days of estradiol treatment, GTHβ mRNA levels had increased significantly from baseline, while these levels were not affected after treatment over 1, 4, or 14days. After 14days of testosterone treatment, both GTHα and GTHβ mRNA levels had decreased significantly from baseline levels. These results indicate that estradiol acted primarily to suppress the secretion of GTH, and hence resulted in the accumulations of ir-GTHα and ir-GTHβ in the pituitary. On the other hand, testosterone appeared to suppress both the synthesis and the secretion of GTH. Thus, estradiol and testosterone probably differ in their effects on the regulation of pituitary GTH synthesis and secretion in juvenile hagfish.

Patterns of oocyte development in natural habitat and captive Salminus hilarii Valenciennes, 1850 (Teleostei: Characidae)

Fecundity and oocyte development in Salminus hilarii female brood stock were analyzed with the aim of investigating the impact of migration impediment on oogenesis. Histological analyses of the ovaries were performed in adult females caught in two different environments--the Tietê River (natural) and captivity--and the gonadossomatic index, oocyte diameter and fecundity determined. Five germ cell development stages (oogonium, perinucleolar, cortical alveoli, vitellogenic, ripe) and two other structures (postovulatory follicles and atretic oocytes) were observed in females caught in the river. Captive animals lacked the ripe oocytes and postovulatory follicles and had a relatively higher number of atretic oocytes. Females in captivity are known to produce larger oocytes, and they release fewer eggs in each spawn (absolute fecundity) when compared with animals that are able to migrate. Our results suggest that the Tietê River is undergoing alterations which are being reflected in the reproductive performance of S. hilarii, mainly due to the presence of atretic oocytes in females caught in the river. The lack of postovulatory follicles and ripe oocytes in captive animals reveals that migratory impediment negatively impacts final oocyte maturation. However, the stage of maturation reached is adequate for ovulation induction with hormone manipulation.

Sex steroids and their receptors in lampreys

The use of steroids and their receptors as ligand-gated transcription factors is thought to be an important step in vertebrate evolution. The lamprey is the earliest-evolving vertebrate to date in which sex steroids and their receptors have been demonstrated to have hormonal roles similar to those found in jawed vertebrates. Sex steroids and their receptors have been examined in several lamprey species, and the majority of studies have focused on the sea lamprey, Petromyzon marinus. While classical steroids appear to be present in lampreys, their function, concentrations, and synthesis have not been determined conclusively. The only classical steroid that is thought to act as a hormone in both males and females is estradiol. Recent research has established that lampreys produce and circulate 15alpha-hydroxylated steroids, and that these steroids respond to upstream stimulation within the hypothalamic-pituitary-gonadal axis. In particular, 15alpha-hydroxyprogesterone is highly sensitive and responds in great magnitude to stimulation, and is likely a hormone. Lampreys also appear to use androstenedione, a precursor to vertebrate androgens, as their main androgen, and a receptor for androstenedione has recently been described. Non-classical steroids are prevalent in many aquatic vertebrates, and the non-classical steroids found in the sea lamprey may represent an evolutionary artifact, or alternatively may be a way to avoid endocrine disruption when ingesting the body fluids of host fish. The lamprey will continue to be an interesting model for examining the evolution of steroid hormones, steroid receptors, and steroid function.