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Gene expression and secretion of luteinising hormone and follicle-stimulating hormone in relation to gene expression of gonadotrophin-releasing hormone receptors in the brushtail possum (Trichosurus vulpecula) demonstrates highly conserved mechanisms.

J Crawford, School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand
D Heath, School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand
L Haydon, School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand
B Thomson, School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand
D Eckery, School of Biological Sciences, Victoria University of Wellington, Wellington, New Zealand

Correspondence: Janet Crawford, Email: janet.crawford{at}vuw.ac.nz

Abstract

In eutherian mammals, the gonadotrophins (LH and FSH), are synthesized and stored in gonadotroph cells under the regulation of multiple mechanisms including GnRH. Very little is known about the regulation of gonadotrophin secretion and storage in pituitary glands of marsupials. This study revealed, using quantitative PCR and heterologous RIA techniques, that LHB mRNA expression levels remained constant over the oestrous cycle, regardless of the presence of a preovulatory LH surge which is characteristic of a hormone secreted under regulation. Our sampling regime was unable to detect pulses of LH during the follicular phase although GNRHR mRNA levels had increased at this time. Pulses of LH were however detected in the luteal phase of cycling females, in anoestrus females and in males. There was a positive correlation between gene expression of FSHB and plasma levels of FSH at different stages of the oestrous cycle and no pulses of FSH were detected at any time; all characteristics of a hormone secreted via the constitutive pathway. Using in situ hybridisation and immunohistochemistry methods, we determined that mRNA expression of LHB and FSHB, and protein storage of gonadotrophins exhibited a similar pattern of localisation within the pituitary gland. Additionally sexual dimorphism of gonadotroph populations was evident. In summary, these findings are similar to that reported in eutherians and considering that marsupial evolution diverged from eutherians over 100 million years ago suggests that the regulation of gonadotrophins is highly conserved indeed.