The fate of granulosa cells following premature oocyte loss and the development of ovarian cancers.

This review examines the importance of the epithelial origin of granulosa cells and their possible contribution to the development of ovarian cancers in three animal models. We hypothesise that undifferentiated granulosa cells, devoid of their germ cell regulator, retain their embryonic plasticity and may give rise to ovarian cancers of epithelial origin. Dazl-KO and FancD2-KO mice and BMP15-KO sheep are animal models in which germ cells or oocytes are lost at specific stages of follicular formation or growth, leaving behind clusters of residual, but healthy somatic cells. A common feature in Dazl- and Fancd2-KO animals following germ cell/oocyte loss is the presence of sex cords and intraovarian epithelial ducts or tubules. In Dazl-KO mice, cord/tubule-like structures, OSE invaginations and clusters of steroidogenic cells became increasingly prominent with age, but these abnormal structures remained benign. In Fancd2-KO mice, the formation of sex-cords and intraovarian tubules lead to the formation of tumours with multiple phenotypes including luteomas, papillary cysts and malignant carcinomas (e.g. adenocarcinomas). In BMP15-KO sheep, oocytes die as follicles start to grow, leaving 'nodules' containing granulosa cells with a capacity to respond to follicle stimulating hormone and synthesize inhibin. Thereafter, these nodules coalesced and a range of benign solid or semi-solid tumour phenotypes developed. We conclude that premature loss of oocytes, but not granulosa cells, leads to tumour formation with multiple phenotypes. Moreover, the severity of tumour development is linked to both the specificity of the mutation and the timing of oocyte loss relative to that of follicular formation.

Secretoneurin stimulates the production and release of luteinizing hormone in mouse L{beta}T2 gonadotropin cells.

Secretoneurin (SN) is a functional secretogranin II (SgII)-derived peptide that stimulates luteinizing hormone (LH) production and its release in the goldfish. However, the effects of SN on the pituitary of mammalian species and the underlying mechanisms remain poorly understood. To study SN in mammals, we adopted the mouse LßT2 gonadotropin cell line that has characteristics consistent with normal pituitary gonadotrophs. Using radioimmunoassay and real-time RT-PCR, we demonstrated that static treatment with SN induced a significant increment of LH release and production in LßT2 cells in vitro. We found that GnRH increased cellular SgII mRNA level and total SN-immunoreactive protein release into the culture medium. We also report that SN activated the extracellular signal-regulated kinases (ERK) in either 10-min acute stimulation or 3-h chronic treatment. The SN-induced ERK activation was significantly blocked by pharmacological inhibition of MAPK kinase (MEK) with PD-98059 and protein kinase C (PKC) with bisindolylmaleimide. SN also increased the total cyclic adenosine monophosphate (cAMP) levels similarly to GnRH. However, SN did not activate the GnRH receptor. These data indicate that SN activates the protein kinase A (PKA) and cAMP-induced ERK signaling pathways in the LH-secreting mouse LßT2 pituitary cell line.

Gonadotrope and thyrotrope development in the human and mouse anterior pituitary gland.

Genes and orthologous intrinsic and extrinsic factors critical for embryonic pituitary gonadotrope and thyrotrope cell differentiation have been identified mainly in rodents, but data on the human are very limited. In human fetal pituitaries examined between 14 and 19 weeks of gestation using immunofluorescent confocal microscopy, we found that most fetal gonadotropes expressed alpha-GSU, LHbeta, and FSHbeta gonadotropin subunits while almost no cells expressed alpha-GSU and LHbeta alone. Gonadotropes expressing alpha-GSU and FSHbeta only were detected in both male and female pituitaries, increasing in proportion to total gonadotropes in both males and females from 14 (approximately 4.5%) to 19 weeks (approximately 16.5%) with a peak in males of 45.5% compared with females of 16.5% at 17 weeks of gestation. When FSHbeta or LHbeta genes were expressed, gonadotropes were non-dividing. This profile of human fetal gonadotrope development differs from the current mouse model. Furthermore, while expression of alpha-GSU appears to be the lead protein in gonadotropes, in thyrotropes which ultimately express alpha-GSU with TSHbeta, we observed that most if not all thyrotropes were TSHbeta-positive but alpha-GSU-negative until around 19 weeks in human, and e15 in mouse, fetal pituitaries. Furthermore, the TSHbeta-only thyrotropes were dividing, and TSHbeta rather than alpha-GSU was the lead protein in thyrotrope development. Thus, while biologically active dimeric FSH and LH can be produced by the human fetal pituitary by 14 weeks, dimeric biologically active TSH will only be produced from around 17 weeks of gestation. The mechanism(s) responsible for the different molecular regulation of alpha-GSU gene expression in gonadotropes and thyrotropes in the developing human fetal pituitary now requires investigation.