Stem cell-derived in vitro models for investigating the effects of endocrine disruptors on developing neurons and neuroendocrine cells.

Neuroendocrine cells are a set of specialized hormone-releasing neurons that control most vital functions in humans and wildlife, such as growth, reproduction, metabolism, and stress responses. Increasing evidence points to neuroendocrine cells as the primary neuronal target of endocrine disruptors. Endocrine disruption appears to be most significant during prenatal and early postnatal development.

Intermolecular interactions of homologs of germ plasm components in mammalian germ cells.

In some species such as flies, worms, frogs and fish, the key to forming and maintaining early germ cell populations is the assembly of germ plasm, microscopically distinct egg cytoplasm that is rich in RNAs, RNA-binding proteins and ribosomes. Cells which inherit germ plasm are destined for the germ cell lineage. In contrast, in mammals, germ cells are formed and maintained later in development as a result of inductive signaling from one embryonic cell type to another.

Decreased gonadotropin-releasing hormone neuronal activity is associated with decreased fertility and dysregulation of food intake in the female GPR-4 transgenic rat.

Expression of a cAMP-specific phosphodiesterase in GnRH neurons in the GPR-4 transgenic rat resulted in decreased LH levels and pulse frequency and diminished fertility. We have characterized changes in fertility, adiposity, and reproductive and metabolic hormones with age. Although LH levels were decreased in 3-, 6-, and 9-month-old GPR-4 females relative to wild-type (WT) controls, GPR-4 females did not become anovulatory until 6 months of age.

Targeted expression of a dominant-negative fibroblast growth factor (FGF) receptor in gonadotropin-releasing hormone (GnRH) neurons reduces FGF responsiveness and the size of GnRH neuronal population.

Increasing evidence suggests that fibroblast growth factors (FGFs) are neurotrophic in GnRH neurons. However, the extent to which FGFs are involved in establishing a functional GnRH system in the whole organism has not been investigated. In this study, transgenic mice with the expression of a dominant-negative FGF receptor mutant (FGFRm) targeted to GnRH neurons were generated to examine the consequence of disrupted FGF signaling on the formation of the GnRH system.

Pulsatile luteinizing hormone and follicle-stimulating hormone secretion and gonadotropin subunit mRNA levels in the ovariectomized GPR-4 transgenic rat.

Genetic targeting of the cAMP-specific phosphodiesterase 4D1 (PDE4D1) to gonadotropin-releasing hormone (GnRH) neurons in the GPR-4 transgenic rat resulted in decreased luteinizing hormone (LH) pulse frequency in castrated female and male rats. A similar decrease in the intrinsic GnRH pulse frequency was observed in GT1 GnRH cells expressing the PDE4D1 phosphodiesterase. We have extended these findings in ovariectomized (OVX) GPR-4 rats by asking what effect transgene expression had on pulsatile LH and follicle-stimulating hormone (FSH) secretion, plasma and pituitary levels of LH and FSH, and levels of the alpha-glycoprotein hormone subunit (alpha-GSU), LH-beta and FSH-beta subunit mRNAs.

Phosphodiesterase expression targeted to gonadotropin-releasing hormone neurons inhibits luteinizing hormone pulses in transgenic rats.

Experiments in the GT1 gonadotropin-releasing hormone (GnRH) cell line have shown that the cAMP signaling pathway plays a central role in regulating the excitability of the cells. Lowering cAMP levels by expressing the constitutively active cAMP-specific phosphodiesterase PDE4D1 in GT1 cells inhibited spontaneous Ca2+ oscillations and intrinsic pulsatile GnRH secretion. To address the role of cAMP levels in endogenous GnRH neurons, we genetically targeted expression of PDE4D1 (P) to GnRH neurons in transgenic rats (R) by using the GnRH gene promoterenhancer regions (G).

Localization of olfactory cyclic nucleotide-gated channels in rat gonadotropin-releasing hormone neurons.

The GT1 GnRH cell lines express all three subunits of the cyclic nucleotide-gated (CNG) channels (CNG2, 4.3 and 5) expressed in olfactory neurons. We investigated using in situ hybridization and double immunofluorescence whether endogenous GnRH neurons in therat also express CNG channel subunits.