GnRH

Master controller of reproduction Gene on chromosome 8 23 isoforms in vertebrates Most vertebrates- GnRH I (GnRH) and GnRH II Roles include: Neuroendocrine - HPG Paracrine (placenta/gonads) Autocrine (prostate/breast cancer) Neurotransmitter (Regions of the brain)

Pre-pro hormone Cleavage steps-= Mature GnRH and GAP Structure from left to right is: Signal peptide, GnRH, GnRH associated peptide GAP peptide- co-secreted with GnRH, unknown function

Embryonic period: Originate outside CNS, in medial olfactory placode Cells migrate Nasal region  brain  medio-basal hypothalamus Numerous genes involved

Known mutations causing HH KAL1, FGFR1, FGF8, PROK2, PROKR2, NELF, CHD7, GNRH1, GNRHR, GPR54, TAC3, TAC3R, NKB/NK3R, WDR11

Mutation in KAL-1 gene Premature termination of migration  anosmia & hypogonadotrophic hypogonadism

GnRH is processed and packaged into storage granules that are transported down the axons to the external zone of the median eminence. GnRH released in synchronized pulses from the GnRH nerve endings into hypophyseal portal system. Rhythmic pulses- every 30-120 minutes – “circhoral pulses” GnRH Pulse generator collection of hypothalamic neurons producing endogenous secretory rhythms GnRH t1/2 2-4 minutes GnRH stimulates synthesis and secretion of gonadotrophins. Differential frequency and amplitude alter pattern of FSH and LH secretion, therefore impact gonadal response.

G-protein-coupled receptor (GPCR) Two variants Type I and II GnRHR Type 1- full length, Type 2 - missense truncation (humans) Resistant to desensitisation (some exceptions) Expressed on gonadotroph cells of anterior pituitary

Glycoproteins with α & β chains α-chains identical in FSH & LH β-chains unique & confer biological actions Rhythm & pulsatility of GnRH Relative rates of gene expression for α/β Slow frequency or low amp GnRH pulse ⇒ ⇧FSHb gene expression Fast frequency GnRH pulse ⇒ ⇧LHb transcription Determines dimerisation of subunits Determines glycosylation Higher frequency GnRH pulse (every 30min) = favours LH secretion Lower frequency/amplitude GnRH pulse (every 90-120min) = favours FSH synthesis and secretion

Premise: ERK1/2 was thought to be the major pathway mediating GnRHR-dependent control of LHb and FSHb- is this the case? Pituitary specific deletion of ERK1/2 to delete ERK1/2 from pituitary gonadotrophs and investigate reproductive consequence in male and female mice.

LH GnRH binds receptor, activates G alpha q/11, activates PLC B, activates DAG, PKC, MEK 1/2, ERK 1/2, EGR FSH GnRH binds receptor, G alpha q/11, PLC B, DAG, PKC, MEK, ERK, difference here is ICER is activate along with CREB

n FEMALES through most of menstrual cycle: Progesterone & low plasma oestrogen  negative feedback Net effect = reduced LH & FSH High sustained (48h) plasma [E2] = enhanced LH & FSH  positive feedback P4 ↓GnRH pulse freq E2 ↓GnRH pulse amplitude Positive feedback on days 12-14 of cycle

Where it would act: Either anterior pituitary or hypothalamus Oestrogen & progesterone receptors on anterior pituitary and hypothalamus Inhibin receptors found only in pituitary How it would work: In anterior pituitary by direct regulation of GnRHR In hypothalamus by directly affecting GnRH neurones or indirectly by changing activity of other neural system that influence GnRH release E2 must only be exerting negative feedback on the anterior pituitary as in rhesus monkeys, the hypothalamus was lesioned and this mechanism had no effect

Positive feedback E2 induces & maintains GnRHR by increasing GnRHR mRNA in pre-ovulatory phase E2 sensitises “self-priming” effect i.e. enhances interaction between GnRH & GnRHR Negative feedback E2 ?? Inhibin?? Progesterone ↓ GnRHR mRNA, also evidence of P4 response element in GnRHR gene

GnRH neurones only express ERβ Need ERα for positive feedback Erα is crucial for reproductive function Erα knock-out mice E2 must act on other afferents that project onto GnRH neurones E2 indirectly stimulates GnRH neurones via other neuronal inputs: Kisspeptin Other hypothalamic neurotransmitters- e.g., GABAnergic neurons