Lecture 3 Flashcards
(27 cards)
GnRH
10 amino acids
acts at GnRH receptor – a GPCR that signals through Gαq
stimulates transcription FSH & LH
stimulates FSH & LH release
two modes of GnRH release:
pulses & surge
FSH & LH secretion from Anterior Pituitary
dimeric glycoproteins - a and B subunit
subunits identical; B-subunits confer hormone specificity
FSH domination
early follicular phase
stimulated by slow GnRH pulse frequencies
released through constitutive pathway
LH domination
late follicular phase
stimulated by fast GnRH pulse frequencies
packaged in electron-dense granules in association with storage protein secretogranin II
FSH/ LH release
movement of granules to cell membrane abutting a capillary - polarisation
GnRH -> Gaq -> PLC -> Ca2+ -> LH release
GnRH -> Gaq -> PLC -> PKA -> MAPK -> transcription -> FSH/ LH release
3 regulatory programmes for follicle development driven by
FSH
LH
Follicle (somatic cells and oocytes)
Follicular development
Primordial germ cells migrate from yolk sac to fetal ovary
Mitosis but incomplete cytokinesis: interconnected cells (germ cell cysts / nests)
oocytes enter meiosis (arrested in PROphase of meiosis I) breakdown of intracellular bridges enclosure of oocytes
primordial follicles (≈1x106 at birth)
oogonia stem cells
Isolated cells expressing DDX4 from human adult ovary using an anti-DDX4 antibody
DDX4 – DEAD box polypeptide 4; evolutionary conserved germ-cell specific RNA helicase
isolated cells mitotically active
labelled isolated cells with GFP
Primordial follicle
Primary oocyte (MI prophase) Granulosa cells (flat)
Primary follicle
Primary oocyte (MI prophase) Granulosa cells (cuboidal) ZP
Secondary follicle
Primary oocyte (MI prophase) Granulosa cells (multiple layers) Zona pellucida Theca – interna & externa
activation is Gn-independent
Oocyte-secreted factors (OSF)
- members of TGFβ superfamily
GDF 9 (Growth Differentiation Factor 9)
BMP15 (Bone Morphogenic Protein 15)
Granulosa cell
kit ligand – promotes follicle development
AMH (Anti-Mullerian Hormone) – may restrain development
Tertiary follicle (antral follicles)
Primary oocyte (MI prophase) Zona pellucida Theca – interna & externa Granulosa cells – mural & cumulus Antral cavity: absent in FSHβ k/o mice Sex steroids
Early follicular phase
there are no sex steroids being produced
no negative feedback to the hypothalamus Slow pulses so AP produces FSH, some LH
FSH produces secondary follicles which can produce tertiary
Sex steroid synthesis
acetate -> cholesterol -> pregnenolone
- > progesterone / 17-hydroxypregnenolone
- > DHEA -> androstenedione
androstenedione
aromatase -> estrone
testosterone
aromatase -> 17-estradiol
Thecal cell
LH binds to LHR Thecal cell releases androgens androgens diffuse into granulosa cell FSH binds to FSHR granulosa cells have aromatase which binds to androgens to produce 17-estradiol
FSH & LH Receptors
GPCRs
present on somatic cells in ovarian follicles (initially LH Receptor is only expressed on the thecal cells, but as it matures it then is found on the granulosa cells
generally coupled to Gs
activates adenylate cyclase
cAMP activates protein kinase A (PKA) - phosphorylation - Arg-Arg-X-Ser/Thr-X motif in proteins
e.g. enzymes in steroidogenesis
CREB -> nucleus
OSF
Oocyte influences granulosa (cumulus) cell via OSF
bind to cell surface Ser/Thr kinases activate Smad signalling molecules
translocate to nucleus
act as transcription factors
regulate granulosa cell
proliferation
differentiation
extracellular matrix production if ovulated so can stick to oviduct to move along
estradiol production
metabolism
Cumulus cells influence oocyte
nutrients
meiotic arrest
