Week 3 Flashcards

Question

What plays a critical role in olfactory bulb morphogenesis and GnRH secretion?

Answer 1

Physiological activation of the prokineticin pathway

Answer 2

Inactivating mutations in prokineticin 2 (Prok2) and its G protein-coupled receptor (GPCR) Recently reported a PROKR2 mutation localised in the first intracellular loop (C1) of PROKR2, R80C in a patient with KS. Additional mutations in the ICL1 of PROKR2, R85C and R85H have also been reported

Answer 3

In GPCRs, the ICL2, ICL3 or C-terminal domain are usually coupled to G proteins

Answer 4

Acts as a G-protein activation region - GnRHR and CCK-AR: ICL1 binds to Gs Is important for cell surface expression - Thromboxane A2 receptor Regulates ER export - A conserved Leu is important for alpha2AR trafficking These intracellular loops are interesting because Extracellular = ligand interaction Production of G proteins etc dependent on overall structure

Answer 5

It has reduced ligand binding and signalling Reduced IP accumulation Reduced ERK activation/ luciferase activity

Answer 6

Exerts a dominant negative effect The R80C PROKR2 mutant targets the WT receptor to degradation The identification of asymptomatic first-degree relatives carrying the R80C PROKR2 mutation suggests that the manifestation of the HH phenotype may depend on additional factors The extent of the dominant negative effect was dependent on the proportion of WT to R80C PROKR2 in vitro Activity of the PROKR2 degradation pathways, differences in the relative expression of the two alleles of the PROKR2 gene, and polymorphisms in regulatory genes may also determine the manifestation of the HH phenotype The presence or extent of the dominant negative effect in vivo may likewise depend on the relative amounts of WT and R80C mutant receptors Binding and signalling issue present Multiple ways that function can be affected

Answer 7

1. DEVELOPMENT AND MIGRATION KAL1/FGF8/FGFR1 PROK2/PROKR2 CHD7 NELF 2. HOMEOSTASIS AND GnRH SECRETION DAX1, PC1, LEP/LEPR, GnRH1, KISS1/KISS1R, FGF8/FGFR1, PROK2/PROKR2, TAC3/TACR3 3. GONADOTROPE STIMULATION DAX1, GNRHR

Answer 8

You dont get the olfactory tract = Anosmia

Answer 9

1. Primordial follicle 2. Primary follicle 3. Secondary follicle 4. Tertiary follicle

Answer 10

The number of follicles declines with age and reproductive senescence occurs when they are completely depleted

Answer 11

Oogonia expand by mitosis during foetal life to provide a stock of egg precursors Eventually all of the oogonia enter meiosis, becoming oocytes Oocytes progress through meiosis I but arrest before completing first division Remain arrested until just before ovulation (>50 years in some mammals) Complete meiosis one, enter 2nd meiosis, become arrested again at MII stage

Answer 12

LEPTOTENE - Duplicated chromosomes start to condense ZYGOTENE - Synapsis begins PROPHASE I PACHYTENE - Synapsis complete; crossing over occurs DIPLOTENE - Synaptonemal complex disappearing; chiasma visible DIAKINESIS - Bivalent ready for metaphase

Answer 13

The growth and development of ovarian follicles from the primordial to ovulatory stages of development

Answer 14

Oocyte Antrum Granulosa Theca

Answer 15

Follicles begin as primordial follicles which consist of one primary oocyte surrounded by a single layer of pre-granulosa cells Development from the primordial follicle stage into a primary follicle is characterised - By an increase in the size of the oocyte - The surrounding of the oocyte by a single layer of cuboidal granulosa cells - The separation of the oocyte from the granulosa cells by a thick layer of material, the zona pellucida

Answer 16

Endothelial cells Granulosa cells Early zona pellucida formation Oocyte

Answer 17

The primary follicle will grow into a secondary follicle The granulosa cells proliferate into multiple layers and at the end of this stage the oocyte is fully grown (~120µm in diameter) Events that characterise this transition are: - The theca layer which eventually will be organised into the theca interna and the theca externa - Vascularisation of the theca Connective tissue cells surrounding the granulosa cells differentiate to form layers of Theca cells

Answer 18

Oocyte Membrana granulosa Basement membrane Theca interna

Answer 19

Produce androgens

Answer 20

Act as substrates for the synthesis of oestrogens by the granulosa cells Granulosa cells secrete: - 17b-oestradiol - Inhibit - Progesterone (small amounts) Despite the presence of the zona pellucida the inner granulosa cells are able to communicate with the oocyte through gap junctions

Answer 21

Following formation of the theca cells, the primary oocyte reaches full size Granulosa cells secrete fluid resulting in the formation of a fluid-filled space, the antrum, a characteristic of antral (tertiary) follicles Other characteristics are: - Development of gap junctions - Differentiation of theca interna cells into steroidogenic cells Antral follicles are responsive to gonadotrophins (mainly FSH) At the beginning of each cycle, a few pre-antral follicles (primary follicles) begin to develop into antral follicles What causes these particular follicles to be selected remains a mystery despite much research! Paracrine action of growth factors eg. EGF, IGFs

Answer 22

Oocyte Antrum Membrana granulosa Basement membrane Theca interna Theca externa

Answer 23

A further selection process occurs whereby a single follicle, termed the dominant follicle, is selected for continued development What causes a single dominant follicle to be chosen is not known Hypophysectomy will prevent complete antral development i.e. for complete antral development need BOTH LH and FSH. The rest of the follicles which had started to enlarge undergo a degenerative process termed atresia

Answer 24

Oocyte Zona pellucida Granulosa cells Follicular cavity Theca

Answer 25

The Graafian follicle enlarges, mainly as a result of its expanding antrum and its growth is dependent on LH as the granulosa cells have now acquired LH receptors Ovulation will occur as a result of a dramatic increase in LH levels

Answer 26

Lengthy process lasting up to several months in cattle and sheep During the preantral stages the oocytes increase dramatically in volume and the granulosa cells multiply to for several layers During these stages thecal cells differentiate from the surrounding stroma and these three cell types (oocyte, GC and TC) form the follicular unit Once germ cells in the foetus stop mitotically dividing, they form associations with a small number of pre-granulosa cells to form primordial follicles. The germ cell enters meiosis, proceeds to the DIPLOTENE stage of prophase I before meiosis is arrested. The primordial follicle is around 35 microns, with an oocyte diameter of 20 to 30 microns. The oocyte is surrounded by a single layer of flattened cells The primary follicle is around 50 microns with an oocyte diameter of around 30 microns. The oocyte is surrounded by a single layer of cubodal GCs The diameter of the secondary follicle is around 100 microns. Oocyte diameter is around 45 microns and several layers of cubodal GCs surround the oocyte. The ZP forms with gap junctions. As the follicle and oocyte grow so the number of gaps junctions between the oocyte and surrounding corona cells increase – largely a function of surface area. Early tertiary follicles (< 1mm) see the formation of the antrum and oocytes are typically between 60 to 80 microns. The oocyte is located within the cumulus oophorus. During these early stages the oocyte is intrinsically incompetent to resume meiosis – due to lack of MPF activity. This will be discussed later, suffice to say at present that at this stage in development the oocyte has not yet synthesised the cell cycle regulatory molecules essential for meiosis progression in sufficient quantities and/or these molecules are not yet positioned correctly within the oocyte. Tertiary follicles (small antral, 1-3 mm), oocyte diameter is between 80 to 110 microns Late tertiary follicles (medium to large follicles, > 3 mm), oocyte diameter > 110 microns Transcriptional activity increases during the secondary follicle stage and remains high until the late tertiary stage. Many of the transcripts necessary to complete the final stages of oocyte maturation and post-fertilisation development are laid down during this period. The resumption of meiosis following ovulation or follicular aspiration induces transcriptional arrest.

Answer 27

BMP: Bone Morphogenetic Protein PTEN: Phosphatase and tensin homolog deleted on chromosome 10 LIF: Leukaemia inhibitory factor GDF-9: Growth differentiation factor-9 NGF: Nerve growth factor KGF: Keratinocyte-growth factor AMH: Anti-mullerian hormone FGF-2: Basic fibroblast growth factor

Answer 28

Entry into meiosis marks the transition of oogonia to oocytes, which occurs between 8 and 13 weeks of gestation, well before the formation of primordial follicles. The oocyte is arrested at the diplotene stage of prophase after proceeding through the leptotene, zygotene and pachytene stages. At the time of ovulation the first meiotic division is completed in which the oocyte finally assumes the haploid stage, albeit still possessing 2c DNA. Then the oocyte proceeds to the second meiotic division and is arrested at metaphase. The second meiotic division is completed at the time of fertilization resulting in 1n chromosomes and 1n with reestablishment of the diploid state. The first primordial follicles begin to appear at around 16 weeks of gestation, and their formation is complete by 6 months after birth in the human ovary. Our current understanding suggests that the earlier stages of follicle growth, from primordial follicle formation to pre-antral–antral stage, are mainly controlled by ligands of several different signaling pathways acting at the paracrine–autocrine level, such as the TGF-β superfamily (scale bars 25 microns). BMP, bone morphogenetic protein; PTEN, tumor suppressor gene (phosphatase and tensin homolog deleted on chromosome 10); LIF, leukaemia inhibitory factor; GDF-9, growth differentiation factor-9; NGF, nerve growth factor; KGF, keratinocyte-growth factor; AMH, anti-Mullerian hormone; FGF-2, basic fibroblast growth factor.

Answer 29

Kit ligand (KL) and basic fibroblast growth factor (bFGF) secreted by pre-granulosa cells and oocyte respectively, have mutual stimulatory effects on oocytes and granulosa cells; they also promote recruitment of theca cells from the surrounding stromal/interstitial cell population. Stromal/interstitial cells and theca cells secrete BMP-4 and BMP-7, which promote follicle activation and survival. GDF-9 and/or BMP-15 secreted by the oocyte of the activated follicle promote granulosa cell proliferation, KL expression and theca formation. Granulosa cells of growing follicles secrete AMH that appears to act as a ‘brake’ on primordial follicle recruitment.

Answer 30

Activation of the PI3K phosphorylates and activates AKT Phosphorylation and activation of FOXO3 Translocation of FOXO3 from the nucleus to the cytoplasm inactivates it, therefore allowing follicle development to progress PTEN is a negative regulator of the PI3K pathway AKT phosphorylates and inactivates TSC, a negative regulator of mTOR As a result, mTOR pathway becomes activated, leading to signals that regulate protein translation and follicle development to progress.

Answer 31

A tumour suppressor gene that plays a key role in maintaining the dormancy of primordial follicles in mammalian ovaries

Answer 32

Termed either oestrus or menstrual cycles Oestrus Cycles - Oestrus is an easily identifiable external marker Menstrual Cycles - Menses is an easily recognised external marker Both oestrus and menstrual cycles consist of a follicular phase and a luteal phase The cycles are dated on the basis of the identifiable external marker i.e. oestrus and menses Hence, day of oestrus and start of menstruation are day 0 in the oestrus and menstrual cycles

Answer 33

Based on changes in the cytology of the endometrium Proliferative phase is oestrogen dominant Secretory phase is progesterone dominant

Answer 34

Follicular phase

Answer 35

Luteal phase

Answer 36

Pool of primordial; quiescent; low atresia Committed: no turning back; low atresia Antrum forms Gonadotrophin-responsive follicles: Development may continue in the absence of LH and FSH BUT gonadotrophins can influence the process; some atresia Gonadotrophin-dependent: Become atretic if FSH falls below 1 ng/ml; high atresia Ovulatory follicles: granulosa cells have LH receptors and can survive if FSH falls below 1ng/ml OVULATION IN THE PRESENCE OF AN LH SURGE OR ATRESIA AFTER ABOUT 72HRS

Answer 37

Follicle death

Answer 38

Hypothalamus secretes GnRH to the anterior pituitary. The anterior pituitary secretes FSH to the granulosa cell, producing oestradiol 17-ß which feeds back to the hypothalamus and anterior pituitary. The granulosa cell feeds back inhibin to the FSH to have a negative effect. The anterior pituitary also secretes LH to the theca cells of the ovary which secrete androgens to the granulosa cell , producing oestradiol 17-ß which feeds back to the hypothalamus and anterior pituitary. The granulosa cell feeds back inhibin to the FSH to have a negative effect. THIS IS THE FOLLICULAR PHASE The anterior pituitary also secretes LH to the luteal cell which produces progesterone. This negatively feeds back to the anterior pituitary and hypothalamus THIS IS THE LUTEAL PHASE

Answer 39

Early-mid follicular phase plasma oestradiol (E2) exerts a negative-feedback on gonadotrophin secretion It acts mainly at the hypothalamus Therefore, FSH levels start to fall The inhibitory effects of E2 occur only whilst the plasma E2 concentration is below a certain threshold value In contrast, when the plasma concentrations rise above the threshold value as occurs during the E2 peak in late follicular phase, it acts on the pituitary to stimulate gonadotrophin secretion The high level of oestradiol ultimately gives rise to the surge of LH

Answer 40

The appearance of apex or stigma on ovary wall The LH surge causes a sets changes within the follicle which leads to ovulation i.e. the release of the egg As a consequence, oestradiol production then falls and progesterone production starts to increase The follicle cells that remain within the ovary are transformed through a process called luteinisation into luteal cells

Answer 41

The CL is formed from proliferation and differentiation of granulosa and theca cells of the ruptured follicle The number of CL formed are directly equal to the number of oocytes released In several species including man, two types of luteal cells have been described - Large cells are thought to arise from granulosa cells - Small cells are thought to arise from theca cells CL is the main source of progesterone production during luteal phase to prepare uterus for embryo implantation Progesterone (P4) is essential for the establishment and maintenance of pregnancy

Answer 42

LH binds to RLH (LH receptor) ↓ Adenylate cyclase ↓ Cyclic AMP ↓ Protein Kinases ↓ Phospho-proteins ↓ Protein synthesis ↓ StAR ↓ Cholesterol ↓ P450 scc in the mitochondrion ↓ Pregnenolone ↓ 3ßHSD PROGESTERONE

Week 3 Flashcards

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