1. Advanced Reproduction Physiology (Part 2) Isfahan University of Technology College of Agriculture, Department of Animal Science Prepared by: A. Riasi http://riasi.iut.ac.ir

2. Oogenesis & Folliculogenesis

3. Overview 1: ovary, 2: tertiary follicle, 3: proper ovarian ligament, 4: fallopian tube, 5: ovarian artery and vein

4. Overview

7.  The ovaries have two distinct functions: Producing the sex steroids and protein hormones  Prepare the vagina and fallopian tubes to assist in fertilization  Prepare the lining of uterus to accept and implant a zygote  Maintain hormonal support for the fetus before placenta capacity  Act on diverse target organs Overview Ovogenesis and folliculogenesis  Maintain and nurture the resident oocyte  Mature the oocyte and release it at the right time

8.  Primordial germ cells migrate from the yolk sac  The primordial germ cells proliferate by mitosis to form primary oocytes: In cattle, the first meiotic prophase in days 75-80 The first meiotic division is not completed befor ovulation The biology of oogenesis

9.  In contrast the male, the female cannot manufacture new oogonia It must function with continuously declining number of primary oocytes. The biology of oogenesis

10.  The first stage of development of the ovarian follicle parallels the prophase of the oocyte.  As an oocyte enters meiosis, it induces a single layer of spindle cells to surround it completely. Cytoplasmic processes from these cells attach to the plasma membrane of the oocyte. Folliculogenesis

11.  In the next phase, the spindle-shaped cells become cuboidal and granulosa cells and a primary follicle is formed.  Then secondary follicle is created.  After that the zona pellucida is formed. Folliculogenesis

13.  During the initial deposition of zona pellucida material some changes occur in oocyte: Formation of cortical granules within the oocyte cytoplasm Onset of oocyte RNA synthesis Gonadotrophin responsiveness Folliculogenesis

14.  Primordial, primary and secondary follicles appear in the fetal ovary on Days 90, 140 and 210, respectively (Russe, 1983).  The second stage of follicular development is take place during in postnatal and in puberty. Folliculogenesis

15.  Follicular growth in prepubertal heifers occurs in waves.  Each wave is preceded by a peak in serum FSH concentrations (Fortune, 2004).  There is a marked but transient increase in blood concentrations of both LH and FSH. Folliculogenesis

16.  From 30-80 days before the first ovulation, the LH pulses frequency result: Increases in follicle diameter Increase in serum estradiol concentrations Enhancing antral follicle development Folliculogenesis

17.  The transition to the tertiary follicle includes: Development of the theca interna and externa Formation of basal lamina Formation of cumulus cells Formation of a fluid-filled antral cavity Folliculogenesis

18.  The fluid in the antrum contains different chemicals: Mucopolysachrides Plasma proteins Electrolytes Glycosoaminoglycans Proteoglycans Gonadal steroid hormones FSH, Inhibin and other factors Folliculogenesis

21.  The final stage of follicular development occurs only in the postpubertal reproductive ovary.  Some event in third stage: The granulosa cells spread apart The cumulus oophorus loosens The follicle generally ruptures, releasing the oocyte with adherent cumulus oophorus At this time the initial meiotic division complete Folliculogenesis

22.  Follicles develop in waves.  Emergence of a new follicular wave is preceded by a rise in FSH.  Suppression of FSH prevents further growth of 3-5 mm follicles. Follicular waves

23.  The FSH surge peaks, on average, when the largest follicle is about 5 mm.  Rather than selection of a dominant follicle, selection involves an action against the other follicles in the wave (Ginther et al, 2003). Follicular waves

24.  A subordinate follicle remains viable for at least 1 day after deviation starts  Administration of FSH when a dominant follicle is present does not consistently hasten emergence of the next wave Follicular waves

25.  With decreasing serum FSH concentrations, follicles begin to undergo changes: Reduced production of estrogens Reduced levels of higher molecular weight (MW) inhibins Increased amounts of lower MW insulin-like growth factor (IGF)-binding proteins Culminating in granulosa cell apoptosis Follicular waves

26.  FSH stimulates the production of estradiol, activin-A and inhibin-A (Glister et al, 2001).  These FSH-stimulated factors have intrafollicular roles in deviation.  Both estradiol and inhibin act alone (as well as synergistically) to suppress blood FSH concentrations. Follicular waves

27.  The estradiol secretion by dominant follicle increase the expression of genes in granulosa cells for: Aromatase 3-beta-HSD Receptors for FSH and LH Follicular waves

29. Selection Dominance Ovulation Follicular Size Day After Ovulation 91621 Recruitment Atresia Progesterone Follicular waves

31.  The IGF system is involved in cell growth and differentiation and consists of: IGF-1 IGF-2 IGF receptors A family of binding proteins (IGFBPs) IGFBP proteases Follicular waves

32.  It appears that pregnancy-associated-plasma protein-A (PAPP-A) is the earliest change detectable in the future dominant follicle.  PAPP-A is a protease and increase intrafollicular IGF- I concentrations. Follicular waves

33.  Increased IGF-I acts together with FSH to increase estradiol synthesis.  It is noteworthy that estradiol stimulates the production of IGF-1 and IGF-1 stimulates the production of estradiol. Follicular waves

34.  In the early estrogenic follicle some changes occur for receptors: The mRNAs for the FSH receptor and aromatase are elevated within the granulosa layer. Theca cells have increased abundances of LH receptor and 17α-hydroxylase. Follicular waves

35. Two cell, two-gonadotropin theory of ovarian steroidogenesis Follicular waves

36.  Dynamic changes are evident within the inhibin family: In estrogen-active follicle the large molecular weight inhibins (i.e., >160 kDa) are elevated. In estrogen-inactive follicles the smaller inhibins (32 to 34 kDa) are increased. Follicular waves

37.  FSH secretion by pituitary gland will reduce by: The increased secretions of estradiol The increased secretion of large MW inhibin  Lack of FSH prevents further growth of subordinate follicles, which are also nonestrogenic due to low concentrations of free IGF-I. Follicular waves

38.  Once the dominant follicle reaches 10 mm its granulosa cells begin to express LH receptors.  Continued growth and dominance of the dominant follicle beyond10 mm appears to be dependent upon LH secretion. Follicular waves

39. Ovarian follicular and corpus luteum development correlated with endocrine changes during the bovine estrous cycle. E2 = Estradiol; IGFBP-4 and -5 = insulin- like growth factor binding proteins 4 and 5; OvF = ovulatory follicle. * * * * * * * * * + + + + + + Follicular waves

40.  Dominant follicles continue to grow for a few days after selection.  If there is an LH surge the dominant follicle continues to grow and the oocyte within undergoes: Final maturation Culminating in follicle rupture Ovulation Follicular waves

41.  Final maturation includes: Expansion of the cumulus cover Disruption of the contact between the corona radiata cells and the oocyte membrane Perivitelline space formation Increase lipid content in oocyte cytoplasm Decrease golgi compartment in oocyte cytoplasm Follicular waves

42.  Final maturation includes: The cortical granules are aligned just inside the oocyte membrane The chromosomes condense and progress through the final stages of meiosis I and arrest at metaphase of meiosis II Follicular waves

43.  The peak and average plasma concentrations of FSH and inhibin A are lower in the two non-ovulatory waves than a three-wave cycle Follicular waves

44.  Higher fertility in three-wave cycles could be due to: A shorter interval for development of the ovulatory follicle (Townson et al, 2002). Delayed regression of the corpus luteum. Follicular waves

45. Ovulation Follicular Size Day After Ovulation 91621 FSH Sensitive Pool Recruitment Selection Dominance Atresia Progesterone

46.  Ovulation takes place about 10-14 hours after the end of oestrus.  The gonadotropin surge is important for ovulation: Increase progesterone production Increase estrogen production Increase prostaglandins (PGE2 & PGF2α) Ovulation

47.  In its early stages of growth the corpus haemorrhagicum is difficult to palpate.  The corpus luteum (CL) is palpable at about five days post ovulation. Corpus luteum formation

48.  It frequently has a distinct crown: About ½ cm in diameter About ½ cm high  The corpus luteum enlarges progressively to two to three cm by day-8 or 9 and has a liver like consistency. Corpus luteum formation

49.  Actually the CL is made up two cell groups: The large luteal cells, which originated from granulosa cells. The small luteal cells which originated from theca cells.  The luteal cells are steroidogenic and secrete progesterone. Corpus luteum formation

50.  Progesterone has the following functions during pregnancy: It prevents the cow from coming on heat. The function of the hormone oxytocin is blocked. It regulates the changes in the mucous membranes in the uterus. It plays a role in the formation of udder tissue. Corpus luteum formation

51. Some research papers associated to this lecture 1.Beg, M. A. et al. 2002. Follicle Selection in Cattle: Dynamics of follicular fluid factors during development of follicle dominance. Biology of Reproduction. 66: 120–126. 2.Bisinotto, R. S. Et al. 2010. Follicular wave of the ovulatory follicle and not cyclic status influences fertility of dairy cows. J. Dairy Sci. 93 :3578– 3587. 3.Rýfat, M. et al. 2005. Evaluation of the corpus luteum size throughout the cycle by ultrasonography and progesterone assay in cows. Turk. J. Vet. Anim. Sci. 29: 1311-1316.