Hormonal control of folliculogenesis
Hormonal control of folliculogenesis
Hormonal control of folliculogenesis
Hormonal control of folliculogenesis
BY PROF G M WANI PhD,DVMGermay),DAAD,ISGAPU Fellow,EU acdemic partner-Germany)
At menstruation in women the follicular Artesia is already completed. All developing follicles die down, only one pre-ovulatory follicle remains. The process of apoptosis kills or destroys all other follicles with their oocyte within. The causes of Artesia are unknown, but FSH helps to prevents it.
Follicle development resembles in bovine, humans and equines. Bovines are more similar to human than the equines because of their cycle length and poly estrus behavior {Baerwald, 2009} Follicular development is reported to be in waves. These waves are preceded by the changes in hormonal status i.e. estrogen, progesterone ratio and FSH and L H balances. Selection of a dominant follicle may occur in each wave.
The estradiol, inhibin A, and IGF-II act enables the dominant follicle to grow in a decreasing FSH and increasing LH environment .The subordinate follicles undergo Artesia and death. The use of ultrasonography has helped in study [Ginther et al, 2004] The transition from m ovarian reserve to growing follicles is a continuous process in women. . Response of follicle to FSH Cow Ina 14 day old calf antral follicle were reported (Evans, 1994).
Prenatal follicles are non receptive to the FSH but antral follicle do respond (Adashi, 1997). In women the primordial follicle are recruited and destines to develop in a sequential manner throughout the reproductive life.[Baird,1987] The recruitment of the antral follicles is made both at early and late lacteal phases of the cycle.[McGee and Hsueh,2000]The recruitment of the 2-5 mm follicles is continuous process after puberty.[Gougeon,1979]A theory proposes these follicles are recruited in response to the rise in GnRH and FSH once the corpus lutuem regresses[Hodgen,1982]The follicular phase follicles are 2mm in diameter. Their growth was confusing under the influences of ESTROGEN, PROGESTERONE, FSH AND LH [BAIRD ET AL, 1975] These concepts have changed.
Some updates published as reviewed. [WANI AND WANI 2009, 2010] In bovines and equines the ovulatory follicles have been seen during proestrus, oestrus saw final maturation and ovulation, Corpus lustrum develops during met oestrus and diestrum when CL is functional and secretes progesterone. The oestrus cycle of cows is of 21 days, consisting of 4 days follicular phase and rest as luteal phase, mare has a 7 days follicular phase and long luteal phase. Women have a 14 days follicular phase and are almost half of the whole cycle of 28 days. The circulating FSH declines, estradiol increases. The inhibinA,IGF-II help the follicle who survives to grow as dominant follicle.
Thus one can say a declining FSH and increasing LH hormonal balance helped the follicle to grow and be a dominant one .The other follicles called as subordinate follicle undergo atresia Pre-ovulatory follicle It has been reported that the pre-ovulatory follicle may take a long duration to be formed or survive. They have been seen for 175 days(women) and 160 days in cattle(Geugeon,1986)It takes 42 days for a secondary follicle to reach an ovulatory follicle(Baerwald,2009) Deviation in the ovulatory wave occurs, on average, 4 days after emergence of the largest follicle at 13 mm in mares and at 6 mm in women (Ginther et al.2004), compared to 3 days after emergence of the largest follicle at 4 mm in cattle (Ginther et al., 1997).The dominant follicle maintains a constant growth rate throughout the deviation process, while the subordinate follicles exhibit a reduction in growth rates (Gastal et al., 1997; Ginther et al., 2001a). Follicle-stimulating hormone (FSH), a pituitary glycoprotein hormone, is an integral component of the endocrine axis that regulates gonad function and fertility. To transmit its signal, FSH must bind to its receptor (FSHR) located on granulose cells of the ovary.
THE GONADOTROPIN HORMONES
The gonadotropin-releasing hormone from the hypothalamus, binds receptors on pituitary gonadotrophs and induces the synthesis and secretion of LH and FSH. By binding to their receptors they transmit signals to the gonads. These are neuronal signals from the hypothalamus to the gonads and feedback signals returned to the hypothalamus and pituitary. The receptors for FSH(FSHR) and LH ( LHR) reside on the surface of somatic cells in the gonads and are members of the Rhodopsin receptor family of G protein-coupled receptors (GPCRs), but unlike the other members, LHR and FSHR have extended NH2-terminal extracellular domains with numerous leucine-rich repeats . FSH binding induces adenylyl cyclase, followed by induction of cAMP, protein kinase activation, and protein phosphorylation. FSH binding is also associated with increased intracellular calcium, activation of mitogen-activated protein kinase, and stimulation of inositol triphosphate (Plant,2008,young,1995)
FSHR EXPRESSION
. The granulosa cells being the predominant expressing cell types for FSHR.First found in female embryonic Day 20 . These initial transcripts are incomplete and represent only the extracellular portion of the receptor, with full-length mRNA expressed several days later. In the rodent ovary, Fshr expression coincides with primary follicle formation and follicular development through the pre antral stage, with initial full-length transcripts and hormone binding observed shortly after birth (around Postnatal Day 3) and continuing to increase through Postnatal Day 21 In the ovary,
FSHR is regulated directly by a combination of transcriptional and posttranscriptional mechanisms induced by FSH and activin and indirectly by follistatin through its influence on activin.More details can be seen in the webste www.ncbi.nlm.nih.gov/query/acc.cgi?acc=GSE THE FSHR GENE 1. The FSHR gene has leucine-rich motif, an attribute ascribed to glycoprotein hormone receptor For more details (Hermann and Heckert,2005)
In summary, the evidence to date shows that sequences directing FSHR/Fshr expression lie far from the start of transcription in a regulatory environment without defined boundaries, which complicates their detection using standard molecular approaches. Computational genomics has helped narrow the search, but limitations resulting from false positives and undetected sequences caution its use without additional methods to substantiate the data
. Fortunately, many technologies have adapted to the influx of sequence data by developing high-throughput and genome wide strategies. Two such strategies offer considerable promise for regulatory element identification and for the FSHR/Fshr transcriptional mechanism being within reach. Both strategies reveal chromatin signatures featured in regulatory sequences: One identifies sequences bound to modified histones linked to transcriptional activity by ChIP, and the other identifies open regions of chromatin, similar to DNase I hypersensitivity, by formaldehyde-associated identification of regulatory elements.
. Implementation of such strategies together with comparative genomics will significantly enhance the probability of relevant sequence identification and the mechanistic understanding of the regulatory landscape. When combined with high-throughput strategies, such as DNase-ChIP, high-density tiling arrays and next generation sequencing, to canvass the genome without the bias of conservation, additional insight is likely regarding mechanisms that employ no conserved regulatory elements and possible contributions to species-specific regulatory features [ Gibbs et al,2004.Havlak,et al,2004Hiller,et al,2004,,Giresi et al,2007,wu et al 2006,Roh et al,2007.McGaughey,et al,2009)Many workers screened regulatory elements published in genomics(Chenet al,2008,Crawford et al,2006,)The evolutionarily conserved in vertebrate,insect,worm and yeast have been discribed,(Weinstock et al,2005)
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