Understanding Of Ovarian Function Research Articles

Prohibition of hormones in animal reproduction: what to expect and what to do?

As our understanding of ovarian function in cattle has improved, our ability to control it has also increased. The development of Fixed-Time Artificial Insemination (FTAI) protocols at the end of the 20th century has increased exponentially the number of animals inseminated over the last 20 years. The main reasons for this growth were the possibility of obtaining acceptable pregnancy rates without heat detection and, above all, the induction of cyclicity in suckled cows in postpartum anestrus and prepubertal heifers at the beginning of the breeding season. Most FTAI treatments in South America have been based on the use of progesterone (P4) releasing devices and estradiol to synchronize both follicular wave emergence and ovulation, with pregnancy rates ranging from 40 to 60%. These protocols are implemented on a regular basis, allowing producers access to high-quality genetics, and increasing the overall pregnancy rates during the breeding season. In addition, it provided the professionals involved in these programs with a new source of income and the diversification of their practices into activities other than their usual clinical work. Many of these practices are now apparently at risk from restrictions on the use of estradiol by the European Union (EU) and other countries. However, the development of alternative protocols based on GnRH, with P4 devices and eCG and other new products that are not in the market yet will allow us to adapt to the new times that are coming. Logically, the challenge has already been raised and we must learn to use alternative protocols to try to continue increasing the use of this technology in beef and dairy herds. The objective of the present review is to describe the main aspects of banning estradiol in livestock production, the negative impacts on reproductive efficiency, and to present some alternative FTAI protocols for dairy and beef cattle.

Evolución del conocimiento sobre la fisiología ovárica y su contribución a la aplicación de las biotecnologías reproductivas en Sudamérica

As our understanding of ovarian function in cattle has improved, our ability to control it has also increased. Luteal function in cattle has been studied in detail, and prostaglandin F2α has been used for several years for elective induction of luteal regression. More recently, follicular wave dynamics have been studied and protocols have been designed to induce follicular wave emergence and ovulation, and the need to detect oestrus has even been eliminated. The addition of progesterone, estradiol, GnRH and equine chorionic gonadotropin (eCG) releasing devices has provided opportunities for fixed-time AI (IATF) and possibilities for achieving higher pregnancy rates. In embryo transfer programs, these same treatments have eliminated the need to detect oestrus, allowing fixed-time embryo transfer (TETF) and the initiation of superstimulatory treatments regardless of the day of the estrous cycle. Taken together, the new protocols have facilitated the application of assisted reproductive technologies, and this is especially true in South America. Over the past 20 years, the use of AI in South America has increased, due in large part to the use of the IATF. The use of the IATF has been multiplied by more than 10 times in Brazil, with more than 11 million treatments in 2016, which represents 85% of all AI. Similar trends are occurring in Argentina and Uruguay. In vivo embryo production produced by superovulation (DIV) has remained relatively stable over the years, but in vitro embryo production (PIV) has increased dramatically in the last 10 to 15 years, especially in Brazil, where More than 300,000 PIV embryos were produced in 2010. Worldwide, over 990,000 bovine PIV embryos were produced in 2017, of which more than% were produced in South America. The use of assisted reproductive technologies has facilitated the spread of genetic improvements and increased reproductive performance; These practices are spreading to many South American countries.

Evolution of knowledge on ovarian physiology and its contribution to the widespread application of reproductive biotechnologies in South American cattle.

As our understanding of ovarian function in cattle has improved, our ability to control it has also increased. Luteal function in cattle has been studied in detail, and prostaglandin F2α has been used for several years for the elective induction of luteal regression. More recently, follicle wave dynamics has been studied and protocols designed to induce follicular wave emergence and ovulation have reduced, and even eliminated, the need for estrus detection. The addition of progestin-releasing devices, estradiol, GnRH and equine chorionic gonadotropin (eCG) have provided opportunities for fixed-time AI (FTAI) and possibilities for increased pregnancy rates. In embryo transfer programs, these same treatments have eliminated the need for estrus detection, permitting fixed-time embryo transfer and the initiation of superstimulatory treatments without regard to day of the estrous cycle. Collectively, new treatment protocols have facilitated the application of assisted reproductive technologies, and this is especially true in South America. Over the last 20 years, the use of AI in South America has increased, due largely to the use of FTAI. There has been more than a 10-fold increase in the use of FTAI in Brazil with more than 11 million treatments in 2016, representing 85% of all AI. Similar trends are occurring in Argentina and Uruguay. Production of in vivo-derived (IVD) embryos has remained relatively stable over the years, but in vitro embryo production (IVP) has increased dramatically over the past 10 to 15 years, especially in Brazil where more than 300,000 IVP embryos were produced in 2010. World-wide, more than 666,000 bovine IVP embryos were produced in 2016, of which more than 57% were produced in South America. The use of assisted reproductive technologies has facilitated the dissemination of improved genetics and increased reproductive performance; other South American countries are now following suit.

The role of Notch signaling in the mammalian ovary.

The Notch pathway is a contact-dependent, or juxtacrine, signaling system that is conserved in metazoan organisms and is important in many developmental processes. Recent investigations have demonstrated that the Notch pathway is active in both the embryonic and postnatal ovary and plays important roles in events including follicle assembly and growth, meiotic maturation, ovarian vasculogenesis and steroid hormone production. In mice, disruption of the Notch pathway results in ovarian pathologies affecting meiotic spindle assembly, follicle histogenesis, granulosa cell proliferation and survival, corpora luteal function and ovarian neovascularization. These aberrations result in abnormal folliculogenesis and reduced fertility. The knowledge of the cellular interactions facilitated by the Notch pathway is an important area for continuing research, and future studies are expected to enhance our understanding of ovarian function and provide critical insights for improving reproductive health. This review focuses on the expression of Notch pathway components in the ovary, and on the multiple functions of Notch signaling in follicle assembly, maturation and development. We focus on the mouse, where genetic investigations are possible, and relate this information to the human ovary.

ANIMAL MODELS FOR THE STUDY OF HUMAN OVARIAN FUNCTION

The study of ovarian function has been of great interest to scientists and clinicians in the human and veterinary health fields for more than 20 centuries. Initial studies of the ovaries were based on anatomical descriptions post-mortem, followed by histological and endocrinological approaches. The introduction of high-resolution ultrasonography provided a long-awaited tool to image the reproductive tissues in situ in both animals and humans. Critical studies of the characteristics and control of ovarian follicular and luteal dynamics in non-human primates, rodents, and domestic farm animals have involved frequent (i.e. daily or multiple times a day) blood sampling and ultrasonography. Studies of this nature in women are difficult, and often unethical to conduct. Differences in antral folliculogenesis between humans and animals appear to be more in detail rather than in essence, and may reflect differences in intrinsic physiology or merely differences in our ability to detect changes in a given species. In women, the presence of endometrial shedding and symmetric luteal and follicular phases are different from that observed during the estrous cycles of domestic farm animals but despite these differences, general similarities in antral follicular dynamics exist. A continuous pattern of antral follicle development was originally proposed in domestic livestock species; however, the use of frequent serial ultrasonography and simultaneous endocrine profiling in these animal species has resulted in a broad understanding of follicular wave dynamics. Follicular waves have now been described in every species in which this approach has been used, including humans. The relatively large diameters of antral follicles in cows and mares, compared to monkeys, sheep, and rodents provide greater feasibility for characterizing antral follicular dynamics ultrasonographically. Profound similarities in the dynamics of follicle development exist between the menstrual cycle in humans and the estrous cycle in cattle and horses. Despite a proportionately longer luteal phase in cows and mares, the growing phase of the dominant ovulatory follicle (defined as the time period from wave emergence to ovulation) is comparable in the human, cow, and mare. Thus, at present, cows and mares may be the most appropriate models for the study of antral follicular dynamics in women. While the use of animal models has increased our understanding of ovarian function and provides the hypothetical basis for studies in women, differences in vocabulary, culture, and research methodologies between scientists in predominantly human versus animal settings has hampered knowledge translation. These differences represent a systemic impediment to a broad understanding of ovarian function and limits progress and innovation in the development of safer and more efficacious treatments for infertility and contraception.

NR5A1et insuffisance ovarienne primaire

Primary ovarian insufficiency (POI) is characterised by the arrest of normal ovarian function before the age of 40 years and affects 1 % of all women. POI shows familial inheritance suggesting a genetic contribution. NR5A1 is nuclear receptor that regulates the transcription of many genes involved in sexual developmental and reproduction. 18 NR5A1 mutations have been published associated with either anomalies of adrenal or testis development. We have identified NR5A1 mutations associated with POI, including familial cases with affected 46,XY individuals. This demonstrates that NR5A1 plays an important role in ovarian development and function. However several questions remain. What is the incidence of NR5A1 mutations in POI? Is there a genotype/phenotype relationship? Are mutations associated with a progressive loss of reproductive function? Answering these questions will lead to a better understanding of ovarian function and dysfunction and could lead to new therapies for treating POI.

Identification of transcripts involved in meiosis and follicle formation during ovine ovary development

BackgroundThe key steps in germ cell survival during ovarian development are the entry into meiosis of oogonies and the formation of primordial follicles, which then determine the reproductive lifespan of the ovary. In sheep, these steps occur during fetal life, between 55 and 80 days of gestation, respectively. The aim of this study was to identify differentially expressed ovarian genes during prophase I meiosis and early folliculogenesis in sheep.ResultsIn order to elucidate the molecular events associated with early ovarian differentiation, we generated two ovary stage-specific subtracted cDNA libraries using SSH. Large-scale sequencing of these SSH libraries identified 6,080 ESTs representing 2,535 contigs. Clustering and assembly of these ESTs resulted in a total of 2,101 unique sequences depicted in 1,305 singleton (62.11%) and 796 contigs (37.9%) ESTs (clusters). BLASTX evaluation indicated that 99% of the ESTs were homologous to various known genes/proteins in a broad range of organisms, especially ovine, bovine and human species. The remaining 1% which exhibited any homology to known gene sequences was considered as novel. Detailed study of the expression patterns of some of these genes using RT-PCR revealed new promising candidates for ovary differentiation genes in sheep.ConclusionWe showed that the SSH approach was relevant to determining new mammalian genes which might be involved in oogenesis and early follicle development, and enabled the discovery of new potential oocyte and granulosa cell markers for future studies. These genes may have significant implications regarding our understanding of ovarian function in molecular terms, and for the development of innovative strategies to both promote and control fertility.

The importance of comparative physiology: a focus on ovarian biology and the role of animal models.

Abstract The use of animals in research dates back many centuries. Using animals as a model to advance human health is critical, and an important aspect of that is choosing the right animal model. In utilizing animals for research, not only do we advance our understanding of fundamental biology and physiology, but the findings contribute to knowledge of animal disease and welfare issues as well. The following discussion is an overview discussing how studies in animals have advanced our understanding of ovarian function, and the need to continue to develop appropriate animal models to address critical questions. The use of the bat Glossophaga soricina as a model for ovarian biology is noted.

Ovarian follicle development and transgenic mouse models

Ovarian follicle development is a complex process that begins with the establishment of what is thought to be a finite pool of primordial follicles and culminates in either the atretic degradation of the follicle or the release of a mature oocyte for fertilization. This review highlights the many advances made in understanding these events using transgenic mouse models. Specifically, this review describes the ovarian phenotypes of mice with genetic mutations that affect ovarian differentiation, primordial follicle formation, follicular growth, atresia, ovulation and corpus luteum (CL) formation. In addition, this review describes the phenotypes of mice with mutations in a variety of genes, which affect the hormones that regulate folliculogenesis. Because studies using transgenic animals have revealed a variety of reproductive abnormalities that resemble many reproductive disorders in women, it is likely that studies using transgenic mouse models will impact our understanding of ovarian function and fertility in women.

Angiogenesis in normal and neoplastic ovaries

Ovarian physiology is intricately connected to hormonally regulated angiogenic response. Recent advances in the post genomic revolution have significantly impacted our understanding of ovarian function. In an angiogenesis perspective, the ovary offers a unique opportunity to unravel the molecular orchestration of blood vessel development and regression under normal conditions. A majority of ovarian cancers develop from the single layer of epithelium surrounding the ovaries. Angiogenesis is critical for the development of ovarian cancer and its peritoneal dissemination. The present review summarizes recent findings on the angiogenic response in neoplastic ovaries and discusses the prospects of using anti-angiogenic approaches to treat ovarian cancer.

Chlorotic Girls, 1870-1920: A Historical Perspective on Female Adolescence

In light of the current interest in anorexia nervosa, this historical study explores the relationship of culture to age- and gender-specific symptomatologies. Between 1870 and 1920, chlorosis, a form of anemia, was widely reported in female adolescents in the United States. Diagnosis occurred on both the clinical and popular levels, yet neither the etiology nor the symptoms were precisely clear. Treatment generally included rest and large doses of iron salts. In large part, chlorosis was a cultural construction embedded in the context of Victorian medicine and family life. Physicians expected to see chlorosis in adolescent girls in the process of sexual maturation; girls learned to have the disease from family, friends, the popular press, and their doctors. Changes in diet and nutrition after 1900, coupled with increased understanding of ovarian function and iron deficiency anemia, provide only a partial explanation of the disease's eventual decline. By 1920, a changed social environment made chlorosis a social liability for girls and their mothers.