Hormonal regulation of microRNA expression in the ovary

The ovary is a dynamic organ that is charged with the responsibility of producing a viable gamete so that the circle of life can be reproduced for future generations. The ovary is also responsible for producing, secreting, and maintaining the proper hormone milieu of estrogens and progesterone for maintenance of pregnancy and the overall fitness of a woman's health. Understanding the mechanisms that regulate the interplay between hormone action and biological function is critical for furthering our knowledge of fertility and reproductive health. For decades, research has been conducted on understanding the transcriptional regulation of ovarian gene expression and how this relates to reproductive function. Recently, attention has turned to alternative forms of gene regulation, including post-transcriptional gene regulation. One mechanism of post-transcriptional gene regulation is the expression and function of microRNA (miRNA). These highly conserved, short, non-coding RNA molecules primarily silence gene expression by directly interfering with protein translation or causing the degradation of messenger RNA. The focus of these studies was to first determine if miRNA are necessary for female fertility. Conditional deletion of Dicer, a key processing enzyme in miRNA biogenesis, in ovarian granulosa cells, the oviduct, and uterus, led to a drastic decrease in ovulation rate and complete infertility in female mice. To further investigate the role of miRNA in ovulation, we next investigated miRNA-212 and -132. While these two co-transcribed miRNA were highly induced by the luteinizing hormone surge immediately prior to ovulation, they did not appear to have an effect on female fertility in the mouse. In a second series of studies, we analyzed the regulation of miRNA by hormones in two in vivo models. We found that miRNA expression was altered in theca cells from women suffering from polycystic ovarian syndrome (PCOS) and that expression of miRNA was altered in the fetal ovaries of sheep exposed to an excess of prenatal androgens. Taken together, these studies provide evidence that miRNA are crucial for female fertility and ovarian function and that hormones influence the expression of ovarian miRNA in diseased states. These studies support the need for further study to understand the mechanisms through which these post-transcriptional regulators affect ovarian function, so that we can potentially use them as a therapeutic target to help overcome infertility and/or disease

The role of peroxisome proliferator activated-receptor gamma in ovarian function

The transcription factor, peroxisome proliferator activated-receptor γ (PPARγ), regulates many processes critical for normal ovarian function. The role of PPARγ in the ovary was investigated by determining its expression throughout the bovine estrous cycle, and luteal tissue was cultured with agonists and an antagonist of PPARγ to determine its impact on progesterone production. Protein, but not mRNA for PPARγ, was lower in regressing compared to functional luteal tissue. Treatment with a PPARγ agonist decreased progesterone secretion from late phase luteal tissue. These findings indicate that PPARγ may play a role in luteal formation/function, and alter progesterone production during specific stages of the ovarian cycle. To facilitate further study of how PPARγ impacts ovarian biology, transgenic mice were developed with the gene for PPARγ specifically disrupted in granulosa cells. Knowing what genes are regulated by PPARγ in the ovary will aid in understanding the mechanisms behind the cyclic pattern of gene expression driving normal ovarian function

Humanized H19/Igf2 locus reveals diverged imprinting mechanism between mouse and human and reflects Silver–Russell syndrome phenotypes

Genomic imprinting is essential for mammalian development. Curiously, elements that regulate genomic imprinting, the imprinting control regions (ICRs), often diverge across species. To understand whether the diverged ICR sequence plays a species-specific role at the H19/insulin-like growth factor 2 (Igf2) imprinted locus, we generated a mouse in which the human ICR (hIC1) sequence replaced the endogenous mouse ICR. We show that the imprinting mechanism has partially diverged between mouse and human, depending on the parental origin of the hIC1 in mouse. We also suggest that our mouse model is optimal for studying the imprinting disorders Beckwith–Wiedemann syndrome when hIC1 is maternally transmitted, and Silver–Russell syndrome when hIC1 is paternally transmitted

Characterization of BRD4 during mammalian post-meiotic sperm development

During spermiogenesis, the post-meiotic phase of mammalian spermatogenesis, transcription is progressively repressed as nuclei of haploid spermatids are compacted through a dramatic chromatin reorganization involving hyper-acetylation and replacement of most histones with protamines. Although BRDT functions in transcription and histone removal in spermatids, it is unknown whether other BET family proteins play a role. Immunofluorescence of spermatogenic cells revealed BRD4 in a ring around the nuclei of spermatids containing hyper-acetylated histones. The ring lies directly adjacent to the acroplaxome, the cytoskeletal base of the acrosome, previously linked to chromatin reorganization. The BRD4 ring does not form in acrosomal mutant mice. ChIP sequencing in spermatids revealed enrichment of BRD4 and acetylated histones at the promoters of active genes. BRD4 and BRDT show distinct and synergistic binding patterns, with a pronounced enrichment of BRD4 at spermatogenesis-specific genes. Direct association of BRD4 with acetylated H4 decreases in late spermatids as acetylated histones are removed from the condensing nucleus in a wave following the progressing acrosome. These data provide evidence for a prominent transcriptional role of BRD4 and suggest a possible removal mechanism for chromatin components from the genome via the progressing acrosome as transcription is repressed in response to chromatin condensation during spermiogenesis

Developmental programming of the female neuroendocrine system by steroids

Developmental programming refers to processes that occur during early life that may have long-term consequences, modulating adult health and disease. Complex diseases, such as diabetes, cancer and cardiovascular disease, have a high prevalence in different populations, are multifactorial, and may have a strong environmental component. The environment interacts with organisms, affecting their behaviour, morphology and physiology. This interaction may induce permanent or long-term changes, and organisms may be more susceptible to environmental factors during certain developmental stages, such as the prenatal and early postnatal periods. Several factors have been identified as responsible for inducing the reprogramming of various reproductive and nonreproductive tissues. Among them, both natural and synthetic steroids, such as endocrine disruptors, are known to have either detrimental or positive effects on organisms depending on the dose of exposure, stage of development and biological sexual background. The present review focuses on the action of steroids and endocrine disruptors as agents involved in developmental programming and on their modulation and effects on female neuroendocrine functions.Fil: Abruzzese, Giselle Adriana. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Houssay. Centro de Estudios Farmacológicos y Botánicos. Universidad de Buenos Aires. Facultad de Medicina. Centro de Estudios Farmacológicos y Botánicos; ArgentinaFil: Crisosto, Nicolás. Facultad de Medicina de la Universidad de Chile; Chile. Clinica Las Condes; ChileFil: De Grava Kempinas, Wilma. Universidade Estadual Paulista Julio de Mesquita Filho; BrasilFil: Sotomayor Zárate, Ramón. Universidad de Valparaiso; Chil

Dicer1 Depletion in Male Germ Cells Leads to Infertility Due to Cumulative Meiotic and Spermiogenic Defects

Background: Spermatogenesis is a complex biological process that requires a highly specialized control of gene expression. In the past decade, small non-coding RNAs have emerged as critical regulators of gene expression both at the transcriptional and post-transcriptional level. DICER1, an RNAse III endonuclease, is essential for the biogenesis of several classes of small RNAs, including microRNAs (miRNAs) and endogenous small interfering RNAs (endo-siRNAs), but is also critical for the degradation of toxic transposable elements. In this study, we investigated to which extent DICER1 is required for germ cell development and the progress of spermatogenesis in mice.Principal Findings: We show that the selective ablation of Dicer1 at the early onset of male germ cell development leads to infertility, due to multiple cumulative defects at the meiotic and post-meiotic stages culminating with the absence of functional spermatozoa. Alterations were observed in the first spermatogenic wave and include delayed progression of spermatocytes to prophase I and increased apoptosis, resulting in a reduced number of round spermatids. The transition from round to mature spermatozoa was also severely affected, since the few spermatozoa formed in mutant animals were immobile and misshapen, exhibiting morphological defects of the head and flagellum. We also found evidence that the expression of transposable elements of the SINE family is up-regulated in Dicer1-depleted spermatocytes.Conclusions/Significance: Our findings indicate that DICER1 is dispensable for spermatogonial stem cell renewal and mitotic proliferation, but is required for germ cell differentiation through the meiotic and haploid phases of spermatogenesis

Long-Term Effects of the Periconception Period on Embryo Epigenetic Profile and Phenotype: The Role of Stress and How This Effect Is Mediated

Stress represents an unavoidable aspect of human life, and pathologies associated with dysregulation of stress mechanisms - particularly psychiatric disorders - represent a significant global health problem. While it has long been observed that levels of stress experienced in the periconception period may greatly affect the offspring's risk of psychiatric disorders, the mechanisms underlying these associations are not yet comprehensively understood. In order to address this question, this chapter will take a 'top-down' approach, by first defining stress and associated concepts, before exploring the mechanistic basis of the stress response in the form of the hypothalamic-pituitary-adrenal (HPA) axis, and how dysregulation of the HPA axis can impede our mental and physical health, primarily via imbalances in glucocorticoids (GCs) and their corresponding receptors (GRs) in the brain. The current extent of knowledge pertaining to the impact of stress on developmental programming and epigenetic inheritance is then extensively discussed, including the role of chromatin remodelling associated with specific HPA axis-related genes and the possible role of regulatory RNAs as messengers of environmental stress both in the intrauterine environment and across the germ line. Furthering our understanding of the role of stress on embryonic development is crucial if we are to increase our predictive power of disease risk and devise-effective treatments and intervention strategies

The sperm factor: paternal impact beyond genes

The fact that sperm carry more than the paternal DNA has only been discovered just over a decade ago. With this discovery, the idea that the paternal condition may have direct implications for the fitness of the offspring had to be revisited. While this idea is still highly debated, empirical evidence for paternal effects is accumulating. Male condition not only affects male fertility but also offspring early development and performance later in life. Several factors have been identified as possible carriers of non-genetic information, but we still know little about their origin and function and even less about their causation. I consider four possible non-mutually exclusive adaptive and non-adaptive explanations for the existence of paternal effects in an evolutionary context. In addition, I provide a brief overview of the main non-genetic components found in sperm including DNA methylation, chromatin modifications, RNAs and proteins. I discuss their putative functions and present currently available examples for their role in transferring non-genetic information from the father to the offspring. Finally, I identify some of the most important open questions and present possible future research avenues