Publications by authors named "Robert Viger"

The steroidogenic acute regulatory (STAR) protein is an essential cholesterol transporter that shuttles cholesterol from the outer to the inner mitochondrial membrane in the major steroidogenic endocrine organs. It is a key player in the acute regulation of steroid hormone biosynthesis in response to tropic hormone stimulation. Its discovery 30 years ago sparked immediate interest in understanding how STAR action is controlled.

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Leydig cells produce hormones required for the development and maintenance of sex characteristics and fertility in males. MEF2 transcription factors are important regulators of Leydig cell gene expression and steroidogenesis. ERK5 is an atypical member of the MAP kinase family that modulates transcription factor activity, either by direct phosphorylation or by acting as a transcriptional coactivator.

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Background: Most of the resources that support the early development of the embryo are stored in the oocyte. Clearing of maternal resources and activation of the embryonic genome to produce its own mRNA transcripts marks the maternal-to-embryo transition. Dependence on stored mRNA can last from a few hours to several days, depending on animal species.

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In Brief: RNA granules travel through the cumulus cell network of transzonal projections which is associated with oocyte developmental competence, and RNA packaging involves RNA-binding proteins of the Fragile X protein family.

Abstract: The determinants of oocyte developmental competence have puzzled scientists for decades. It is known that follicular conditions can nurture the production of a high-quality oocyte, but the underlying mechanisms remain unknown.

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In the testis, Leydig cells produce steroid hormones that are needed to masculinize typical genetic males during fetal development and to initiate and maintain spermatogenesis at puberty and adulthood, respectively. Steroidogenesis is initiated by the transfer of cholesterol from the outer to the inner mitochondrial membrane through the action of steroidogenic acute regulatory protein (STAR). Given its importance for the steroidogenic process, the regulation of gene expression has been the subject of numerous studies.

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Background: Leydig cells produce testosterone and insulin-like 3, two hormones essential for male sex differentiation and reproductive function. The orphan nuclear receptor, chicken ovalbumin upstream promoter transcription factor type II (COUP-TFII), and the zinc finger factor GATA4 are two transcription factors involved in Leydig cell differentiation, gene expression, and function.

Objectives: Several Leydig cell gene promoters contain binding motifs for both GATA factors and nuclear receptors.

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Defining how genes get turned on and off in a correct spatiotemporal manner is integral to our understanding of the development, differentiation, and function of different cell types in both health and disease. Testis development and subsequent male sex differentiation of the XY fetus are well-orchestrated processes that require an intricate network of cell-cell communication and hormonal signals that must be properly interpreted at the genomic level. Transcription factors are at the forefront for translating these signals into a coordinated genomic response.

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Cell differentiation and acquisition of specialized functions are inherent steps in events that lead to normal tissue development and function. These processes require accurate temporal, tissue, and cell-specific activation or repression of gene transcription. This is achieved by complex interactions between transcription factors that form a unique combinatorial code in each specialized cell type and in response to different physiological signals.

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To gain further insight into chromatin-mediated regulation of mammalian sex determination, we analyzed the role of the CHARGE syndrome-associated proteins FAM172A and CHD7. This study is based on our prior discoveries that a subset of corresponding mutant mice display complete male-to-female sex reversal, and that both of these proteins regulate co-transcriptional alternative splicing in neural crest cells. Here, we report that FAM172A and CHD7 are present in the developing gonads when sex determination normally occurs in mice.

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In males, Leydig cells are the main producers of testosterone and insulin-like 3 (INSL3), two hormones essential for sex differentiation and reproductive functions. Chicken ovalbumin upstream promoter-transcription factors I (COUP-TFI/NR2F1) and COUP-TFII (NR2F2) belong to the steroid/thyroid hormone nuclear receptor superfamily of transcription factors. In the testis, COUP-TFII is expressed and plays a role in the differentiation of cells committed to give rise to fully functional steroidogenic adult Leydig cells.

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Geographically, East Asia had the highest liver cancer burden in 2017. Besides this, liver cancer-related deaths were high in Japan, accounting for 3.90% of total deaths.

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PRDM (PRDI-BF1 (positive regulatory domain I-binding factor 1) and RIZ1 (retinoblastoma protein-interacting zinc finger gene 1) homologous domain-containing) transcription factors are a group of proteins that have a significant impact on organ development. In our study, we assessed the role of in neurogenesis and the mechanisms regulating its expression. We found that mRNA expression was induced during neurogenesis and that gene knockout caused premature neuronal differentiation of the P19 cells and enhanced the growth of non-neuronal cells.

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The nuclear receptor chicken ovalbumin upstream promoter-transcription factor type II (COUP-TFII)/NR2F2 is expressed in adult Leydig cells, and conditional deletion of the / gene impedes their differentiation. Steroid production is also reduced in COUP-TFII-depleted Leydig cells, supporting an additional role in steroidogenesis for this transcription factor. COUP-TFII action in Leydig cells remains to be fully characterized.

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GATA4 is an essential transcriptional regulator required for gonadal development, differentiation, and function. In the developing testis, proposed GATA4-regulated genes include steroidogenic factor 1 (Nr5a1), SRY-related HMG box 9 (Sox9), and anti-Müllerian hormone (Amh). Although some of these genes have been validated as genuine GATA4 targets, it remains unclear whether GATA4 is a direct regulator of endogenous Amh transcription.

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Notch2 and Notch3 and genes of the Notch signaling network are dynamically expressed in developing follicles, where they are essential for granulosa cell proliferation and meiotic maturation. Notch receptors, ligands, and downstream effector genes are also expressed in testicular Leydig cells, predicting a potential role in regulating steroidogenesis. In this study, we sought to determine if Notch signaling in small follicles regulates the proliferation response of granulosa cells to FSH and represses the up-regulation steroidogenic gene expression that occurs in response to FSH as the follicle grows.

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GATA4 is an essential transcription factor required for the initiation of genital ridge formation, for normal testicular and ovarian differentiation at the time of sex determination, and for male and female fertility in adulthood. In spite of its crucial roles, the genes and/or gene networks that are ultimately regulated by GATA4 in gonadal tissues remain to be fully understood. This is particularly true for the steroidogenic lineages such as Leydig cells of the testis where many in vitro (promoter) studies have provided good circumstantial evidence that GATA4 is a key regulator of Leydig cell gene expression and steroidogenesis, but formal proof is still lacking.

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Transcription factor GATA4 is required for the development and function of the mammalian gonads. We first reported that the GATA4 gene in both human and rodents is expressed as two major alternative transcripts that differ solely in their first untranslated exon (exon 1a vs. exon 1b).

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Background: The SRY/Sry gene is expressed in pre-Sertoli cells of the male genital ridge and functions as the mammalian testis determining factor (TDF). In addition, expression of SRY/Sry outside the genital ridge has been reported, including preimplantation embryos, although the functional significance of this is not well understood.

Results: Using Cre-mediated lineage studies and transgenic reporter mouse models, we now show that promoter sequences of human, pig and mouse SRY drive robust reporter gene expression in epiblast cells of peri-implantation embryos between embryonic day (E) 4.

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GATA4 is an essential transcription factor required for the development and function of multiple tissues, including a major role in gonadogenesis. Despite its crucial role, the molecular mechanisms that regulate Gata4 expression in vivo remain poorly understood. We recently found that the Gata4 gene is expressed as multiple transcripts with distinct 5' origins.

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Steroid hormone biosynthesis requires the steroidogenic acute regulatory protein (STAR). STAR is part of a protein complex that transports cholesterol through the mitochondrial membrane where steroidogenesis begins. Several transcription factors participate to direct the proper spatiotemporal and hormonal regulation of the Star gene in Leydig cells.

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Sertoli cells are the primary structural component of the fetal testis cords and postnatal seminiferous tubules. Live imaging technologies facilitate the visualization of cell morphologies and behaviors through developmental processes. A transgenic mouse line was generated using a fragment of the rat Gata4 gene to direct the expression of a dual-color fluorescent protein reporter in fetal and adult Sertoli cells.

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Background: GATA4 is an essential transcription factor required for the development and function of multiple organs. Despite this important role, our knowledge of how the GATA4 gene is regulated remains limited. To better understand this regulation, we characterized the 5' region of the mouse, rat, and human GATA4 genes.

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The corpus luteum (CL) is the major site of progesterone (P4) production during the luteal phase of the estrous cycle in cattle. To better understand the molecular mechanisms underlying P4 production, we compared the mRNA and protein expression profiles of key components of the steroidogenic pathway (StAR, CYP11A, and 3beta-HSD) during the bovine CL luteal phase with that of several transcription factors (NR5A1, NR5A2, GATA4, GATA6) known for their roles in the control of steroidogenic gene expression. In the bovine CL, StAR, CYP11A, and 3beta-HSD mRNA and protein levels remained constant at the mid and late luteal phases but markedly declined at the regressed luteal stage.

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GATA transcription factors are crucial regulators of cell-specific gene expression in many tissues including the gonads. Although clinical cases of reproductive dysfunction have yet to be formally linked to GATA gene mutations, they have begun to be reported in other systems. Heterozygous GATA4 mutations have been associated with cases of congenital heart defects.

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Background: In mammals, sex determination is genetically controlled. The SRY gene, located on Y chromosome, functions as the dominant genetic switch for testis development. The SRY gene is specifically expressed in a subpopulation of somatic cells (pre-Sertoli cells) of the developing urogenital ridge for a brief period during gonadal differentiation.

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