Oxygen concentration affects de novo DNA methylation and transcription in in vitro cultured oocytes.

BACKGROUND: Reproductive biology methods rely on in vitro follicle cultures from mature follicles obtained by hormonal stimulation for generating metaphase II oocytes to be fertilised and developed into a healthy embryo. Such techniques are used routinely in both rodent and human species. DNA methylation is a dynamic process that plays a role in epigenetic regulation of gametogenesis and development. In mammalian oocytes, DNA methylation establishment regulates gene expression in the embryos. This regulation is particularly important for a class of genes, imprinted genes, whose expression patterns are crucial for the next generation. The aim of this work was to establish an in vitro culture system for immature mouse oocytes that will allow manipulation of specific factors for a deeper analysis of regulatory mechanisms for establishing transcription regulation-associated methylation patterns. RESULTS: An in vitro culture system was developed from immature mouse oocytes that were grown to germinal vesicles (GV) under two different conditions: normoxia (20% oxygen, 20% O2) and hypoxia (5% oxygen, 5% O2). The cultured oocytes were sorted based on their sizes. Reduced representative bisulphite sequencing (RRBS) and RNA-seq libraries were generated from cultured and compared to in vivo-grown oocytes. In the in vitro cultured oocytes, global and CpG-island (CGI) methylation increased gradually along with oocyte growth, and methylation of the imprinted genes was similar to in vivo-grown oocytes. Transcriptomes of the oocytes grown in normoxia revealed chromatin reorganisation and enriched expression of female reproductive genes, whereas in the 5% O2 condition, transcripts were biased towards cellular stress responses. To further confirm the results, we developed a functional assay based on our model for characterising oocyte methylation using drugs that reduce methylation and transcription. When histone methylation and transcription processes were reduced, DNA methylation at CGIs from gene bodies of grown oocytes presented a lower methylation profile. CONCLUSIONS: Our observations reveal changes in DNA methylation and transcripts between oocytes cultured in vitro with different oxygen concentrations and in vivo-grown murine oocytes. Oocytes grown under 20% O2 had a higher correlation with in vivo oocytes for DNA methylation and transcription demonstrating that higher oxygen concentration is beneficial for the oocyte maturation in ex vivo culture condition. Our results shed light on epigenetic mechanisms for the development of oocytes from an immature to GV oocyte in an in vitro culture model

Identification of the genes regulated by Wnt-4, a critical signal for commitment of the ovary

AbstractThe indifferent mammalian embryonic gonad generates an ovary or testis, but the factors involved are still poorly known. The Wnt-4 signal represents one critical female determinant, since its absence leads to partial female-to-male sex reversal in mouse, but its signalling is as well implicated in the testis development. We used the Wnt-4 deficient mouse as a model to identify candidate gonadogenesis genes, and found that the Notum, Phlda2, Runx-1 and Msx1 genes are typical of the wild-type ovary and the Osr2, Dach2, Pitx2 and Tacr3 genes of the testis. Strikingly, the expression of these latter genes becomes reversed in the Wnt-4 knock-out ovary, suggesting a role in ovarian development. We identified the transcription factor Runx-1 as a Wnt-4 signalling target gene, since it is expressed in the ovary and is reduced upon Wnt-4 knock-out. Consistent with this, introduction of the Wnt-4 signal into early ovary cells ex vivo induces Runx-1 expression, while conversely Wnt-4 expression is down-regulated in the absence of Runx-1. We conclude that the Runx-1 gene can be a Wnt-4 signalling target, and that Runx-1 and Wnt-4 are mutually interdependent in their expression. The changes in gene expression due to the absence of Wnt-4 in gonads reflect the sexually dimorphic role of this signal and its complex gene network in mammalian gonad development

Roles of <em>Wnt4/5a</em> in germ cell differentiation and gonad development &amp; <em>ErbB4</em> in polarity of kidney epithelium

Abstract The embryonic urogenital system generates the metanephric kidneys, the gonads and the adrenal glands, and its development is based on sequential and reciprocal cell and tissue interactions. The mechanisms which regulate urogenital ontogeny are still poorly understood. In this thesis, the roles of Wnt-4 and ErbB4 functions in gonad and kidney development were analysed by using in vivo functional genomic technologies. Wnt-4 is crucial in female development since its absence leads to a partial female to male sex reversal. We found that Wnt-4 mediated the interactions between the somatic and the germ cells and played a role in meiosis which is regulated in part by the secreted signal retinoic acid (RA). Expression of certain meiosis-controlling genes (Stra8, Spo11) was inhibited in the Wnt-4 deficient germ cells, while certain pluripotency genes (Oct4, Fgf9, Sox2 and Dnmt3l) were activated similarly as in the wild-type male gonad. In addition to this, we noted that a gene encoding for a Cyp26b1 enzyme, which degrades RA in the embryonic testis, was ectopically expressed in the Wnt-4 deficient ovary. Microarray analysis was used to identify candidate Wnt-4 target genes by using the Wnt-4 knock-out mouse. Of these genes, Runx-1 may represent a novel signalling target to mediate Wnt-4 activity in the control female development The role of receptor-tyrosine kinase ErbB4 in kidney development was studied by using both in vivo gain and loss of function approaches. In the gain-of-function situation, we found that certain markers for the epithelial tubules and collecting ducts lost their polarized expression pattern. At the same time, the orientation of the cells in the kidney tubules was deregulated and an increase in cell proliferation was noticed. We suggest that the observed defects gave rise to an increase in the tubule diameter and to cyst formation in the kidney cortex. In the loss-of-function mouse, the lack of ErbB4 expression led to a similar phenotype as with the gain of function, and the renal functions of the mutant adult kidneys were compromised. In conclusion, the results point to specific roles for Wnt-4 and ErbB4 in the control of urogenital development. Wnt-4 appears to be crucial in sustaining proper female somatic cell and germ cell differentiation, and maintenance of gonad development during and after the sex determination event, while ErbB4 activity is critical for the regulation of tubular growth in embryonic kidney development.Tiivistelmä Sekä nisäkkään jälkimunuainen, lisämunuainen että sukurauhanen kehittyvät alkion urogenitaalialueen järjestelmästä ja solu- ja kudosvuorovaikutukset ohjaavat elinkehitysprosessia. Tapahtuman molekyylitason mekanismit ovat kuitenkin huonosti tunnettuja. Tässä väitöskirjatyössä tutkittiin Wnt-4 signaalin tehtäviä sukurauhasen ja ErbB4- proteiinin munuaisen kehityksessä. Wnt-4 signaali on keskeinen naisen sukupuolisuuden kehityksessä, koska signaalin puutos aiheuttaa alkion sukupuolen osittaisen kääntymisen naaraasta koiraaksi. Tarkastelimme aluksi sitä, välittääkö Wnt-4 itusolujen ja sukurauhasen somaattisten solujen vuorovaikutuksia ohjaten itusolujen meioosia, jota mm. A-vitamiini säätelee. Havaitsimme, että Wnt-4 geeni puuttuessa tietyt meioosia säätelevät geenit kuten Stra8 ja Spo11 olivat heikentyneet, kun taas solujen monikykyisyyteen liittyvät geenit kuten Oct4, Fgf9, Sox2 ja Dnmt3l aktivoituivat vastaavalla tavalla kuin havaitaan normaalisti koirasalkion kivesaiheessa. Tämän lisäksi havaitsimme, että Cyp26b1-geeni, joka johtaa A-vitamiinin hajoamiseen alkiossa ja estää normaalisti meioosin koirasalkion kivesaiheessa oli aktivoitunut munuaisrauhasaiheessa, jolta puuttuu Wnt-4 aktiivisuus. Tuloksemme osoittavat, että Wnt-4 säätelee osaltaan naarasalkion itusolujen meioosia. Tarkastelimme myös mikrosirututkimusten avulla niitä geenejä, joita Wnt-4 säätelee sukuelinaiheessa. Identifioimme useissa Wnt ja β-catenin signaalireittiin liittyvissä geeneissa muutoksia. Muuntuneet geenit voivat olla Wnt-4 signaalireitin kohdegeenejä. Näistä Runx-1 saattaa olla keskeinen Wnt signaalitien kohdegeeni, joka säätelee merkittävällä tavalla naaraan munarauhasen kehitystä. Väitöskirjan toisessa osassa tarkastelimme ErbB4-reseptorityrosiinikinaasin tehtäviä munuaisen kehityksen säätelyssä. ErbB4-geenin tehtäviä tutkittiin käyttäen hyväksi siirtogeenisiä malliorganismeja, joissa ErbB4-geenin määrä oli joko koholla tai ajastetusti inaktivoitu. ErbB4- geenin kokeellinen yliaktiivisuus muutti spesifisti tekijöitä, jotka säätelevät osaltaan jälkimunuaisen epiteeliputkien solujen orientaatiota ja solun jakautumista. Solujen orientaatiomuutoksen yhteydessä myös solujen jakautuminen häiriintyi. Oletuksemme on, että nämä epiteelikudoksessa tapahtuneet muutokset ovat syy, miksi kohotettu ErbB4-aktiviteetti muuttaa epiteeliputkien paksuutta ja pituutta erityisesti munuaisen pintakerroksissa. Havaitsimme myös, että ErbB4-geenin ajastettu poistaminen munuaisen epiteelikudoksessa johti hyvin samankaltaisiin, mutta vastakkaisiin muutoksiin kuin ErbB4-aktiviteetin kohottaminen. Muutokset johtivat myös muutoksiin munuaisen toiminnassa. Yhteenvetona toteamme, että näillä Wnt-4 ja ErbB4 solusignallointiin liittyvillä molekyyleillä on keskeinen tehtävä alkion munarauhasen ja munuaisen aiheen kehityksen säätelyssä. Wnt-4 ohjaa sekä itusolujen että somaattisten solujen erilaistumista ja samalla sukupuolen määräytymistä ja jatkokehitystä, kun taas ErbB4-signallointireseptorin tehtävä on avainasemassa munuaisen epiteeliputken kasvun säätelyssä

From ovarian development to folliculogenesis:essential networks sustaining the ovarian reserve

Abstract In the last four decades, transgenic and knockout mouse models have helped to understand the mechanisms of mammalian sex determination, germ cell development, and adult gonad functions. We have gained crucial insights into molecular factors and pathways of the cells generating either the supporting gonadal cells or germ cells of both sexes. In this review, we highlighted some of the main gene networks and regulatory mechanisms involved in the plasticity of sex-determining pathways that help to establish a functional ovary that can nurture the follicles to generate a good ovarian reserve, both in quantity and quality. Although this level of plasticity is still found in the fully differentiated gonads, errors like mutations or epigenetic modifications impact ovarian development and, later, folliculogenesis, resulting in infertility. To highlight some adverse reproductive outcomes associated with perturbations at the molecular and cellular levels in human folliculogenesis, two examples, i.e., Polycystic Ovary Syndrome (PCOS) and Premature Ovarian Insufficiency (POI), were selected and briefly discussed in this review

Deciphering the minimal quantity of mouse primary cells to undergo nephrogenesis ex vivo

Abstract Background: Tissue organoids derived from primary cells have high potential for studying organ development and diseases in numerous organs. They recreate the morphological structure and mimic the functions of given organ while being compact in size, easy to produce, and suitable for use in various experimental setups. Results: In this study we established the number of cells that form mouse kidney rudiments at E11.5, and generated renal organoids of various sizes from the mouse primary cells of the metanephric mesenchyme (MM). We investigated the ability of renal organoids to undergo nephrogenesis upon Wnt/ β-catenin pathway—mediated tubule induction with a GSK-3 inhibitor (BIO) or by initiation through the ureteric bud (UB). We found that 5000 cells of MM cells are necessary to successfully form renal organoids with well-structured nephrons as judged by fluorescent microscopy, transmission electron microscopy (TEM), and quantitative Polymerase Chain Reaction (qPCR). These mouse organoids also recapitulated renal secretion function in the proximal tubules. Conclusions: We show that a significant decrease of cells used to generate renal mouse organoids in a dissociation/re-aggregation assay, does not interfere with development, and goes toward 3Rs. This enables generation of more experimental samples with one mouse litter, limiting the number of animals used for studies

Induced Pluripotent Stem Cells as a Possible Approach for Exploring the Pathophysiology of Polycystic Ovary Syndrome (PCOS).

Funder: University of Helsinki including Helsinki University Central HospitalPolycystic ovary syndrome (PCOS) is the most prevalent endocrine condition among women with pleiotropic sequelae possessing reproductive, metabolic, and psychological characteristics. Although the exact origin of PCOS is elusive, it is known to be a complex multigenic disorder with a genetic, epigenetic, and environmental background. However, the pathogenesis of PCOS, and the role of genetic variants in increasing the risk of the condition, are still unknown due to the lack of an appropriate study model. Since the debut of induced pluripotent stem cell (iPSC) technology, the ability of reprogrammed somatic cells to self-renew and their potential for multidirectional differentiation have made them excellent tools to study different disease mechanisms. Recently, researchers have succeeded in establishing human in vitro PCOS disease models utilizing iPSC lines from heterogeneous PCOS patient groups (iPSCPCOS). The current review sets out to summarize, for the first time, our current knowledge of the implications and challenges of iPSC technology in comprehending PCOS pathogenesis and tissue-specific disease mechanisms. Additionally, we suggest that the analysis of polygenic risk prediction based on genome-wide association studies (GWAS) could, theoretically, be utilized when creating iPSC lines as an additional research tool to identify women who are genetically susceptible to PCOS. Taken together, iPSCPCOS may provide a new paradigm for the exploration of PCOS tissue-specific disease mechanisms

Induced Pluripotent Stem Cells as a Possible Approach for Exploring the Pathophysiology of Polycystic Ovary Syndrome (PCOS)

Polycystic ovary syndrome (PCOS) is the most prevalent endocrine condition among women with pleiotropic sequelae possessing reproductive, metabolic, and psychological characteristics. Although the exact origin of PCOS is elusive, it is known to be a complex multigenic disorder with a genetic, epigenetic, and environmental background. However, the pathogenesis of PCOS, and the role of genetic variants in increasing the risk of the condition, are still unknown due to the lack of an appropriate study model. Since the debut of induced pluripotent stem cell (iPSC) technology, the ability of reprogrammed somatic cells to self-renew and their potential for multidirectional differentiation have made them excellent tools to study different disease mechanisms. Recently, researchers have succeeded in establishing human in vitro PCOS disease models utilizing iPSC lines from heterogeneous PCOS patient groups (iPSCPCOS). The current review sets out to summarize, for the first time, our current knowledge of the implications and challenges of iPSC technology in comprehending PCOS pathogenesis and tissue-specific disease mechanisms. Additionally, we suggest that the analysis of polygenic risk prediction based on genome-wide association studies (GWAS) could, theoretically, be utilized when creating iPSC lines as an additional research tool to identify women who are genetically susceptible to PCOS. Taken together, iPSCPCOS may provide a new paradigm for the exploration of PCOS tissue-specific disease mechanisms.Peer reviewe