48 Different chromatin accessibility in murine male and female inner cell mass

Previous research has shown that embryos conceived by IVF show a sexual dimorphic phenotype and different metabolite expression into adulthood. Interestingly, female embryos have a higher apoptotic rate and are more vulnerable to environmental stressors. Our prior studies have examined DNA methylation changes in male and female embryos; however, limited knowledge is available with regard to chromatin accessibility in male and female embryos. The objective of this study was to assess if genome-wide chromatin accessibility changes occur in the inner cell mass (ICM) of the male v. female mouse embryo. For this experiment we utilised expanded blastocysts (CF-1 females×B6D2F1 males) that were obtained by IVF or flushed out of the uterus (FB, control). We performed IVF using KSOM with amino acids and 5% O2. The ICM were isolated from trophectoderm cells utilising immunosurgery and complement. The chromatin status was assessed using an assay for transposase-accessible chromatin status using a sequencing (ATAC seq) protocol modified from Wu et al. (2016 Nature 524, 652-657, DOI: 10.1038/nature18606). Briefly, cells were lysed and nuclei incubated with the Tn5 transposome and tagmentation buffer (Nextera, Illumina Inc., San Diego, CA, USA). After tagmentation, PCR amplification (15 cycles), mitochondrial depletion, and library purification were performed. The sex of the embryo was determined based on MSY (male sex region on the Y chromosome) and total Y chromosome aligning reads. Samples were then divided into 2 groups, male (n=20) and female (n=25), and sequencing was completed using Illumina HiSEqn 2500 (Illumina Inc.). Sequencing was completed using Illumina HiSEqn 2500. MACS2 (https://github.com/taoliu/MACS/) was used for peak identification from the sequencing results and DESEqn 2 (https://www.r-project.org/) was used for statistical analysis and false discovery rate<0.1 was considered significant. GREAT analysis (http://great.stanford.edu/public/html/) was used to identify the top biological processes. Overall, 17,136 regions were identified as more open in males and 19,460 regions were identified as more open in females. Interestingly, of these identified regions, only 28 were considered significant (25 increased and 3 decreased in males). The majority of these regions were located on chromosome Y and most of the regions that were increased in male correlated with gene Gm10352, a gene with an unknown function. While some pathway changes were expected, like the ones involved in sex determination, male gonadal development, and male sexual characteristics, others included histone demethylation, regulation of chromatin silencing, negative regulation of DNA replication, and antigen processing and presentation of peptide antigen. Our data are the first to analyse genome-wide chromatin accessibility changes in the ICM of male and female mouse embryos. Importantly, these data indicate that chromatin differences are already present in the ICM of male and female embryos. Further analysis will provide insights into epigenetic and sexual dimorphic changes present in embryos.

In vitro culture of mouse embryos reduces differential gene expression between inner cell mass and trophectoderm

Differences in gene expression and imprinting have been reported, comparing in vivo versus in vitro generated preimplantation embryos. Furthermore, mouse studies have shown that placenta development is altered following in vitro culture. However, the molecular mechanisms underlying these findings are unknown. We therefore isolated trophectoderm (TE) and inner cell mass (ICM) cells from in vivo and in vitro fertilization (IVF) embryos and evaluated their transcriptome using microarrays. We found that the transcriptomes of in vitro produced ICM and TE cells showed remarkably few differences compared to ICM and TE cells of in vivo generated embryos. In vitro fertilization embryos showed a reduced number of TE cells compared to in vivo embryos. In addition, TE of IVF embryos showed significant downregulation of solute transporter genes and of genes involved in placenta formation (Eomesodermin, Socs3) or implantation (Hbegf). In summary, IVF and embryo culture significantly affects the transcriptome of ICM and TE cells.

Effect of ICSI on gene expression and development of mouse preimplantation embryos

BACKGROUND

In vitro culture (IVC) and IVF of preimplantation mouse embryos are associated with changes in gene expression. It is however not known whether ICSI has additional effects on the transcriptome of mouse blastocysts.

METHODS

We compared gene expression and development of mouse blastocysts produced by ICSI and cultured in Whitten's medium (ICSI(WM)) or KSOM medium with amino acids (ICSI(KSOMaa)) with control blastocysts flushed out of the uterus on post coital Day 3.5 (in vivo). In addition, we compared gene expression in embryos generated by IVF or ICSI using WM. Global pattern of gene expression was assessed using the Affymetrix 430 2.0 chip.

RESULTS

Blastocysts from ICSI fertilization have a reduction in the number of trophoblastic and inner cell mass cells compared with embryos generated in vivo. Approximately 1000 genes are differentially expressed between ICSI blastocyst and in vivo blastocysts; proliferation, apoptosis and morphogenetic pathways are the most common pathways altered after IVC. Unexpectedly, expression of only 41 genes was significantly different between embryo cultured in suboptimal conditions (WM) or optimal conditions (KSOM(aa)).

CONCLUSIONS

Our results suggest that fertilization by ICSI may play a more important role in shaping the transcriptome of the developing mouse embryo than the culture media used.

Effect of the method of conception and embryo transfer procedure on mid-gestation placenta and fetal development in an IVF mouse model

BACKGROUND

Abnormal placentation is a potential mechanism to explain the increased incidence of low birthweight observed after IVF. This study evaluates, in a mouse model, whether the method of conception and embryo transfer affect placentation and fetal development.

METHODS

IVF blastocysts (CF1 x B6D2F1/J) were cultured in Whitten's medium (IVF(WM), n = 55) or K modified simplex optimized medium with amino acids (IVF(KAA), n = 56). Embryos were transferred to the uteri of pseudo-pregnant recipients. Two control groups were created: unmanipulated embryos produced by natural mating (in vivo group, n = 64) and embryos produced by natural mating that were flushed from uterus and immediately transferred to pseudo-pregnant recipients (flushed blastocysts, FB group, n = 57). At gestation age 12.5 days, implantation sites were collected and fixed; fetuses and placentas were weighed and their developmental stage (DS) evaluated. Placental areas and vascular volume fractions were calculated; parametric statistics were applied as appropriate.

RESULTS

IVF fetuses showed a modest but significant delay in development compared with FB mice (P < 0.05). In addition, IVF conceptuses were consistently smaller than FB (P < 0.05). Importantly, these differences persisted when analyzing fetuses of similar DS. The placenta/fetus ratio was larger in the IVF group (IVF(WM) 0.95; IVF(KAA) = 0.90) than the FB group (0.72) (P < 0.05 for all comparisons). Gross morphology of the placenta and ratio labyrinth/fetal area were equivalent in the IVF and FB groups, as were percentage of fetal blood vessels, maternal blood spaces and trophoblastic components.

CONCLUSIONS

In vitro embryo culture affects fetal and placental development; this could explain the lower birthweight in IVF offspring.

Role of epithelial-mesenchymal interactions in the differentiation and spatial organization of visceral smooth muscle

Uterine mesenchyme from newborn (0-day) rats was grown in association with epithelia from the adult cornea, urinary bladder, oesophagus, mammary gland, 1-day skin, and 1-day uterus. Following 1 month of growth, the differentiation of uterine mesenchyme into actin-positive smooth muscle cells was assessed immunocytochemically with antibodies to smooth muscle actin. Whereas grafts of uterine mesenchyme produced only small amounts of myometrium, all types of epithelia induced extensive myometrial differentiation in the uterine mesenchyme, which indicates that this effect is non-specific. The role of cell-cell interactions in the morphological patterning of smooth muscle layers was assessed by analysing tissue recombinants composed of adult prostatic epithelium (PRE) plus mesenchyme of the urogenital sinus (UGM), or seminal vesicle (SVM), or adult bladder epithelium (BLE) plus UGM or SVM. Prostatic ducts developed in all of these tissue recombinants (UGM + BLE, SVM + BLE, UGM + PRE and SVM + PRE). When UGM was used (UGM + PRE and UGM + BLE recombinants), actin-positive smooth muscle cells became organized into thin sheaths resembling the prostatic pattern. Conversely, when SVM was grown in association with PRE or BLE, the induced prostatic ducts were surrounded by thick layers of smooth muscle cells exhibiting the seminal vesicle pattern of organization. Smooth muscle cells were unorganized in grafts of SVM or UGM alone. These observations suggest that in male urogenital glands the mesenchyme dictates the spatial organization of the smooth muscle layers.(ABSTRACT TRUNCATED AT 250 WORDS)

A morphological study of the epididymides of control and estradiol-treated prepubertal dogs

Treatment of laboratory beagles with 400 micrograms of estradiol benzoate every fourth day from 5 to 20 wk of age severely alters the gross and microscopic morphology of the epididymis. Both stroma and epithelium are affected by estradiol treatment. The peritubular cells of treated animals appear to be fibroblasts separated by broad expanses of collagen, while the control peritubular cells resemble smooth muscle cells separated by small amounts of collagen. The single epithelial cell type present in the treated pup is low columnar and relatively undifferentiated in appearance. These cells appear to be synthetically active based on the accumulation of material within the lumen. The junctions of the epithelial cells of treated animals are occluding, but those of the control are not. The epithelium of control epididymides is composed of columnar principal cells in the caput epididymidis, and principal cells and basal cells in the pseudostratified epithelium of the corpus and cauda epididymidis. The epididymis of the intact, prepubertal dog is responsive to increased estrogen. The presence of estrogen and progesterone receptors (Jones and Connell, 1982) as well as androgen receptors (Younes et al., 1979) suggests that estrogens, progestins, and androgens all may play an essential role in the normal differentiation of the prepubertal epididymis. This is the first description of the ultrastructure of the epididymis of the 20-wk-old dog and the first description of the effect of chronic estrogen treatment on the ultrastructure of the epididymis of the intact prepubertal dog. We propose that the prepubertal dog epididymis is an excellent model system for the study of the hormonal control of epididymal differentiation and development.