Regulation of gene expression in the bovine blastocyst by colony-stimulating factor 2 is disrupted by CRISPR/Cas9-mediated deletion of CSF2RA.

Colony-stimulating factor 2 (CSF2) functions in the reproductive tract to modulate the function of the preimplantation embryo. The ß subunit of the CSF2 receptor (CSF2RB) is not expressed in the embryo, and signal transduction is therefore different than for myeloid cells where the receptor is composed of α (CSF2RA) and ß subunits. Here, we produced embryos in which exons 5 and 6 of CSF2RA were disrupted using the CRISPR/Cas 9 system to test whether CSF2RA signaling was essential for actions of CSF2 in the bovine embryo. Wild-type and CSF2RA knockout embryos were treated with 10 ng/mL CSF2 or vehicle at day 5 of development. Blastocysts were harvested at day 8 to determine transcript abundance of 90 genes by real-time polymerase chain reaction (PCR). Responses in female blastocysts were examined separately from male blastocysts because actions of CSF2 are sex-dependent. For wild-type embryos, CSF2 altered expression of 10 genes in females and 20 in males. Only three genes were affected by CSF2 in a similar manner for both sexes. Disruption of CSF2RA prevented the effect of CSF2 on expression for 9 of 10 CSF2-regulated genes in females and 19 of 20 genes in males. The results confirm the importance of CSF2RA for regulation of gene expression by CSF2 in the blastocyst.

Importance of prostate androgen-regulated mucin-like protein 1 in development of the bovine blastocyst.

BACKGROUND: Prostate androgen-regulated mucin-like protein 1 (PARM1) is a pro-proliferative and anti-apoptotic glycoprotein involved in the endoplasmic reticulum (ER) stress response. A single nucleotide polymorphism in the coding region of PARM1 has been associated with competence of bovine embryos to develop to the blastocyst stage. Here we tested the importance of PARM1 for development by evaluating consequences of reducing PARM1 mRNA abundance on embryonic development and differentiation, gene expression and resistance to ER stress. RESULTS: Knockdown of PARM1 using an anti-PARM1 GapmeR did not affect competence of embryos to develop into blastocysts but decreased the number of trophectoderm (TE) cells in the blastocyst and tended to increase the number of cells in the blastocyst inner cell mass (ICM). Treatment of embryos with anti-PARM1 GapmeR affected expression of 4 and 3 of 90 genes evaluated at the compact-morula and blastocyst stage of development at days 5.5 and 7.5 after fertilization, respectively. In morulae, treatment increased expression of DAB2, INADL, and STAT3 and decreased expression of CCR2. At the blastocyst stage, knockdown of PARM1 increased expression of PECAM and TEAD4 and decreased expression of CCR7. The potential role of PARM1 in ER stress response was determined by evaluating effects of knockdown of PARM1 on development of embryos after exposure to heat shock or tunicamycin and on expression of ATF6, DDIT3 and EIF2AK3 at the compact morula and blastocyst stages. Both heat shock and tunicamycin reduced the percent of embryos becoming a blastocyst but response was unaffected by PARM1 knockdown. Similarly, there was no effect of knockdown on steady-state amounts of ATF6, DDIT3 or EIF2AK3. CONCLUSION: PARM1 participates in formation of TE and ICM cells in early embryonic development but there is no evidence for the role of PARM1 in the ER stress response.

Effects of sex on response of the bovine preimplantation embryo to insulin-like growth factor 1, activin A, and WNT7A.

BACKGROUND: Alterations in maternal environment can sometimes affect embryonic development in a sexually-dimorphic manner. The objective was to determine whether preimplantation bovine embryos respond to three maternally-derived cell signaling molecules in a sex-dependent manner. RESULTS: Actions of three embryokines known to increase competence of bovine embryos to develop to the blastocyst stage, insulin-like growth factor 1 (IGF1), activin A, and WNT member 7A (WNT7A), were evaluated for actions on embryos produced in vitro with X- or Y- sorted semen from the same bull. Each embryokine was tested in embryos produced by in vitro fertilization of groups of oocytes with either pooled sperm from two bulls or with sperm from individual bulls. Embryos were treated with IGF1, activin A, or WNT7A on day 5 of culture. All three embryokines increased the proportion of cleaved zygotes that developed to the blastocyst stage and the effect was similar for female and male embryos. As an additional test of sexual dimorphism, effects of IGF1 on blastocyst expression of a total of 127 genes were determined by RT-qPCR using the Fluidigm Delta Gene assay. Expression of 18 genes was affected by sex, expression of 4 genes was affected by IGF1 and expression of 3 genes was affected by the IGF1 by sex interaction. CONCLUSION: Sex did not alter how IGF1, activin A or WNT7A altered developmental competence to the blastocyst stage. Thus, sex-dependent differences in regulation of developmental competence of embryos by maternal regulatory signals is not a general phenomenon. The fact that sex altered how IGF1 regulates gene expression is indicative that there could be sexual dimorphism in embryokine regulation of some aspects of embryonic function other than developmental potential to become a blastocyst.

Role of yes-associated protein 1, angiomotin, and mitogen-activated kinase kinase 1/2 in development of the bovine blastocyst.

The morula-stage embryo is transformed into a blastocyst composed of epiblast, hypoblast, and trophectoderm (TE) through mechanisms that, in the mouse, involve the Hippo signaling and mitogen-activated kinase (MAPK) pathways. Using the cow as an additional model, we tested the hypotheses that TE and hypoblast differentiation were regulated by the Hippo pathway regulators, yes-associated protein 1 (YAP1) and angiomotin (AMOT), and MAPK kinase 1/2 (MAPK1/2). The presence of YAP1 and CDX2 in the nucleus and cytoplasm of MII oocytes and embryos was evaluated by immunofluorescence labeling. For both molecules, localization changed from cytoplasmic to nuclear as development advanced. Inhibition of YAP1 activity, either by verteporfin or a YAP1 targeting GapmeR, reduced the percent of zygotes that became blastocysts, the proportion of blastocysts that hatched and numbers of CDX2+ cells in blastocysts. Moreover, the YAP1-targeting GapmeR altered expression of 15 of 91 genes examined in the day 7.5 blastocyst. Treatment of embryos with an AMOT targeting GapmeR did not affect blastocyst development or hatching but altered expression of 16 of 91 genes examined at day 7.5 and reduced the number of CDX2+ nuclei and YAP1+ nuclei in blastocysts at day 8.5 of development. Inhibition of MAPK1/2 with PD0325901 did not affect blastocyst development but increased the number of epiblast cells. Results indicate a role for YAP1 and AMOT in function of TE in the bovine blastocyst. YAP1 can also affect function of the epiblast and hypoblast, and MAPK signaling is important for inner cell mass differentiation by reducing epiblast numbers.

Single-cell gene expression of the bovine blastocyst.

The first two differentiation events in the embryo result in three cell types - epiblast, trophectoderm (TE) and hypoblast. The purpose here was to identify molecular markers for each cell type in the bovine and evaluate the differences in gene expression among individual cells of each lineage. The cDNA from 67 individual cells of dissociated blastocysts was used to determine transcript abundance for 93 genes implicated as cell lineage markers in other species or potentially involved in developmental processes. Clustering analysis indicated that the cells belonged to two major populations (clades A and B) with two subpopulations of clade A and four of clade B. Use of lineage-specific markers from other species indicated that the two subpopulations of clade A represented epiblast and hypoblast respectively while the four subpopulations of clade B were TE. Among the genes upregulated in epiblast were AJAP1, DNMT3A, FGF4, H2AFZ, KDM2B, NANOG, POU5F1, SAV1 and SLIT2 Genes overexpressed in hypoblast included ALPL, FGFR2, FN1, GATA6, GJA1, HDAC1, MBNL3, PDGFRA and SOX17, while genes overexpressed in all four TE populations were ACTA2, CDX2, CYP11A1, GATA2, GATA3, IFNT, KRT8, RAC1 and SFN The subpopulations of TE varied among each other for multiple genes including the prototypical TE marker IFNT. New markers for each cell type in the bovine blastocyst were identified. Results also indicate heterogeneity in gene expression among TE cells. Further studies are needed to confirm whether subpopulations of TE cells represent different stages in the development of a committed TE phenotype.

The bovine embryo hatches from the zona pellucida through either the embryonic or abembryonic pole.

PURPOSE: Implantation of the mammalian embryo in the uterus is preceded by escape from the zona pellucida. In some species, hatching from the zona occurs preferentially from one or the other poles of the embryo. The situation for the bovine embryo, in which hatching precedes attachment to the uterus by more than a week, is unclear. The purpose was to describe whether hatching of the bovine embryo from the zona pellucida occurs preferentially from the embryonic or abembryonic pole. METHODS: Bovine blastocysts undergoing hatching were examined by light microscopy (n = 84) and epifluorescence imaging using antibodies for markers of epiblast, hypoblast, and trophectoderm (TE) (n = 26). The location of hatching was classified as being at the embryonic pole, if hatching occurred ipsilateral to the inner cell mass (ICM), or abembryonic, if hatching occurred contralateral to the ICM. RESULTS: A total of 55% of blastocysts exited the zona pellucida through an opening at the embryonic pole. In these cases, 68% of the cells emerging through the zona pellucida were derived from the ICM. The remainder of blastocysts hatched from an opening either contralateral or to the side of the ICM. In these cases, 87% of hatched cells were TE. CONCLUSION: For the bovine embryo, there is nearly equal probability of hatching from the embryonic or abembryonic poles. Given that the surface area of the zona pellucida in contact with the TE overlying the ICM is less than for the remainder of the blastocyst, there is some preference for hatching through the embryonic pole. Thus, the bovine embryo is distinct from the mouse and human, where hatching occurs preferentially at the abembryonic pole.

Role of chemokine (C-C motif) ligand 24 in spatial arrangement of the inner cell mass of the bovine embryo.

The process of spatial rearrangement of cells of the inner cell mass (ICM) that are destined to become hypoblast is not well understood. The observation that the chemokine (C-C motif) ligand 24 (CCL24) and several other genes involved in chemokine signaling are expressed more in the ICM than in the trophectoderm of the bovine embryo resulted in the hypothesis that CCL24 participates in spatial organization of the ICM. Temporally, expression of CCL24 in the bovine embryo occurs coincidently with blastocyst formation: transcript abundance was low until the late morula stage, peaked in the blastocyst at Day 7 of development and declined by Day 9. Treatment of embryos with two separate antagonists of C-C motif chemokine receptor 3 (the prototypical receptor for CCL24) decreased the percent of GATA6+ cells (hypoblast precursors) that were located in the outside of the ICM. Similarly, injection of zygotes with a CCL24-specific morpholino decreased the percent of GATA6+ cells in the outside of the ICM. In conclusion, CCL24 assists in spatial arrangement of the ICM in the bovine embryo. This experiment points to new functions of chemokine signaling in the bovine embryo and is consistent with the idea that cell migration is involved in the spatial organization of hypoblast cells in the blastocyst.

Colony-stimulating factor 2 acts from days 5 to 7 of development to modify programming of the bovine conceptus at day 86 of gestation†.

Colony-stimulating factor 2 (CSF2) is an embryokine that improves competence of the embryo to establish pregnancy and which may participate in developmental programming. We tested whether culture of bovine embryos with CSF2 alters fetal development and alleviates abnormalities associated with in vitro production (IVP) of embryos. Pregnancies were established by artificial insemination (AI), transfer of an IVP embryo (IVP), or transfer of an IVP embryo treated with 10 ng/ml CSF2 from day 5 to 7 of development (CSF2). Pregnancies were produced using X-sorted semen. Female singleton conceptuses were collected on day 86 of gestation. There were few morphological differences between groups, although IVP and CSF2 fetuses were heavier than AI fetuses. Bicarbonate concentration in allantoic fluid was lower for IVP than for AI or CSF2. Expression of 92 genes in liver, placenta, and muscle was determined. The general pattern for liver and placenta was for IVP to alter expression and for CSF2 to sometimes reverse this effect. For muscle, CSF2 affected gene expression but did not generally reverse effects of IVP. Levels of methylation for each of the three tissues at 12 loci in the promoter of insulin-like growth factor 2 (IGF2) and five in the promoter of growth factor receptor bound protein 10 were unaffected by treatment except for CSF2 effects on two CpG for IGF2 in placenta and muscle. In conclusion, CSF2 can act as a developmental programming agent but alone is not able to abolish the adverse effects of IVP on fetal characteristics.

Determination of allelic expression of h19 in pre- and peri-implantation mouse embryos.

H19 is a maternally expressed, imprinted, noncoding RNA with tumor-suppressor activity. During mouse preimplantation development, H19 is primarily expressed in the trophectoderm cells. The purpose of this project was to determine allelic expression of H19 in pre- and peri-implantation mouse embryos. We were further interested in determining if loss of imprinted H19 expression during blastocyst development occurred as a result of superovulation and/or culture. Our last goal was to ascertain if differential H19 allelic expression occurred between the inner cell mass (ICM)-containing half and the primary trophoblast giant cell (PTGC)-containing half of the embryo. C57BL/6J((Cast-7))xC57BL/6J F1 embryos were collected from the uterus at 84, 96, and 108 h following natural ovulation or superovulation. In vitro-cultured F1 embryos were harvested from the oviduct at the 2-cell stage and cultured in KSOM + aa supplemented with amino acids or Whitten media and collected at the above-mentioned times. Allele-specific H19 expression in single embryos was determined by qRT-PCR followed by fluorescence resonance electron transfer or RT-PCR followed by restriction fragment length polymorphism and polyacrylamide gel electrophoresis (RFLP-PAGE). Peri-implantation embryos were microdissected into two sections, one containing the ICM and the other containing the PTGC. TaqMan probes for Dek, Pou5f1, Itga7, H19, and Igf2 were used to ascertain gene expression enrichment in each section. Allele-specific H19 expression in embryo sections was determined by RFLP-PAGE. We found that as embryos advance through preimplantation development they start expressing H19 in a biallelic manner and this phenomenon was observed in the cultured and the in vivo-developed embryos. The PTGC-containing half of the embryo had greater expression of H19 when compared to the ICM-containing half of the embryo, as determined by qRT-PCR. In conclusion, loss of imprinting of H19 occurs in the PTGC-containing section of peri-implantation mouse embryos. We speculate that this is part of a physiologic event at the time of implantation in the mouse.