The birth and adult development of 'Dolly' the sheep, the first mammal produced by the transfer of a terminally differentiated cell nucleus into an egg, provided unequivocal evidence of nuclear equivalence among somatic cells. This ground-breaking experiment challenged a long-standing dogma of irreversible cellular differentiation that prevailed for over a century and enabled the development of methodologies for reversal of differentiation of somatic cells, also known as nuclear reprogramming. Thanks to this new paradigm, novel alternatives for regenerative medicine in humans, improved animal breeding in domestic animals and approaches to species conservation through reproductive methodologies have emerged. Combined with the incorporation of new tools for genetic modification, these novel techniques promise to (i) transform and accelerate our understanding of genetic diseases and the development of targeted therapies through creation of tailored animal models, (ii) provide safe animal cells, tissues and organs for xenotransplantation, (iii) contribute to the preservation of endangered species, and (iv) improve global food security whilst reducing the environmental impact of animal production. This review discusses recent advances that build on the conceptual legacy of nuclear transfer and – when combined with gene editing – will have transformative potential for medicine, biodiversity and sustainable agriculture. We conclude that the potential of these technologies depends on further fundamental and translational research directed at improving the efficiency and safety of these methods.

This review summarizes new knowledge on expression of genes and provides insights into approaches for study of conceptus–endometrial interactions in ruminants with emphasis on the peri-implantation stage of pregnancy. Conceptus–endometrial interactions in ruminants are complex and involve carefully orchestrated temporal and spatial alterations in gene expression regulated by hormones from the ovary and conceptus. Progesterone is the hormone of pregnancy and acts on the uterus to stimulate blastocyst survival, growth, and development. Inadequate progesterone levels or a delayed rise in progesterone is associated with pregnancy loss. The mononuclear trophectoderm cells of the elongating blastocyst synthesize and secrete interferon-τ (IFNT), the pregnancy recognition signal. Trophoblast giant binucleate cells begin to differentiate and produce hormones including chorionic somatomammotropin 1 (CSH1 or placental lactogen). A number of genes, induced or stimulated by progesterone, IFNT, and/or CSH1 in a cell-specific manner, are implicated in trophectoderm adhesion to the endometrial luminal epithelium and regulation of conceptus growth and differentiation. Transcriptional profiling experiments are beginning to unravel the complex dynamics of conceptus–endometrial interactions in cattle and sheep. Future experiments should incorporate physiological models of pregnancy loss and be complemented by metabolomic studies of uterine lumen contents to more completely define factors required for blastocyst survival, growth, and implantation. Both reduction and holistic approaches will be important to understand the multifactorial phenomenon of recurrent pregnancy loss and provide a basis for new strategies to improve pregnancy outcome and reproductive efficiency in cattle and other domestic animals.

The epigenetic status of a donor nucleus has an important effect on the developmental potential of embryos produced by somatic cell nuclear transfer (SCNT). In this study, we transferred cultured rabbit cumulus cells (RCC) and fetal fibroblasts (RFF) from genetically marked rabbits (Alicia/Basilea) into metaphase II oocytes and analyzed the levels of histone H3-lysine 9-lysine 14 acetylation (acH3K9/14) in donor cells and cloned embryos. We also assessed the correlation between the histone acetylation status of donor cells and cloned embryos and their developmental potential. To test whether alteration of the histone acetylation status affects development of cloned embryos, we treated donor cells with sodium butyrate (NaBu), a histone deacetylase inhibitor. Further, we tried to improve cloning efficiency by chimeric complementation of cloned embryos with blastomeres from in vivo fertilized or parthenogenetic embryos. The levels of acH3K9/14 were higher in RCCs than in RFFs (P<0.05). Although the type of donor cells did not affect development to blastocyst, after transfer into recipients, RCC cloned embryos induced a higher initial pregnancy rate as compared to RFF cloned embryos (40 vs 20%). However, almost all pregnancies with either type of cloned embryos were lost by the middle of gestation and only one fully developed, live RCC-derived rabbit was obtained. Treatment of RFFs with NaBu significantly increased the level of acH3K9/14 and the proportion of nuclear transfer embryos developing to blastocyst (49 vs 33% with non-treated RFF, P<0.05). The distribution of acH3K9/14 in either group of cloned embryos did not resemble that in in vivo fertilized embryos suggesting that reprogramming of this epigenetic mark is aberrant in cloned rabbit embryos and cannot be corrected by treatment of donor cells with NaBu. Aggregation of embryos cloned from NaBu-treated RFFs with blastomeres from in vivo derived embryos improved development to blastocyst, but no cloned offspring were obtained. Two live cloned rabbits were produced from this donor cell type only after aggregation of cloned embryos with a parthenogenetic blastomere. Our study demonstrates that the levels of histone acetylation in donor cells and cloned embryos correlate with their developmental potential and may be a useful epigenetic mark to predict efficiency of SCNT in rabbits.

During the oestrous cycle, the bovine endometrium exhibits characteristic morphological and functional changes, which are mainly induced by progesterone (P₄), oestrogens and oxytocin. We studied the response of the endometrium to this changing hormonal environment at the transcriptome level using a custom-made cDNA microarray. Endometrium samples were recovered from Simmental heifers on days 0 (oestrus), 3.5 (metoestrus), 12 (dioestrus) and 18. The latter group was divided into animals with high (late dioestrus) and low P₄ levels (preoestrus). Significance analysis of microarrays revealed 269 genes exhibiting significant changes in their transcript levels during the oestrous cycle in distinct temporal patterns. Two major types of expression profiles were observed, which showed the highest mRNA levels during the oestrus phase or the highest levels during the luteal phase respectively. A minor group of genes exhibited the highest mRNA levels on day 3.5. Gene ontology (GO) analyses revealed GO categories related to extracellular matrix remodelling, transport, and cell growth and morphogenesis enriched at oestrus, whereas immune response and particular metabolic pathways were overrepresented at dioestrus. Generation of gene interaction networks uncovered the genes possibly involved in endometrial remodelling (e.g. collagen genes, TNC, SPARC, MMP2, MEP1B, TIMP1, TIMP2, HTRA1), regulation of angiogenesis (e.g. ANGPTL2, TEK, NPY, AGT, EPAS1, KLF5 ), regulation of invasive growth (e.g. PCSK5, tight junction proteins, GRP, LGALS1, ANXA2, NOV, PLAT, MET, TDGF1, CST6, ITGB4), cell adhesion (e.g. MUC16, LGALS3BP) and embryo feeding (e.g. SLC1A1, SLC11A2, SLC16A1, SEPP1, ENPP1). Localisation of mRNA expression in the endometrium was analysed for CLDN4, CLDN10, TJP1, PCSK5, MAGED1, and LGALS1.

We established a short-term (24 h) culture system for bovine oviduct epithelial cells (BOECs), obtained on day 3.5 of the estrous cycle and evaluated the cells with respect to morphological criteria, marker gene expression, and hormone responsiveness. BOEC sheets were isolated mechanically from the ampulla with similar yields from oviducts ipsi- and contralateral to the ovulation site (57.9 ± 4.6 and 56.4 ± 8.0 × 10⁶ cells). BOECs showed > 95% purity and cells cultured for 24 h maintained morphological characteristics present in vivo, as determined by light microscopy, scanning electron microscopy, and transmission electron microscopy. Both secretory cells with numerous secretory granules and ciliated cells with long, well-developed, and vigorously beating kinocilia were visible. Quantitative real-time PCR failed to detect significant differences in transcript levels between ipsi-and contralateral BOECs for the majority of marker genes (estrogen receptors α and β (ESR1 and ESR2), 3-hydroxy-3-methylglutaryl-coenzyme A reductase (HMGCR), oviductal glycoprotein 1 (OVGP1), progesterone receptor (PGR), and tumor rejection antigen 1 (TRA1)) throughout the 24 h culture period. However, the combined data of all time points for glutathione peroxidase 4 (GPX4), a gene previously shown to be expressed at higher levels in the ipsilateral oviduct in vivo, also indicated significantly different mRNA levels in vitro. The expression of marker genes remained stable after 6 h cell culture, indicating only a short adaptation period. Western blot analysis confirmed ESR1 and PGR protein expression throughout the culture period. In agreement with cyclic differences in vivo, estradiol-17β stimulation increased PGR transcript abundance in BOECs. Our novel culture system provides functional BOECs in sufficient quantities for holistic transcriptome and proteome studies, e.g. for deciphering early embryo–maternal communication.

The most successful development of interspecies somatic cell nuclear transfer (iSCNT) embryos has been achieved in closely related species. The analyses of embryonic gene activity in iSCNT embryos of different species combinations have revealed the existence of significant aberrations in expression of housekeeping genes and genes dependent on the major embryonic genome activation (EGA). However, there are many studies with successful blastocyst (BL) development of iSCNT embryos derived from donor cells and oocytes of animal species with distant taxonomical relations (inter-family/inter-class) that should indicate proper EGA at least in terms of RNA polymerase I activation, nucleoli formation, and activation of genes engaged in morula and BL formation. We investigated the ability of bovine, porcine, and rabbit oocytes to activate embryonic nucleoli formation in the nuclei of somatic cells of different mammalian species. In iSCNT embryos, nucleoli precursor bodies originate from the oocyte, while most proteins engaged in the formation of mature nucleoli should be transcribed from genes de novo in the donor nucleus at the time of EGA. Thus, the success of nucleoli formation depends on species compatibility of many components of this complex process. We demonstrate that the time and cell stage of nucleoli formation are under the control of recipient ooplasm. Oocytes of the studied species possess different abilities to support nucleoli formation. Formation of nucleoli, which is a complex but small part of the whole process of EGA, is essential but not absolutely sufficient for the development of iSCNT embryos to the morula and BL stages.

Amino acids (AAs) are crucial for the developing conceptus prior to implantation. To provide insights into the requirements of the bovine embryo, we determined the AA composition of the uterine fluid. At days 12, 15, and 18 post-estrus, the uteri of synchronized pregnant and non-pregnant Simmental heifers were flushed for the analysis of 41 AAs and their derivatives by liquid chromatography–tandem mass spectrometry. The ipsilateral endometrium was sampled for quantitative PCR. In addition to a pregnancy-dependent increase of the essential AAs (P<0.01), we detected elevated concentrations for most non-essential proteinogenic AAs. Histidine (His) and the expression of the His/peptide transporter solute carrier 15A3 (SLC15A3) were significantly increased at day 18 of pregnancy in vivo. In addition, SLC15A3 was predominantly stimulated by trophoblast-derived interferon-τ in stroma cells of an in vitro co-culture model of endometrial cells. Our results show an increased concentration of AAs most likely to optimally provide the elongating pre-attachment conceptus with nutrients.

The mechanisms underlying detachment of foetal membranes after birth in cows are still unclear. To address this problem in a systematic manner, we performed the first holistic transcriptome study of bovine placentomes antepartum (AP; n=4 cows) and intrapartum (IP; n=4 cows) using Affymetrix GeneChip Bovine Genome Arrays. Three placentomes were extracted from each cow, and tissue samples from the contact zones of the placentomes (foeto-maternal units) were recovered by systematic random sampling and processed for RNA extraction and for stereological quantification of cellular composition. Statistical analysis of microarray data (false discovery rate 1%) revealed 759 mRNAs with at least twofold higher levels in the samples of the AP group, whereas 514 mRNAs showed higher levels in the IP group. The differentially expressed genes were classified according to biological processes and molecular functions using the Functional Annotation Clustering tool of the DAVID Bioinformatics Resources. Genes with higher mRNA levels in the AP group were nearly completely related to mitotic cell cycle and tissue differentiation. During parturition, a complete shift occurred because the genes with higher mRNA levels in IP were nearly all related to three different physiological processes/complexes: i) apoptosis, ii) degradation of extra cellular matrix and iii) innate immune response, which play a fundamental role in placental detachment. These results are an excellent basis for future studies investigating the molecular basis of retained foetal membranes.

The endometrium plays a central role among the reproductive tissues in the context of early embryo–maternal communication and pregnancy. This study investigated transcriptome profiles of endometrium samples from day 18 pregnant vs non-pregnant heifers to get insight into the molecular mechanisms involved in conditioning the endometrium for embryo attachment and implantation. Using a combination of subtracted cDNA libraries and cDNA array hybridisation, 109 mRNAs with at least twofold higher abundance in endometrium of pregnant animals and 70 mRNAs with higher levels in the control group were identified. Among the mRNAs with higher abundance in pregnant animals, at least 41 are already described as induced by interferons. In addition, transcript levels of many new candidate genes involved in the regulation of transcription, cell adhesion, modulation of the maternal immune system and endometrial remodelling were found to be increased. The different expression level was confirmed with real-time PCR for nine genes. Localisation of mRNA expression in the endometrium was shown by in situ hybridisation for AGRN, LGALS3BP, LGALS9, USP18, PARP12 and BST2. A comparison with similar studies in humans, mice, and revealed species-specific and common molecular markers of uterine receptivity.