During mammalian preimplantation development, two successive differentiation events lead to the establishment of three committed lineages with separate fates: the trophectoderm, the primitive endoderm and the pluripotent epiblast. In the mouse embryo, the molecular mechanisms underlying these two cell fate decisions have been studied extensively, leading to the identification of lineage-specific transcription factors. Species-specific differences in expression patterns of key regulatory genes have been reported, raising questions regarding their role in different species. The aim of the present study was to characterise the gene expression patterns of pluripotency (OCT4, SOX2, NANOG) and differentiation (CDX2, GATA6)-related markers during feline early development using reverse transcription-quantitative polymerase chain reaction. In addition, we assessed the impact of in vitro development on gene expression by comparing transcript levels of the genes investigated between in vitro and in vivo blastocysts. To normalise quantitative data within different preimplantation embryo stages, we first validated a set of stable reference genes. Transcript levels of all genes investigated were present and changed over the course of preimplantation development; a highly significant embryo-stage effect on gene expression was observed. Transcript levels of OCT4 were significantly reduced in in vitro blastocysts compared with their in vivo counterparts. None of the other genes investigated showed altered expression under in vitro conditions. The different gene expression patterns of OCT4, SOX2, CDX2 and GATA6 in cat embryos resembled those described in mouse embryos, indicative of a preserved role for these genes during early segregation. However, because of the absence of any upregulation of NANOG transcription levels after embryonic genome activation, it is unlikely that NANOG is a key regular of lineage segregation. Such results support the hypothesis that the behaviour of early lineage markers can be species specific. The present study also revealed a pool of maternal NANOG mRNA transcripts, the role of which remains to be elucidated. Comparing transcription levels of these genes between in vivo and in vitro blastocysts revealed low levels of OCT4 mRNA in the latter, which may contribute to the reduced developmental competence of embryos under suboptimal conditions.

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Contents During the last decades, in vitro fertilization (IVF) has become a routine technique in most domestic animals. However, in the dog the technique has lagged behind, with to date not a single pup born after IVF. In cats, healthy kittens have been born, but in fewer numbers than in cattle and horses. In pet animals, research in reproduction has mainly been focused on contraception, although recently, the introduction of new drugs especially marketed for cats and dogs will probably expand fertility research in carnivores towards the previously neglected area of assisted reproduction. In particular, the dog remains a real challenge for the reproductive biologist, due to the low meiotic capacity of canine follicular oocytes. In cats, oocyte maturation is less of a problem and embryo production rates comparable to those of cattle can be achieved. The domestic cat is a valuable model for endangered felids and it can even be used as a recipient for wild felid embryos. In this short review, we list some of the problems associated with the implementation of IVF in dogs and cats in relation to their reproductive characteristics, and we discuss the state‐of‐the‐art of IVF in several other domestic species such as cattle, horses and pigs.