Fighting Like Cats and Dogs: Challenges in Domestic Carnivore Oocyte Development and Promises of Innovative Culture Systems

SIMPLE SUMMARY: In assisted reproduction, in vitro embryo production is the generation of embryos from isolated gametes in an equipped laboratory. This procedure is commonly employed in humans as well as in animals to preserve or improve their fertility, but while it works well in some species, such as cattle, it still faces some challenges in others, such as cats and dogs, which are important animal models to develop assisted reproduction techniques for related wild, endangered species. Traditionally, gametes and embryos are cultured in vitro on glass or plastic dishes, but these supports are very different from the ovarian follicles, the oviducts, or the uterus, which are the physiological environments where oocytes and embryos grow and develop. This review article describes these culture systems, the cellular alterations that could arise from their use, and it illustrates innovative possibilities (e.g., three-dimensional or microfluidic cultures) that could improve the outcomes of in vitro cultured feline and canine reproductive cells. ABSTRACT: In vitro embryo production in cats and dogs still presents some challenges, and it needs to be optimized to transfer efficient protocols to related wild, endangered species. While the chemical composition of culture media has been the focus of several studies, the importance of culture substrates for oocyte and embryo culture has often been neglected. Traditional in vitro systems, i.e., two-dimensional cultures, do not resemble the physiological environments where cells develop, and they may cause morphological and functional alterations to oocytes and embryos. More modern three-dimensional and microfluidic culture system better mimic the structure and the stimuli found in in vivo conditions, and they could better support the development of oocytes and embryos in vitro, as well as the maintenance of more physiological behaviors. This review describes the different culture systems tested for domestic carnivore reproductive cells along the years, and it summarizes their effects on cultured cells with the purpose of analyzing innovative options to improve in vitro embryo production outcomes.