Growing muscle tissue in culture from animal stem cells to produce meat theoretically eliminates the need to sacrifice animals. So-called "cultured" or "synthetic" or "in vitro" meat could in theory be constructed with different characteristics and be produced faster and more efficiently than traditional meat. The technique to generate cultured muscle tissues from stem cells was described long ago, but has not yet been developed for the commercial production of cultured meat products. The technology is at an early stage and prerequisites of implementation include a reasonably high level of consumer acceptance, and the development of commercially-viable means of large scale production. Recent advancements in tissue culture techniques suggest that production may be economically feasible, provided it has physical properties in terms of colour, flavour, aroma, texture and palatability that are comparable to conventional meat. Although considerable progress has been made during recent years, important issues remain to be resolved, including the characterization of social and ethical constraints, the fine-tuning of culture conditions, and the development of culture media that are cost-effective and free of animal products. Consumer acceptance and confidence in in vitro produced cultured meat might be a significant impediment that hinders the marketing process. (Résumé d'auteur

Successful production of high quality blastocysts in vitro depends on the use of a culture system that ensures the acquisition of developmental competence by the maturing oocyte. It is now clear that the in vitro maturation environment has a major influence on the oocyte's ability to acquire the potential to develop into blastocysts. In this work we examine the impact of oocyte culture media on the quality of blastocysts by comparing developmental rates, cell number and their allocation to embryonic cell lineages, apoptosis, and expression of developmentally important genes. Higher total cell count and ICM:TCN ratio, which are indicative of embryo viability, were observed in embryos derived from oocyte maturation in TCM-199 supplemented with serum when compared to blastocysts derived from oocyte maturation in SOF BSA. Moreover, oocyte maturation in TCM-199 supplemented with serum-generated embryos of higher morphological quality and producing higher levels of Interferon Tau transcripts when compared to embryos derived from oocyte maturation in SOF BSA. In conclusion, the oocyte maturation regimen affected the morphological feature of blastocysts, including total cell count and allocation of cells to trophectoderm (TE) and inner cell mass (ICM) lineages and the expression profiles of genes involved in various embryo functions such as early embryonic growth, regulation of gene transcription, trophoblast differentiation and function, embryo-maternal communication, and stress response. Our results show that the oocyte culture media have strong impact on the quality of embryos produced in vitro and emphasize the need for more in depth evaluation of oocyte maturation protocols.

Embryonic stem (ES) cell-derived clones and chimeras are often associated with growth abnormalities during fetal development, leading to the production of over/under-weight offspring that show elevated neonatal mortality and morbidity. Due to the role played by imprinted genes in controlling fetal growth, much of the blame is pointed at improper epigenetic reprogramming of cells used in the procedures. We have analyzed the expression pattern of two growth regulatory imprinted genes, namely insulin like growth factor II (Igf2) and H19, in mouse ES cells cultured under growth restricted conditions and after in vitro aging. Culture of cells with serum-depleted media (starvation) and at high cell density (confluence) increased the expression of both imprinted genes and led to aberrant methylation profiles of differentially methylated regions in key regulatory sites of Igf2 and H19. These findings confirm that growth constrained cultures of ES cells are associated with alterations to methylation of the regulatory domains and the expression patterns of imprinted genes, suggesting a possible role of epigenetic factors in the loss of developmental potential.

Pluripotent embryonic stem cells are able to differentiate into a variety of cell types, thereby making them a valuable source for transplantation medicine. Recent studies have reported the use of pharmacological agents, namely 5-Aza-Cytidine (5AzaC) and Trichostatin A (TSA), to guide embryonic stem (ES) cells to differentiate into specific cellular lineages. However, those drugs are known to be potent inhibitors of DNA methyltransferases and/or histone deacetylases. Since both epigenetic mechanisms are involved in the expression of imprinted genes in fetal and adult somatic tissues, it is essential to investigate further the role of these agents in regulating imprinted gene expression in embryonic cells. Embryonic stem cells were exposed to 5AzaC and TSA and analyzed for transcript abundance of a number of imprinted and non-imprinted marker genes. Most imprinted gene transcripts increased following exposure to 5AzaC or TSA alone and responded in either an additive or synergistic manner when exposed to both drugs together. Interestingly, transcript levels of several imprinted genes remained high and in some cases, increased further after drug removal or even after passaging the cells, indicating a long lasting and retarded effect on gene expression. Together, our results suggest that DNA methylation and histone acetylation play jointly an important epigenetic role in governing imprinted gene expression in embryonic stem cells. Moreover, these results describe the sensitivity and irreversibility of embryonic stem cells to epigenetic modifiers, highlighting potential risks for their use in therapeutic applications.

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