Exposure of chimaeric embryos to exogenous FGF4 leads to the production of pure ESC-derived mice.

Producing chimaeras constitutes the most reliable method of verifying the pluripotency of newly established cells. Moreover, forming chimaeras by injecting genetically modified embryonic stem cells (ESCs) or induced pluripotent stem cells (iPSCs) into the embryo is part of the procedure for generating transgenic mice, which are used for understanding gene function. Conventional methods for generating transgenic mice, including the breeding of chimaeras and tetraploid complementation, are time-consuming and cost-inefficient, with significant limitations that hinder their effectiveness and widespread applications. In the present study, we modified the traditional method of chimaera generation to significantly speed up this process by generating mice exclusively derived from ESCs. This study aimed to assess whether fully ESC-derived mice could be obtained by modulating fibroblast growth factor 4 (FGF4) levels in the culture medium and changing the direction of cell differentiation in the chimaeric embryo. We found that exogenous FGF4 directs all host blastomeres to the primitive endoderm fate, but does not affect the localisation of ESCs in the epiblast of the chimaeric embryos. Consequently, all FGF4-treated chimaeric embryos contained an epiblast composed exclusively of ESCs, and following transfer into recipient mice, these embryos developed into fully ESC-derived newborns. Collectively, this simple approach could accelerate the generation of ESC-derived animals and thus optimise ESC-mediated transgenesis and the verification of cell pluripotency. Compared to traditional methods, it could speed up functional studies by several weeks and significantly reduce costs related to maintaining and breeding chimaeras. Moreover, since the effect of stimulating the FGF signalling pathway is universal across different animal species, our approach can be applied not only to rodents but also to other animals, offering its utility beyond laboratory settings.

Determining the pathogenicity and virulence of parasites on animal models.

The aim of this review is to present various animal organisms used to determine the pathogenicity and virulence of old and new human and animal pathogens based on animal studies, cell cultures, macrophages and other models. The animal models presented in this study, in addition to the most popular organisms such as the laboratory mouse, rat, guinea pig and monkey, are also less popular models, such as zebrafish (Danio rerio) or chicken embryos in eggs. These animals are used to study the pathogenicity of parasites such as Acanthamoeba, Naegleria fowlerii, Toxoplasma gondii, Entamoeba histolytica and Besnoitia caprae and other species. In addition to animal models, we also present models using cell cultures, macrophages and computer methods. We also answer questions about what experimental methods allow to differentiate species and populations in terms of pathogenicity and virulence.