Developmental plasticity and transgenerational reprogramming following vitrified embryo transfer in oryctolagus cuniculus

Resumen

Assisted reproductive technologies involve the furthest change from the natural environment by failing to mimic optimal maternal conditions, and thereby entail consequences for late development. The general aim of this thesis was to study the long-term and transgenerational effects of the in vitro stressors occurring during a vitrified embryo transfer procedure on the rabbit model. In Chapter I, we prove that transferring early or compact morula leads to rates of survival at birth 70% in fresh and 55% after vitrification. The ease of performing both embryo cryopreservation and embryo transfer procedures, the high numbers of descendants that we are able to obtain and the short life cycle of the rabbit encouraged and facilitated the following studies. Chapter II was designed to compare the short and long-term developmental differences between animals born from fresh-transferred (FT) and vitrified-transferred (VT) embryos, using a naturally conceived (NC) population as control reference. Both prenatal survival rates and growth performance were significantly reduced as embryo manipulation was increased (NC FT VT). In addition, we compare the effect of two vitrification devices, noting that although cryotop exerted a positive effect on foetal survival, incurred higher phenotypic (growth and lactation performances) deviations postnatally than the straw device. Then, the choice of vitrification device is not trivial. However, all progenies were healthy and fertile. Therefore, these results demonstrated the high developmental plasticity of the mammalian embryo under different in vitro stressors. The aim of Chapter III was to evaluate the effects of the entire vitrified embryo transfer procedure (VET) on development, detecting that VT animals have modifications of the birth weight and growth pattern, but males were more affected than females. At adulthood, VT males were smaller and showed a significantly lower liver and heart weight than NC males. A comparative proteomic analysis showed changes in relation to oxidative phosphorylation and dysregulations in the zinc and lipid metabolism. However, a blood analysis (haematological and biochemical) revealed that health status was comparable between VT and NC animals. In Chapter IV, a three generation (F1, F2 and F3) model was constituted in order to assess the transgenerational effects of the VET. The results showed that direct (F1) effects of the VET were also intergenerational (F2) and transgenerational (F3), as VT progenies exhibited alterations in the growth velocity, adult body weight and liver weight in each generation. A comparative molecular (transcriptomic and metabolomics) study in the liver tissue unveiled alterations in the zinc and unsaturated fatty acid metabolism across the generations, which can be correlated with the VT phenotype. Nonetheless, similarities in the fertility between VT males and their NC counterparts in each generation denote that VET did not seem to impair the health status in the VT animals. Finally, in Chapter V, a comparative multi-omic (metabolomic, proteomic and epigenomic) approach was performed in the liver tissue between F3-VT and F3-NC animals. Both metabolomic and proteomic analyses showed global alteration in the hepatic metabolism of VT animals, mainly related to lipid metabolism (e.g. polyunsaturated fatty acids, steroids, steroid hormones¿). In addition, broad methylation changes were detected in the hepatic epigenome, involving genes related with lipid metabolism and apoptosis. These data demonstrated the transgenerational inheritance of the changes induced by VET in ancestors' embryos. The healthy status was similar between VT and NC animals. Through this thesis, it has been demonstrated for the first time that VET induces a developmental reprogramming that persists until adulthood and in subsequent generations, incurring long-term consequences for the phenotype and the molecular physiology of the resultant offspring.