The segregation of the trophectoderm (TE) from the inner cell mass (ICM) in the mouse blastocyst is determined by position-dependent Hippo signaling. However, the window of responsiveness to Hippo signaling, the exact timing of lineage commitment and the overall relationship between cell commitment and global gene expression changes are still unclear. Single-cell RNA sequencing during lineage segregation revealed that the TE transcriptional profile stabilizes earlier than the ICM and prior to blastocyst formation. Using quantitative Cdx2-eGFP expression as a readout of Hippo signaling activity, we assessed the experimental potential of individual blastomeres based on their level of Cdx2-eGFP expression and correlated potential with gene expression dynamics. We find that TE specification and commitment coincide and occur at the time of transcriptional stabilization, whereas ICM cells still retain the ability to regenerate TE up to the early blastocyst stage. Plasticity of both lineages is coincident with their window of sensitivity to Hippo signaling.

Exposure of the preimplantation embryo to heat stress triggers a series of cellular, molecular, and adaptive changes preventing a normal embryonic development. Heat stress disrupts the embryo cytoskeleton, intracellular calcium levels, mitochondrial function, and induces apoptosis. Moreover, heat stress can act indirectly through induction of reactive oxygen species (ROS), leading to a variety of cellular damage. Embryonic resistance to heat shock is determined by factors such as genotype, developmental stage, apoptosis, redox status, and regulatory molecules. The early embryo is very susceptible to heat stress; it acquires resistance to elevated temperature as development advances. One of the mechanisms involved in the developmental acquisition of thermotolerance is heat‐induced apoptosis, which acts as a quality control mechanism to remove damaged blastomeres allowing the embryo to survive after stress. Although embryos at >8‐cell stage can activate the apoptotic cascade as an adaptive response to stress, embryos at the two‐cell stage are resistant to proapoptotic signals. This lack of apoptotic response has been associated to mitochondrial resistance to depolarization and epigenetic regulations, such as DNA methylation and histone deacetylation. Even though the cellular mechanisms triggered by heat stress have been studied, very little attention has been paid to the vulnerability of the epigenome to drastic temperature changes during the preimplantation period. Therefore, this review aims to characterize the effects of elevated temperature on the bovine embryo, especially addresissing developmental, cellular, and epigenetic alterations triggered in response to temperature.

Sperm chromatin integrity is essential for accurate transmission of male genetic information, and normal sperm chromatin structure is important for fertilization. Protamine is a nuclear protein that plays a key role in sperm DNA integrity, because it is responsible for sperm DNA stability and packing until the paternal genome is delivered into the oocyte during fertilization. Our aim was to investigate protamine deficiency in sperm cells of Bos indicus bulls (Nelore) using chromomycin A₃ (CMA₃) staining. Frozen semen from 14 bulls were thawed, then fixed in Carnoy's solution. Smears were prepared and analyzed by microscopy. As a positive control of CMA₃ staining, sperm from one bull was subjected to deprotamination of nuclei. The percentage of CMA₃-positive bovine sperm did not vary among batches. Only two bulls showed a higher percentage of CMA₃-positive sperm cells compared to the others. CMA₃ is a simple and useful tool for detecting sperm protamine deficiency in bulls.