Trichostatin A (TSA) is an inhibitor of histone deacetylase and is able to alter gene expression patterns by interfering with the removal of acetyl groups from histones. The aim of this study was to determine the effect of TSA treatment on the development and gene expression patterns of mouse zygotes developing in vitro. The addition of 100 nm TSA to the culture medium did not affect the cleavage of mouse embryos (TSA treatment, 148/150 (99%) v. control, 107/107 (100%)); however, embryos that were treated with TSA arrested at the 2-cell stage (145/148, 98%). We estimated the number of nuclei in control and TSA-treated embryos by propidium iodide staining, taking into account the presence of any cells with two or more nuclei. At 62–63 h post-hCG stimulation, control zygotes had developed to the 4-cell stage and exhibited one nucleus in each blastomere, indicative of normal development. In contrast, we observed tetraploid nuclei in at least one blastomere in 20.8% (11/53) of the embryos that had been treated with TSA. At 28–29 h post-hCG stimulation (metaphase of the 1-cell stage), there was no difference in the mitotic index (as determined by analyzing the microtubule configuration) in the TSA group compared to the control group. At the 2-cell stage, however, we did not observe mitotic spindles and metaphase chromatin in embryos in the TSA treatment group compared to the controls. Interestingly, when embryos were cultured in TSA-free medium from 35 h post-hCG stimulation (S- or early G2-phase of the 2-cell stage) onward, almost all of them (47/50) developed to the blastocyst stage. In contrast, when embryos were cultured in TSA-free medium from 42 h post-hCG stimulation (middle G2-phase of the 2-cell stage) onward, they did not develop to the 4-cell stage. We used Illumina microarray technology to analyze the gene expression profiles in control and TSA-treated late 2-cell-stage embryos. Applied Biosystems Expression System software was used to extract assay signals and assay signal-to-noise ratio values from the microarray images. Our data showed that 897 genes were significantly (P < 0.05; 2-sample t-test) up- or down-regulated by TSA treatment compared to controls. Analysis using the PANTHER classification system (https://panther.appliedbiosystems.com) revealed that the 575 genes that were differentially expressed in the TSA group compared to the control were classified as being associated with putative biological processes or molecular function. Overall, in terms of putative biological processes, more nucleoside, nucleotide, and nucleic acid metabolism, protein metabolism and modification, signal transduction, developmental process, and cell cycle genes were differentially expressed between the TSA and control groups. In terms of putative molecular function, more nucleic acid-binding transcription factor and transferase genes were differentially expressed between the groups. The results collectively suggest that inhibition of histone acetylation in mouse embryos affects gene expression profiles at the time of zygotic genome activation, and this subsequently affects further development.
Computational identification of similar gene expression patterns from images of mouse embryos