Postnatal days 1, 18 and 21 were chosen to reflect early development prior to white matter establishment and the peak of oligodendrocye differentiation and myelin ALK5 Inhibitor II ALK inhibitor synthesis . For each time point, total RNA was isolated from the entire brain excluding the cerebellum of 3 wild-type and 3 mutant mice, followed by genome-wide measurement of mRNA expression by Affymetrix microarray . At each time point, between 441 and 818 genes were differentially expressed in the eIf2b5 R132H mutant mice . There was surprisingly little overlap between the sets of genes dysregulated at different time points . The differential expression of a total of 7 representative genes was validated by qRT-PCR . The unique time-point-specific differential gene expression signature suggests that the altered global protein synthesis in mutant mice elicits a unique response depending on the developmental stage of the brain. Each set of differentially-expressed genes was analyzed for enrichment of gene sets known to share a common function or gene sets previously reported to share common expression patterns during mouse development . Interestingly, the gene set differentially expressed at P1 was enriched with genes related to cell-cycle progression, whereas the gene set differentially expressed at P21 was enriched with oligodendrocyte-specific genes. Of the 44 cell-cycle associated genes the expression of which was low in the mutant brain at P1, 11 were related to mitosis . During early postnatal stages, brain cells undergo multiple divisions . Thus, lower expression level of mitotic genes may adversely affect cell proliferation during this critical developmental stage. This is consistent with the recentlyreported delayed brain development of Eif2b5-mice . Interestingly, during normal mice brain development , all 44 cell-cycle associated genes are highly expressed immediately after birth and down-regulated thereafter . A similar trend was observed in the current study using wild-type mice, in which these specific genes were highly expressed at P1 and then down-regulated at P18 and P21 . However, in mutant mice, the expression level of each of these genes was significantly lower at P1 , indicating that Eif2b5 mutation either suppresses the up-regulation of cell-cycle associated genes immediately after birth or induces their premature down-regulation at P1 instead of at a later time point . The lower level of two mRNAs, cyclin A2 and cyclin B1, was further validated by BYL719 qRTPCR . Since both cyclin A2 and cyclin B1 are required for progression through mitosis, their decreased expression level is expected to prolong mitosis . To assess the progression of Eif2b5-mutated cells through the cell cycle, primary astrocytes were isolated from the brains of wild type and mutant newborn mice and subjected to flow cytometry analysis following propidium iodide staining of their DNA.