Transcriptome and proteome analysis of early embryonic mouse brain development

Embryonic mouse brain development involves a sequential differentiation of multipotent progenitor cells into neurons and glia. Using microarrays and large 2-D electrophoresis, we investigated the transcriptome and proteome of mouse brains at embryonic days 9.5, 11.5 and 13.5. During this developmental period, neural progenitor cells shift from proliferation to neuronal differentiation. As expected, we detected numerous expression changes between the time points investigated but interestingly, the rate of alteration was about 10% to 13% of all proteins and mRNAs during every two days of development. Furthermore, up- and downregulation was balanced. This was confirmed for two additional stages of development, embryonic day 16 and 18. We hypothesize that during embryonic development, the rate of protein expression alteration is rather constant due to a limitation of cellular resources such as energy, space and free water. The similar complexity found at the transcriptome and proteome level at all stages suggests, that changes in relative concentration of gene products rather than an increased number of gene products dominate throughout cellular differentiation. We found that metabolism and cell cycle related gene products were downregulated in expression when precursor cells switched from proliferation to neuronal differentiation (day 9.5 to 11.5), whereas neuron specific gene products were upregulated. A detailed analysis revealed their implication in differentiation related processes such as rearrangement of the actin cytoskeleton as well as Notch and Wnt signaling pathways. Keywords: time course, development, transcriptome, proteome 3 embryonic stages: E9.5: 6 biological replicates E11.5: 4 biological replicates E13.5: 6 biological replicates