ABSTRACT: THOC5, a member of the mRNA export complex, is essential for hematopoiesis in vivo and is required for CSF-1 induced macrophage differentiation, thereby playing a key role in the mRNA export of immediate early genes induced by CSF-1 stimulation. Hematopoiesis, growth, differentiation, and commitment to a restricted lineage are guided by a timely expressed set of cytokine receptors and their down-stream transcription factor genes. Transcriptional control mechanisms of gene expression during differentiation were mainly studied by focusing on the cis- and trans-element in promoters, however, the role of mRNA export machinery during differentiation have not been adequately examined. A member of the mRNA export complex, THOC5 which is a substrate for the macrophage-colony stimulating factor (CSF-1) receptor, ATM kinase, or protein kinase C, is an essential element in the maintenance of hematopoiesis in adult mice. Using tamoxifen inducible THOC5 knockout mice, we show here that the depletion of THOC5 impaired myeloid differentiation, but does not influence terminally differentiated organs. Furthermore, an in vitro study showed that the depletion of THOC5 in bone marrow cells results in abnormal CSF-1 induced macrophage differentiation. Transcriptome analysis using cytoplasmic RNA derived from macrophages reveals that only 99 genes were down-regulated 3 days after the depletion of THOC5, however, immediate early genes induced by CSF-1 stimulation, such as Ets family genes, and regulators of myeloid differentiation HoxA1, Id1, Id3 were THOC5 direct target mRNAs, suggesting that THOC5 plays a key role in myeloid differentiation. In each of two biological experiments (called rep1 and rep2 below) six different cytoplasmic RNA samples were generated from bone marrow derived macrophages. These different samples (conditions) correspond to: 1) Cells from ERT2 Cre control mice at day 0, 2) Cells from ERT2 Cre control mice at day 3 of differentiation, 3) Cells from ERT2 Cre control mice at day 3 of differentiation stimulated with tamoxifen, 4) Cells from ERT2 Cre Thoc5 (flox/flox) mice at day 0, 5) Cells from ERT2 Cre Thoc5 (flox/flox) mice at day 3 of differentiation, 6) Cells from ERT2 Cre Thoc5 (flox/flox) mice at day 3 of differentiation stimulated with tamoxifen. Day 0 samples of a given genotype were utilized as common reference in two microarrays and were accordingly co-hydridized against both 3-days differentiated samples (treated or none with tamoxifen) of the same genotype and biological experiment. Thus, four dual-color microarrays from each of the two biological replicate series were performed (giving rise to 8 dual-color microarrays in total). The complete set of microarrays from the second biological experiment (rep2) was performed with inverted labeling directions (dye-swap approach).
