ABSTRACT: Understanding the pattern of gene expression and identifying the specific genes expressed during erythropoiesis is crucial for a synthesis of erythroid developmental biology. Here we have isolated four distinct populations of erythroblasts at successive erythropoietin-dependent stages of erythropoiesis including the terminal, pyknotic stage. The transcriptome has been determined using Affymetrix arrays. First, we show that cells sorted by surface expression profile express not only significantly fewer genes than unsorted cells, but also significantly more differences in the expression levels of particular genes between stages than unsorted cells, demonstrating the importance of working with defined cell populations to identify lineage and temporally-specific patterns of gene expression. Second, using standard software and matched filtering we identify eleven differentially regulated genes and one continuously expressed gene previously undetected in erythroid expression studies with unknown roles in erythropoiesis (CA3, CALB1, CTSL2, FKBP1B, GSDMB, ITLN1, LIN7B, RRAD, RUNDC3A, UNQ1887, ZNF805, MYL12B). Finally, using transcription factor binding site analysis we identify potential transcription factors that may regulate gene expression during terminal erythropoiesis. Our stringent lists of differentially regulated and continuously expressed transcripts are a resource for functional studies of erythropoietic protein function and gene regulation. PBMC-derived erythroblasts grown in vitro were harvested at the CFU-E, Pro-E, Int-E and Late-E stages and FACS sorted based on expression of cell surface markers. RNA was extracted from those populations which met rigorous specifications of time cultured in the presence of erythropoietin, morphology and CD36, CD71 and CD235a expression. For each stage, 3 chips were hybridised, each representing a pool of 4 different samples. In addition to these 12 chips, one chip representing a pool of RNA extracted from unsorted cells at each stages was also hybridised.
