Cutting edge: Polycomb gene expression patterns reflect distinct B cell differentiation stages in human germinal centers

Polycomb group (Pc-G) proteins regulate homeotic gene expression in Drosoph ila, mouse, and humans, Mouse Pc-G proteins are also essential for adult he matopoietic development and contribute to cell cycle regulation. We show th at human Pc-G expression patterns correlate with different B cell different iation stages and that they reflect germinal center (GC) architecture. The transition of resting mantle B cells to rapidly dividing Mib-1(Ki-67)(+) fo llicular centroblasts coincides with loss of BMI-1 and RING1 Pc-G protein d etection and appearance of ENX and EED Pc-G protein expression. By contrast , differentiation of centroblasts into centrocytes correlates with reappear ance of BMI-1/RING1 and loss of ENX/EED and Mib-1 expression. The mutually exclusive expression of ENX/ EED and BMI-1/RING1 reflects the differential composition of two distinct Pc-G complexes, The Pc-G expression profiles in various GC B cell differentiation stages suggest a role for Pc-G proteins in GC development.