Discovery and functional validation of a novel miRNA cluster. (A) Genomic locus of the mir-2355 cluster (chromosome 9q34.3), conservation across 3 primates and one additional mammal (mouse), and predicted secondary structure of each miRNA hairpin, with the mature sequences highlighted in yellow. The sequencess are conserved only in primates. (B) Knockout of the primary miRNA transcript processing enzyme, Drosha, by RNA interference results in accumulation of a known miRNA cluster primary transcript (pri-hsa-mir-17) and the novel miRNA cluster primary transcript (pri-hsa-mir-2355). (C) Expression of hsa-miR-2355 is higher in GCBs compared with memory B cells. (D) Chromatin immunoprecipitation with an antibody to H3K4me3 of GCBs and memory B cells shows enrichment of DNA from the predicted core promoter region of the miR-2355 cluster in GCBs compared with memory B cells. Three sets are shown: input (positive control for PCR using chromatin before immoprecipitation), immunoprecipitation with an antibody for H3K4me3, and immunoprecipitation with an antibody for CD20 (negative control). (E) Gene set enrichment analysis score and distribution of TGF-β pathway genes along the rank of transcripts differentially expressed in high versus low expressors of the miR-2355 cluster. Expression of the TGF-β pathway genes were inversely correlated with expression of the miRNA.