Genomic Structure and Transcriptional Regulation of the Early B Cell GenechB1

Abstract

The avian B cell differentiation Ag chB1 is a membrane glycoprotein relative of the mammalian B cell differentiation Ag CD72. Unlike CD72, this C-type lectin is expressed in relatively high levels on immature B cells in the bursa of Fabricius and is down-regulated on mature B cells in the periphery. An immunoreceptor tyrosine-based inhibitory motif in the chB1 cytoplasmic tail suggests a potential regulatory role in intrabursal B cell development. To gain further insight into the selective expression and function of chB1, we determined the genomic organization of chB1 and examined the mechanism of its transcriptional regulation. The 8-exon chB1 gene proved to have very similar organization to that of mouse CD72, further supporting the idea that chB1 is a CD72 relative. As for mouse CD72, the chB1 promoter region lacks a TATA box but contains a conserved initiator element. The 131-bp region (−161 to −30) proximal to the transcriptional start site, which contains a potential early B cell factor binding site, is essential for the B lineage stage-specific transcription of chB1, whereas PU.1 and B cell-specific activator protein/Pax5 have been shown to play important roles in CD72 promoter activity and cell-type specificity. This analysis suggests that differences in transcriptional regulation of these phylogenetically related genes may determine the differences in expression pattern and, therefore, the function of avian chB1 and mammalian CD72 during B cell development.

Molecular mechanisms of primary and secondary mucosal immunity using avian infectious bronchitis virus as a model system

“…A number of genes important in triggering B cell activation were up-regulated after primary immunization. The signaling molecules responsible for B cell activation and differentiation included CD80-like costimulator (2.7-, 2.8-, 3.9-fold for d1, d5, and d21), B cell maturation promoting cytokine PBEF (pre-B cell enhancing factor, 5.6-, 2.3-, 2.5-, 2.0-fold for d1, d3, d5, and d12), Th2 promotion factor SOCS3 (suppressor of cytokine signaling 3, 8.3-, 2.8-, 2.1-fold for d1, d3, and d5) (Seki et al, 2003), B cell adaptor protein (BCAP, 2.8-, 5.0-, 2.6-, 6.4-, 3.0-fold for d3, d5, d8, d21, and d24), adaptor and scaffold protein of SAM-domain protein SAMSN-1 (3.6-, 3.1-, 5.5-fold for d1, d3, and d5) (Zhu et al, 2004), avian B cell differentiation antigen chB1 (3.3-, 3.9-, 3.1-fold for d1, d3, and d5) (Goitsuka et al, 2001), zeste homolog enhancer EZH2 (2.1-, 2.9-, 6.5-, 2.7-fold for d1, d3, d5 and d21) for IgH rearrangement regulation, immunoglobulin heavy chain binding protein BIP (3.5-, 3.3-, 6.0-, 6.2-, and 2.8-fold for d1, d3, d5, d21, and d24), and syndecan-1/CD138 (4.4-, 2.3-, 4.2-, 3.4-fold for d1, d3, d5, and d21) on Ig secreting plasma cells (Fig. 3).…”

Base Usage and Dinucleotide Frequency of Infectious Bursal Disease Virus

“…Since the database was constructed using a non-normalized cDNA library, the most frequently identified chicken (Callus gallus) genes will be the most abundantly (or highly) expressed genes in the bursa [59]. In addition, highly expressed bursal genes from other sources [60] were also included. Therefore the 28 highly expressed genes used in the analysis were ribosomal (16 sequences), heat shock (two sequences), elongation factor 1-a, b-actin, Ig rearranged light-chain VJC, chicken germ line Ig light chain, DEAD-box RNA helicase, non-histone chromosomal protein HMG-17, MHC B complex, ATF4, Bu-la, and chBl genes.…”

A novel avian homologue of CD72, chB1r, down modulates BCR-mediated activation signals

“…A 30-kb genomic clone containing the chB1 gene was previously isolated from a chicken genomic library constructed in the pWE15 cosmid vector (BD Clontech, Palo Alto, CA, USA) (11). After detailed restriction enzyme mapping of this genomic clone (see Fig.…”

“…We previously identified an avian C-type lectin gene named chB1 that encodes a protein with a homology to mammalian CD72 (10,11). Although the genomic structure of chB1 is very similar to that of mouse CD72 (11,12), the expression patterns and functions of chB1 and CD72 are not.…”

“…We previously identified an avian C-type lectin gene named chB1 that encodes a protein with a homology to mammalian CD72 (10,11). Although the genomic structure of chB1 is very similar to that of mouse CD72 (11,12), the expression patterns and functions of chB1 and CD72 are not. ChB1 is expressed primarily on B cells in the bursa of Fabricius and the DT40 B cell line (10), both of which are in the immature stage of B cell development and undergo diversification of their Ig genes by gene conversion.…”