Transcriptional enhancers of immunoglobulin light chain genes in Atlantic cod (Gadus morhua)

The organization of immunoglobulin heavy (H) chain genes in teleosts resemb les that of mammals and amphibians, whereas light (L) chain genes are arran ged in multiple clusters of variable (VL), joining (JL), and constant (CL) region segments. Sequence analysis of two Atlantic cod genomic clones (14,9 66 and 13,116 bp in length) revealed a very compact IgL chain locus with th e VL genes in opposite transcriptional orientation to the JL and the CL gen es. This suggests the possibility of rearrangements between clusters by inv ersion. Each cluster spans approximately 2.1 kb and distances between clust ers vary between 2.1 and 4.8 kb. To gain insight into the transcriptional r egulation of this complex, multiclustered locus, chloramphenicol acetyl tra nsferase reporter constructs containing 14 different DNA segments from the two genomic clones were transfected into channel catfish B and non-B-cell l ines, as well as into mouse B-cell lines. These studies showed strong enhan cer activity downstream of the CL region in three out of six L chain gene c lusters when assayed in fish, but not in mouse B cells. Interestingly, both mouse and human lambda enhancers exhibited strong activity in the fish B c ells, while the mouse 3' kappa enhancer did not. This suggests that transcr iption factors similar to those involved in mammalian lambda expression are present in B cells from teleosts.