title: Diversity of expressed V and J regions of immunoglobulin light chains in Xenopus laevis.
abstract: In Xenopus laevis, two immunoglobulin light chain isotypes, designated L1 or rho and L2 or sigma, have been identified. The genomic organization of the L1 locus has been described previously: a constant (C) gene segment is preceded by a joining (J) gene segment; in addition, there are many cross-hybridizing variable (V) gene segments. To evaluate the extent of sequence diversity of L1 V regions, we screened three cDNA libraries, constructed from mitogen-stimulated Xenopus splenocytes, with probes for the C or the J gene segment. Eighteen cDNA clones that contain complete or truncated V regions were chosen for sequence analysis. The C regions of all clones are identical or nearly identical to the genomic C gene segment; the V regions are greater than 80% identical in nucleotide sequence and are presumably derived from a single family of V gene segments. Although framework regions are nearly identical, complementarity-determining regions are quite diverse. The expressed J segments fall into distinct groups, suggesting the presence of more than one germ-line J segment. Therefore, a genomic library was screened with a J region probe. A clone overlapping with the previously identified J-C clone, and containing four additional J gene segments, was isolated. All five J gene segments are very similar and three are identical in nucleotide sequence. Each of the three distinct germ-line J sequences is represented in the set of cDNA clones, suggesting that combinatorial diversification occurs; imprecision of V-J joining also appears to contribute to variability. Overall, these results suggest that the immunoglobulin repertoire in this species is not significantly restricted by a limitation in the diversity of light chain V regions.
authors.affiliation: Department of Biology, Massachusetts Institute of Technology, Cambridge 02139.
authors.forename: S E
authors.initials: SE
authors.lastname: Stewart
authors.forename: L
authors.initials: L
authors.lastname: Du Pasquier
authors.forename: L A
authors.initials: LA
authors.lastname: Steiner
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D004247:DNA / Q000737:chemistry; D005803:Genes, Immunoglobulin; D007133:Immunoglobulin Joining Region / Q000737:chemistry / Q000235:genetics*; D007147:Immunoglobulin Light Chains / Q000737:chemistry / Q000235:genetics*; D007135:Immunoglobulin Variable Region / Q000737:chemistry / Q000235:genetics*; D008969:Molecular Sequence Data; D014982:Xenopus laevis / Q000235:genetics / Q000276:immunology*
chemical_list: D007133:Immunoglobulin Joining Region; D007147:Immunoglobulin Light Chains; D007135:Immunoglobulin Variable Region; D004247:DNA