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We investigated the expression of differential light chains in human B cell lines secreting immunoglobulin (Ig). When these cell lines were cultured with concanavalin A for a long period of time, a subpopulation of some but not all of these cell lines was induced to express new light chains replacing the original chain (light chain shifting). Production of the new chain, which replaces the original chain, results from a VJ rearrangement at a previously excluded allele and a dramatic reduction of the original chain transcript, although no difference was found in the level of heavy chain transcript. Recombination activating genes RAG-1 and RAG-2, which are normally expressed during specific early stages of lymphocyte development, were expressed in not only the light chain shifting-inducible lines but also in the non-inducible cells. Treatment of these Ig secreting cell lines with dibutyryl cAMP, which is known to enhance expression of the RAG genes, could not induce the creation of new light chain-producing cells from the inducible lines, suggesting that the expression of the two RAG genes is not sufficient for inducing new light chain production. Concanavalin A induced a gradual but significant production lost of the original chain in a subpopulation of the light chain shifting-inducible cells but not in the non-inducible cells. Association of new light chain production with loss of original chain raises the possibility that, when the RAG genes are expressed, concanavalin A may act on a novel intracellular mechanism controlling light chain allelic exclusion in these plasma cell lines.

Six peptides belonging to the crustacean hyperglycemic hormone (CHH) family were isolated from extracts of the sinus glands of the giant tiger prawn Penaeus monodon by reverse-phase high-performance liquid chromatography. These were designated Pem-SGP-A to Pem-SGA-F (Pem, Penaeus monodon; SGP, sinus gland peptide) and their amino-terminal amino acid sequences were analyzed. Five of the 6 peptides (Pem-SGP-A, -B, -D, -E, and -F) exhibited similar amino acid sequences to those of CHH peptides that had been characterized previously from the same prawn species by the other research groups, while 1 peptide (Pem-SGP-C) exhibited a novel sequence. Pem-SGP-C showed sequence similarity to known putative molt-inhibiting hormones (MIHs), particularly to an MIH from the kuruma prawn Penaeus japonicus, and less similarity to the CHHs determined thus far. Two similar complementary DNAs encoding Pem-SGP-C were cloned and found to encode very similar but distinct peptides, which were named Pem-SGP-C1 and Pem-SGA-C2. The open reading frame of each cDNA consisted only of a signal peptide and an MIH-like peptide. We also cloned 2 corresponding genes, both of which consisted of 3 exons and 2 introns. Analyses by reverse transcriptase polymerase chain reaction demonstrated that both Pem-SGP-C1 and Pem-SGP-C2 transcripts were detected only in cDNA synthesized using total RNA from the eyestalk but not in that from brain, thoracic ganglia, abdominal ganglia, abdominal muscle, hepatopancreas, or heart tissue of P. monodon.

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