The commitment of secretory cells to the selective expression of immunoglobulin CH genes is determined by the available concentrations of the triggering ligand

Rearrangement and expression of rabbit immunoglobulin kappa light chain gene in transgenic mice

To determine whether a foreign unrearranged immunoglobulin gene can be functionally rearranged and expressed in vivo, a rabbit b9 kappa light chain gene construct containing a single germ-line kappa chain variable (V) region gene (V kappa), the five kappa chain joining (J) segments (J kappa), and the kappa chain constant (C) region germ-line gene (C kappa) was introduced into fertilized mouse eggs. Eleven transgenic mice carrying 1-30 copies of the rabbit kappa gene construct were obtained. Rearrangement of the transgene due to V kappa-J kappa recombination was observed in the spleen of all the mice lines analyzed. Only the J kappa 1 and J kappa 2 segments, which have canonical sequences for rearrangement and high-level expression, are utilized in assembly of the rabbit gene. V kappa-J kappa 1 and V kappa-J kappa 2 joining was also observed in the thymus but not in nonlymphoid tissue. Polyadenylylated rabbit kappa chain transcripts of 1.2 kilobases were found in the spleen of the transgenic mice. The level of transcription was low despite a high level of rearrangement. Three transgenic mice lines secreted kappa light chains encoded by the foreign rabbit gene. Serum rabbit kappa chains were associated with mouse mu and gamma 1 heavy chains. However, hybrid antibody molecules containing both rabbit and mouse kappa light chains were also found in the serum of these animals. These results suggest that, although the rabbit kappa chain gene construct contains the necessary sequences for gene assembly, sequences implicated in stage- and tissue-specific regulation of kappa chain gene rearrangement are either missing or not recognized by mouse lymphoid cells.