The effect of the rat immunoglobulin heavy-chain 3' enhancer is position dependent.

We tested the effect of the immunoglobulin (Ig) heavy- and kappa-chain 3' enhancers on the expression of Ig genes in B-cells. Inclusion of the heavy-chain 3' enhancer in addition to the mu intron enhancer increased the expression rate up to sixfold, but this effect was strongly position dependent, in that it was only observed when the element was located downstream from the constant exons. Furthermore, the stimulatory effect could be augmented by increasing the distance between the constant gene segments and the 3' enhancer. When the 3' enhancer was located upstream from the variable gene promoter, the transcription was dramatically suppressed. Thus, the heavy-chain 3' enhancer does not fit into the usual definition of an enhancer element. The implications for the production of recombinant antibodies are discussed.

Construction of chimeric antibodies: cloning of immunoglobulin genes including their promoter regions by PCR.

In the production of recombinant antibodies, it is necessary to have an immunoglobulin gene promoter for driving the expression of the antibody genes. Here we describe a simple PCR method that allows cloning of the immunoglobulin genes together with their own promoters despite the fact that the sequence of the upstream part of the gene is unknown.

Rapid isolation of immunoglobulin variable genes from cell lysates of rat hybridomas by polymerase chain reaction.

The isolation of the rearranged immunoglobulin genes from a hybridoma cell line, which is a prerequisite for the construction of a recombinant antibody, can easily be achieved by polymerase chain reaction. Here we demonstrate that this method, which was originally described for cloning murine immunoglobulin genes from cDNA, is also applicable for rat genes. We show that the procedure also works with crude cell lysates as starting material, thereby greatly reducing the time required for sample preparation. In addition we have sequenced the nonfunctional heavy chain variable gene of the fusion partner X63Ag8.653, which was readily amplified from our hybridoma cells, and whose sequence has been so far unknown.

Selective elimination of the contact site A protein of Dictyostelium discoideum by gene disruption.

The contact site A glycoprotein is a developmentally regulated cell-surface component expressed during the aggregation stage of Dictyostelium discoideum. This protein has been implicated in the EDTA-stable (Ca2(+)-independent) type of cell adhesion of aggregating cells. The gene coding for the contact site A protein was disrupted by homologous recombination, using a transformation vector that contained a 1.0-kb cDNA fragment as an insert. Transformants that did not express the protein were identified by colony immunoblotting. These transformants produced three truncated contact site A transcripts. One of them was controlled by the original contact site A promoter, as indicated by its strict developmental regulation and cAMP inducibility; the other two transcripts were transcribed from the actin 6 promoter of the vector. When cell adhesion was assayed in the transformants by agitating suspended cells in an agglutinometer, EDTA-stable adhesion was drastically reduced as compared to wild type, confirming that the contact site A glycoprotein acts as a cell-adhesion molecule. However, aggregation of the transformed cells on an agar surface was not remarkably altered. These results suggest that the contact site A glycoprotein is responsible for a 'fast' type of cell adhesion that is essential when aggregating cells are subjected to shear. When cells are not mechanically disturbed, a 'slow' type of adhesion mediated by other molecules is sufficient for their aggregation.

Probing an adhesion mutant of Dictyostelium discoideum with cDNA clones and monoclonal antibodies indicates a specific defect in the contact site A glycoprotein.

Expression of developmentally regulated membrane proteins of aggregating cells of Dictyostelium discoideum is subject to several control mechanisms. One of them involves periodic cyclic-AMP pulses as signals for gene expression. To increase the probability of selecting mutants specifically defective in the contact site A (csA) glycoprotein, one of the characteristic proteins of aggregating cells, we have bypassed the requirement for both cyclic-AMP pulses and another control element by two runs of mutagenesis. A ;double bypass' mutant, HG592, was obtained which aggregated in nutrient medium where wild-type did not develop. Mutants defective in expression of the csA-glycoprotein were selected from HG592 by fluorescence-activated cell sorting and colony immunoblotting using a monoclonal antibody specific for that protein. One among 51 csA-negative mutants, HG693, specifically lacked the capability of forming EDTA-stable intercellular contacts. It acquired chemotactic responsiveness and developed into fruiting bodies. Expression of the transcripts for eight developmentally regulated proteins was determined in HG693. Seven of the RNA species were normally expressed; they were recognized by cDNA clones which had been produced from poly(A) RNA isolated from membrane-bound polysomes. The single RNA species which was not substantially expressed in HG693 was recognized by a cDNA clone that was obtained by screening a lambdagt11 library with an antibody specific for the csA-glycoprotein. When probing RNA from wild-type cells, this clone hybridized with a single developmentally regulated RNA species of 1.9 kb whose expression was strongly enhanced by cyclic-AMP pulses. Appearance of this RNA coincided with the expression of the csA-glycoprotein.