Distinct developmental regulation and properties of the responsiveness of different genes to cyclic AMP in Dictyostelium discoideum.

Cyclic AMP (cAMP) is known to be an important mediator of gene expression in eukaryotic cells. At present, little is known about the developmental events which render specific genes responsive to cAMP in distinct cell types, or about the biochemical mechanisms by which cAMP exerts these regulatory effects. By examining the effects of cAMP treatment on specific mRNA levels in Dictyostelium discoideum cells with different 'developmental histories', we defined the developmental states in which specific genes display responsiveness to cAMP. We focused on two specific rapid responses: the ability of cAMP to inhibit the expression of an 'early' developmentally regulated mRNA (discoidin-I) and to stimulate the expression of a 'late', prespore-specific mRNA (PL3). Using this approach, we showed that, for both mRNAs, the ability to respond rapidly to cAMP is absent from vegetative cells grown on bacteria, and is acquired during development on filters. Furthermore, we identified several developmental states in which the discoidin-I response to cAMP is present, but in which the PL3 response is not. In experiments designed to examine the effects of cAMP analogues on the levels of these two mRNAs, we demonstrated that the analogue specificities of the discoidin-I and PL3 responses are different, and that the specificity for the PL3 response depends on the developmental state. The developmental kinetics and analogue specificity of the PL3 response suggest a two-step mode of action of cAMP in activating the expression of this gene. We discuss possible implications of these findings for the mechanisms of action of exogenous cAMP as well as for the role of cAMP in controlling the changes in gene expression that accompany normal development.

Relationships between cell-cell interactions, cAMP, and gene expression in a developmental mutant of Dictyostelium discoideum.

Previous work has led us to propose that close cell-cell associations during D. discoideum development serve as a signal to deactivate expression of discoidin I mRNA, and that intracellular cAMP serves as a mediator of this regulatory pathway. This model is based in part on the failure of a morphogenetic mutant, EB-21, to deactivate discoidin I expression under conditions where these cells fail to acquire cell-cell cohesiveness and hence remain as single cells, unlike the wild type strain which forms multicellular aggregates. Here we show that the failure of EB-21 to express specific cohesiveness depends on developmental conditions, and that under conditions where close cell-cell associations are allowed to form, discoidin I mRNA expression is deactivated normally. Furthermore, in both wild type and EB-21 there is a close correlation between formation close cell-cell associations and elevation of intracellular cAMP under different developmental conditions. Additional analyses of the biological behavior of EB-21 indicate that it acquires a normal cAMP chemotactic signal-response system, and that the morphogenetic defect cannot be corrected by co-development with wild type cells. The results are discussed in terms of possible relationships between cell-cell interactions, cAMP metabolism, and developmental gene expression in this organism.

Immunological studies on the origin of the precursor cells in Waldenström's macroglobulinemia.

Preliminary results obtained with OK anti-T and FMC anti-B monoclonal antibodies in a study of peripheral blood lymphocytes from eight patients with Waldenström's macroglobulinemia and of bone marrow lymphocytes from three patients, are reported. Endocytoplasmic immunofluorescence revealed a 1 to 3% marrow plasma cell fraction in all three cases, together with an approximately 10% increase in the monoclonal precursor compartment. Displacement of the peripheral blood helper: suppressor ratio was also observed using anti-T-lymphocyte monoclonal antibodies.

Regulation of discoidin I gene expression in dictyostelium discoideum by cell-cell contact and cAMP.

We have previously presented evidence that cell-cell contact is the normal developmental signal to deactivate discoidin I gene expression in D discoideum [Berger EA, Clark JM: Proc Natl Acad Sci USA 80:4983, 1983]. Here we provide genetic evidence to support this hypothesis by examining gene expression in a cohesion-defective mutant, strain EB-21, which enters the developmental program but is blocked at the loose mound stage. When this strain was developed in suspension, the cells remained almost entirely as single amoebae, unlike the wild type, which formed large multicellular aggregates. In both strains, discoidin I mRNA levels were low in vegetative cells but rose sharply during the first few hours of development. However, the peak level reached at 8 hr in EB-21 exceeded that observed in wild type, and while the level declined markedly over the next few hours in wild type, it remained highly elevated in the mutant. Thus, there was a correlation between the inability of EB-21 to form normal cell-cell contacts and its deficiency in inactivating discoidin I gene expression. Previous studies from several laboratories, including this one, have demonstrated that exogenously added cAMP can block or reverse the changes in gene expression normally seen upon cell disaggregation. This has led us to propose that cAMP serves as a second messenger regulating the expression of contact-regulated genes. Here we provide additional support for this hypothesis. Intracellular cAMP levels rapidly dropped several-fold when wild type tight cell aggregates were disaggregated and remained low as the cells were cultured in the disaggregated state. Furthermore, overexpression of discoidin I mRNA late in development in EB-21 was corrected by addition of high concentrations of cAMP. These results are consistent with a second messenger function for cAMP in the contact-mediated regulatory response, and they indicate that the cAMP response machinery for discoidin I gene expression is capable of functioning in the cohesion-defective EB-21 strain.

B lymphocyte markers in multiple myeloma and related plasma cell dyscrasias.

Multiple myeloma and benign monoclonal gammopathies are regarded as monoclonal B cell proliferations in which B lymphocyte maturation is blocked in the final stages of the differentiation cycle. "Blocked" cells accumulate in the body and produce large quantities of immunoglobulins. These are monoclonal, because they come from a monoclonal cell stock. This study presents the results of peripheral B lymphocyte and marrow plasma cell typing designed to reveal the postulated isotypical relationship of the proliferating cells and the serum paraprotein. A good, though not absolute correlation between the two immunoglobulins was noted in most patients. The data, however, was not used in the diagnosis and treatment of these diseases. Further studies with MoAb's will, perhaps, provide a finer subclassification of the B lymphocyte proliferation diseases and assist in their diagnosis and treatment.