Molecular analysis of membrane immunoglobulin-negative variants.

The mouse B-cell lymphoma WEHI 279.1 is a tumor which synthesizes both membrane and secreted immunoglobulin M (IgM). We have immunoselected variants which fail to express the membrane form (mIgM-); the most frequently isolated phenotype is a complete loss of both membrane expression and synthesis of the mu heavy chain within the cells. We have chosen four of these mIgM- mutants for detailed molecular investigation. One of these has suffered a large deletion which covers the region of chromosome 12 containing the expressed mu gene, but three have no detectable changes in the DNA arrangement of the mu gene. All of the mutants, including the deletion mutant, synthesize 10-30% of the wild-type level of cytoplasmic mu RNA; however, none is the appropriate size for membrane mu (mu m) or secreted mu (mu s) message. Based on our studies of the deletion mutant, which retains its nonproductively arranged allele, at least some of these RNAs may be 'sterile' transcripts from the nonproductively arranged allele. However, if all of these mRNAs derive from the other allele, they represent a substantial elevation of these sterile messages relative to the wild-type level. Furthermore, the three nondeletion mutants transcribe mu RNA at a level indistinguishable from the wild type. It is likely that their defects lie in the stability, processing, or transport of the mu RNA within the nucleus. Somatic cell hybrids between P3X and the IgM- variants produced mostly mIgM- hybrids. However, a few mIgM+ hybrids were produced, suggesting that the mu- defects may be partly complemented by the P3X fusion partner.

Molecular organization of the decapentaplegic gene in Drosophila melanogaster.

The decapentaplegic (dpp) locus of Drosophila melanogaster is a greater than 55 kb genetic unit required for proper pattern formation during the embryonic and imaginal development of the organism. We have proposed that these morphogenetic functions result from the action of a secreted transforming growth factor-beta (TGF-beta)-related protein product encoded by dpp. In this paper we localize 60 mutations on the molecular map of dpp. The positions of these mutations cluster according to phenotypic class, identifying the locations of specific dpp functions. By Northern and cDNA analysis, we characterize five overlapping dpp transcripts. On the basis of the locations of the overlaps relative to a previously sequenced cDNA, it is likely that these transcripts all encode similar or identical polypeptides. We propose that the bulk of dpp DNA consists of extensive arrays of cis-regulatory information. The large (greater than 25-kb) 3' cis-regulatory region represents a novel feature of dpp gene organization