Search PubMed⌕ Search

Biomedical subjects

P Early

Publications and source records attributed to P Early.

71 records · Page 4Linked to original sources
PubMed1982

Immunoglobulin gene rearrangements in normal mouse B cells.

We have analyzed the structure of rearranged mu heavy-chain genes obtained from the genomic DNA of normal BALB/c mouse spleen cells expressing surface immunoglobulin M. Examples were found of two types of nonproductive rearrangements, which may be responsible for allelic exclusion in normal B cells. In one of these rearrangements, a germ line D gene segment has joined to the JH4 gene segment but no V/D joining has occurred. We present evidence that D gene segments lie as a cluster between V and J gene segments in the germ line. A comparison of conserved sequences in V and D gene segments suggests that the D gene segments, which are found only in the heavy-chain gene family, may have evolved from V gene segments similar to the Vk family.

Animals↗
PubMed1981

Expression of IgD may use both DNA rearrangement and RNA splicing mechanisms.

From a library of mouse sperm DNA, we have isolated two overlapping clones which contain the C(delta) gene. One of these clones also contains the C(mu) gene. The C(delta) gene is separated from the C(mu) membrane exons by approximately 2 kilobases (kb) of DAN. The C(delta) gene was identified by (a) hybridization to poly(A)(+)RNA prepared from the IgD-producing rat plasma cell tumor IR731, and (b) homology of a translated nucleotide sequence to the amino acid sequence of the human delta chain. The C(delta) gene spans 8 kb of DNA in the germ line. Plasmid subclones of the C(delta) gene were used as probes in Southern and RNA blot experiments. RNA blot analysis of cytoplasmic poly(A)(+)RNA from IR731 and a mu(+)delta(+) B-cell hybridoma revealed 1.6- and 2.7-kb delta mRNA species with different 3' ends, which presumably encode the secreted and membrane-bound forms, respectively, of the delta chain. Southern blot analysis of DNA from two mu(+)delta(+) lymphomas revealed that the C(delta) gene is in the germ-line configuration in each case. Restriction map analysis of C(mu) and C(delta) genomic clones isolated from a library of normal mu(+)delta(+) B-cell DNA also gave no evidence for DNA rearrangement in the region between the C(mu) and C(delta) genes. Taken together, these data suggest that IgD expression in mu(+)delta(+) B cells does not involve a V(H)-to-C(delta) DNA switch rearrangement. We propose that simultaneous expression of C(delta) and C(delta) with a single V(H) gene is mediated by two alternative routes of RNA processing of a primary nuclear transcript which contains the V(H), C(mu), and C(delta) genes. In contrast, analogous experiments with myeloma IR731 DNA revealed that the C(mu) gene has been deleted from the myeloma DNA and that the C(delta) gene has undergone DNA rearrangement, presumably including a switch recombination of the V(H) gene from the C(mu) to the C(delta) gene. These results indicate that two alternative mechanisms may be used in the expression of IgD molecules-RNA splicing in B cells and DNA rearrangement in plasma cells.

Animals↗
PubMed1980

Mouse Cmu heavy chain immunoglobulin gene segment contains three intervening sequences separating domains.

The IgM molecule is composed of subunits made up of two light chain and two heavy chain (mu) polypeptides. The mu chain is encoded by several gene segments--variable (V), joining (J) and constant (Cmu). The Cmu gene segment is of particular interest for several reasons. First, the mu chain must exist in two very different environments--as an integral membrane protein in receptor IgM molecules (micrometer) and as soluble serum protein in IgM molecules into the blood (mus). Second, the Cmu region in mus is composed of four homology units or domains (Cmu1, Cmu2, Cmu3 and Cmu4) of approximately 110 amino acid residues plus a C-terminal tail of 19 residues. We asked two questions concerning the organisation of the Cmu gene segment. (1) Are the homology units separated by intervening DNA sequences as has been reported for alpha (ref. 5), gamma 1 (ref. 6) and gamma 2b (ref. 7) heavy chain genes? (2) Is the C-terminal tail separated from the Cmu4 domain by an intervening DNA sequence? If so, DNA rearrangements or RNA splicing could generate hydrophilic and hydrophobic C-terminal tails for the mus and micrometer polypeptides, respectively. We demonstrate here that intervening DNA sequences separate each of the four coding regions for Cmu domains, and that the coding regions for the Cmu4 domains and the C-terminal tail are directly contiguous.

Animals↗
PubMed1980

An immunoglobulin heavy chain variable region gene is generated from three segments of DNA: VH, D and JH.

We have determined the sequences of separate germline genetic elements which encode two parts of a mouse immunglobulin heavy chain variable region. These elements, termed gene segments, are heavy chain counterparts of the variable (V) and joining (J) gene segments of immunoglobulin light chains. The VH gene segment encodes amino acids 1-101 and the JH gene segment encodes amino acids 107-123 of the S107 phosphorylcholine-binding VH region. This JH gene segment and two other JH gene segments are located 5' to the mu constant region gene (Cmu) in germline DNA. We have also determined the sequence of a rearranged VH gene encoding a complete VH region, M603, which is closely related to S107. In addition, we have partially determined the VH coding sequences of the S107 and M167 heavy chain mRNAs. By comparing these sequences to the germline gene segments, we conclude that the germline VH and JH gene segments do not contain at least 13 nucleotides which are present in the rearranged VH genes. In S107, these nucleotides encode amino acids 102-106, which form part of the third hypervariable region and consequently influence the antigen-binding specificity of the immunoglobulin molecule. This portion of the variable region may be encoded by a separate germline gene segment which can be joined to the VH and JH gene segments. We term this postulated genetic element the D gene segment, referring to its role in the generation of heavy chain diversity. Essentially the same noncoding sequences are found 3' to the VH gene segment and as inverse complements 5' to two JH gene segments. These are the same conserved nucleotides previously found adjacent to light chain V and J gene segments. Each conserved sequence consists of blocks of seven and ten conserved nucleotides which are separated by a spacer of either 11 or 22 nonconserved nucleotides. The highly conserved spacing, corresponding to one or two turns of the DNA helix, maintains precise spatial orientations between blocks of conserved nucleotides. Gene segments which can join to one another (VK and JK, for example) always have spacers of different lengths. Based on these observations, we propose a model for variable region gene rearrangement mediated by proteins which recognize the same conserved sequences adjacent to both light and heavy chain immunoglobulin gene segments.

Animals↗
PubMed1980

Two mRNAs with different 3' ends encode membrane-bound and secreted forms of immunoglobulin mu chain.

During differentiation, B lymphocytes undergo a shift from expression of membrane-bound IgM to IgM secretion. The mu chains of membrane and secreted IgM, mum and mus, respectively, differ in the amino acid sequence of their carboxy terminal regions. In this paper, we demonstrate that mum and mus heavy chains are encoded by separate mRNAs of 2.7 and 2.4 kb, respectively. Restriction mapping and sequence analysis of mu cDNA clones from a myeloma tumor that produces both types of mu chain indicate that the mum and mus mRNAs are identical throughout the coding region up to the 3' end of the fourth constant region (Cmu 4) domain, but differ in their C terminal coding and 3' untranslated segments. From the nucleotide sequence of the mum cDNA clone, we predict the amino acid sequence of the 41-residue mum C terminal segment or "M" (membrane) segment. This sequence has characteristics consistent with its being a transmembrane peptide. Thus the mus chain has a 20-residue hydrophilic C terminal segment after the Cmu 4 domain, and the mum chain has a 41-residue C terminal segment containing a hydrophobic sequence. We propose that comparable C terminal segments also will be found in other membrane-bound immunoglobulin heavy chains.

Animals↗
PubMed1980

Organization of kappa light chain genes in germ-line and somatic tissue.

We studied the organization of the kappa light chain genes in germ-line (sperm) and somatic (embryo) tissues. We constructed a plasmid containing a DNA insert coding for the kappa chain MOPC 167 and used the Southern blotting technique to determine the organization of kappa variable and constant region genes. In the haploid genome of the mouse there is only one constant region gene detectable and it has the same organization in sperm and embryo DNAs. There are several variable region genes in sperm and embryo that are related to the Vk167 gene. The organization of the V genes in sperm and embryo DNAs is identical. These results show that there is no rearrangement of variable region genes (or "minigenes") during early embryogenesis.

Alleles↗