Pilot studies in human populations have demonstrated a correlation between the level of antigen receptor trans-rearrangements and risk (at the population level) of lymphoid malignancy, Irradiation of newborn severe combined immune deficiency mice results in an increased risk of subsequent development of thymic lymphoma (100% of mice so irradiated are dead of thymic lymphoma by 20 weeks of age), We, therefore, assayed the occurrence of trans-rearrangements in this well-controlled mouse mutant system and found a 50-100-fold increase in the absolute number of TCRGV-TCRBJ trans-rearrangements compared to unirradiated litter-mates (and a comparable fold increase over age-matched BALB/c mice) at 2 weeks following irradiation, We also found a marked disproportion in generating trans-rearrangements versus intralocus rearrangements in the severe combined immune deficiency system compared to BALB/c, independent of irradiation. The trans-rearrangements noted were polyclonal in nature, These data, again, suggest that the absolute level of antigen receptor trans-rearrangements may serve as a biomarker of lymphoma risk.

We report here the molecular cloning and chromosomal localization of an additional member of the helix-loop-helix (HLH) family of transcription factors, NSCL. The NSCL gene was identified based on its hybridization to the previously described hemopoietic HLH gene, SCL. Murine NSCL cDNA clones were obtained from a day 11.5 mouse embryo cDNA library. The coding region is 399 base pairs and encodes a predicted protein of 14.8 kDa. The nucleotide sequence shows 71% identity and the amino acid sequence shows 61% identity to murine SCL in the HLH domain. The NSCL protein-coding region terminates six amino acids beyond the second amphipathic helix of the HLH domain. Expression of NSCL was detected in RNA from mouse embryos between 9.5 and 14.5 days postcoitus, with maximum levels of expression at 10.5-12 days. Examination of 12- and 13-day mouse embryos by in situ hybridization revealed expression of NSCL in the developing nervous system. The NSCL gene was mapped to murine chromosome 1. The very restricted pattern of NSCL expression suggests an important role for this HLH protein in neurological development.

We describe the structural organization of the human SCL gene, a helix-loop-helix family member which we believe plays a fundamental role in hematopoietic differentiation. The SCL locus is composed of eight exons distributed over 16 kb. SCL shows a pattern of expression quite restricted to early hematopoietic tissues, although in malignant states expression of the gene may be somewhat extended into later developmental stages. A detailed analysis of the transcript(s) arising from the SCL locus revealed that (i) the 5' noncoding portion of the SCL transcript, which resides within a CpG island, has a complex pattern of alternative exon utilization as well as two distinct transcription initiation sites; (ii) the 5' portions of the SCL transcript contain features that suggest a possible regulatory role for these segments; (iii) the pattern of utilization of the 5' exons is cell lineage dependent; and (iv) all of the currently studied chromosomal aberrations that affect the SCL locus either structurally or functionally eliminate the normal 5' transcription initiation sites. These data suggest that the SCL gene, and specifically its 5' region, may be a target for regulatory interactions during early hematopoietic development.

We describe a t(14;14)(q11;q32) translocation in a patient with T-cell chronic lymphocytic leukemia and ataxia-telangiectasia (AT). By using a battery of joining (J)-segment probes from the T-cell receptor (TCR) alpha-chain locus TCRA, three distinct J alpha rearrangements were observed. One rearrangement reflected a normal TCRA variable (V) region V alpha-to-J alpha recombination. The second rearrangement was caused by the translocation even itself, which joined a DNA segment from 14q32 centromeric to the immunoglobulin heavy chain locus (IGH) and a J alpha gene located approximately 75 kilobases (kb) 5' of the TCRA constant region gene (C alpha). A third rearrangement involved a 17-kb internal deletion 3' to the translocation, a rearrangement within the J alpha locus that has been observed once before in a patient with AT. Analysis of these three rearrangements underscores the increase in aberrant locus-specific recombination in lymphocytes from patients with AT. Furthermore, these studies support the view that a growth-effecting gene is present in the 14q32 region that participates in the leukemogenic process.

A complex translocation has interrupted the third exon of the c-myc gene in human plasma cell myeloma tumor cells and a derivative cell line (NCI-H929). As a result of this rearrangement, a chimeric mRNA is expressed which commences 5' of the c-myc coding region and includes sequences introduced by the translocation event. All of the detectable c-myc-containing mRNA in the tumor and cell line was derived from this rearranged c-myc allele. This chimeric c-myc mRNA, in which most of the germ line c-myc 3' untranslated region has been replaced, was greater than sevenfold more stable than c-myc transcripts with intact 3' ends. This suggests that the 3' untranslated region may play an important role in c-myc mRNA stability.

The structural gene for galactosyltransferase (glycoprotein 4-B-galactosyltransferase, EC 2.4.1.38) was localized to human chromosome 9 band p13 by chromosome in situ hybridization using a cloned bovine galactosyltransferase cDNA probe. This chromosomal location is at the same position to which galactose-1-phosphate uridyltransferase, an enzyme which provides the nucleotide sugar substrate (UDP-galactose) for galactosyltransferase, has been mapped.

We have investigated the expression of the genes c-myb, c-myc, and alpha globin in murine erythroid cells at different stages of development, in viral-induced erythroleukemias, as well as in two mouse erythroleukemia cell lines that can be induced to terminally differentiate when exposed to dimethylsulfoxide. We find that there is a reciprocal correlation between the cell's production of messenger RNA for c-myb and globin. c-myc message shows a similar but less dramatic decrease coincident with globin RNA production. Initially with the administration of an inducing agent, dimethylsulfoxide, there is a rapid decrease of myc and myb mRNA, which is followed by signs of differentiation in the induced culture. We conclude that these oncogenes function in early maturational stages of development of these cells. In the erythroleukemic state these genes are down-regulated by forced differentiation and may play a direct role in influencing the state of differentiation of these cells.

A cDNA clone encoding the alpha chain of the human T cell receptor was used in connection with somatic cell human-rodent hybrids to determine that the genes coding for the alpha chain are located on chromosome 14 in humans. In situ hybridization confirms this result and further localizes these genes to 14q11-14q12 on this chromosome. Since this region of chromosome has been shown to be nonrandomly involved in a number of T cell neoplasias, this assignment raises a number of interesting questions as to the possible involvement of the T cell receptor alpha chain genes in tumorigenesis.

The ability to detect immunoglobulin-gene rearrangements has proved useful in confirming diagnoses of suspected B-cell lymphomas and in establishing their monoclonality. By analogy, we employed a cloned DNA probe for the beta chain of the T-cell receptor gene to determine whether gene rearrangements were present in human T-cell neoplasms representing various stages of T-cell development. Gene rearrangements were present in all cases of T-cell disorders except a single case of T gamma lymphocytosis, a disorder that has not been proved to be a clonal T-cell neoplasm. A germline gene configuration was present in all patients with non-T-cell neoplasms and in normal tissues from patients with T-cell lymphoma. The probe promises to be useful for confirming the pathological an immunologic diagnosis in difficult cases of T-cell disorders and for assessing the extent of disease.