Molecular genetic study of human arginase deficiency

We have explored the molecular pathology in 28 individuals homozygous or heterozygous for liver arginase deficiency (hyperargininemia) by a combination of Southern analysis, western blotting, DNA sequencing, and PCR. This cohort represents the majority of arginase-deficient individuals worldwide. Only 2 of 15 homozygous patients on whom red blood cells were available had antigenically cross-reacting material as ascertained by western blot analysis using anti-liver arginase antibody. Southern blots of patient genomic DNAs, cut with a variety of restriction enzymes and probed with a near-full-length (1,450-bp) human liver arginase cDNA clone, detected no gross gene deletions. Loss of a TaqI cleavage site was identified in three individuals: in a homozygous state in a Saudi Arabian patient at one site, at a different site in homozygosity in a German patient, and in heterozygosity in a patient from Australia. The changes in the latter two were localized to exon 8, through amplification of this region by PCR and electrophoretic analysis of the amplified fragment after treatment with TaqI; the precise base changes (Arg291X and Thr290Ser) were confirmed by sequencing. It is interesting that the latter nucleotide variant (Thr290Ser) was found to lie adjacent to the TaqI site rather than within it, though whether such a conservative amino acid substitution represents a true pathologic mutation remains to be determined. We conclude that arginase deficiency, though rare, is a heterogeneous disorder at the genotypic level, generally encompassing a variety of point mutations rather than substantial structural gene deletions.     

Cutting Edge: Multiple autoimmune pathways in kd/kd mice

The kidney disease (kd) mutation was transferred to a C57BL/6 (B6) background by selection for closely linked microsatellite markers. The resulting congenic strain, B6.kd, was mated with partners homozygous for targeted mutations of CD4, CD8, CD28, IL-2, recombinase-activating gene-1 (Rag-1), ICAM-1, or beta(2)-microglobulin. In most of the resulting double mutants, kidney disease occurred as readily and as severely as in the B6.kd controls, although disease occurred somewhat less frequently in age-matched CD28(-/-) kd/kd mice. Immunohistology demonstrated a predominance of macrophages in the lesions of B6.kd and most of the double mutants, with the remaining cells consisting of T cells and variable numbers of NK cells. In Rag-1(-/-) kd/kd, approximately 50% of infiltrating cells were macrophages, and approximately 50% were NK cells. These results suggest that the initial lesion caused by the mutant gene is intrinsic to the kidney and that the immune response that subsequently occurs can involve any one of several different cellular compositions.     

Molecular assays for detecting Aphanomyces invadans in ulcerative mycotic fish lesions

The pathogenic oomycete Aphanomyces invadans is the primary etiological agent in ulcerative mycosis, an ulcerative skin disease caused by a fungus-like agent of wild and cultured fish. We developed sensitive PCR and fluorescent peptide nucleic acid in situ hybridization (FISH) assays to detect A. invadans. Laboratory-challenged killifish (Fundulus heteroclitus) were first tested to optimize and validate the assays. Skin ulcers of Atlantic menhaden (Brevoortia tyrannus) from populations found in the Pamlico and Neuse River estuaries in North Carolina were then surveyed. Results from both assays indicated that all of the lesioned menhaden (n = 50) collected in September 2004 were positive for A. invadans. Neither the FISH assay nor the PCR assay cross-reacted with other closely related oomycetes. These results provided strong evidence that A. invadans is the primary oomycete pathogen in ulcerative mycosis and demonstrated the utility of the assays. The FISH assay is the first molecular assay to provide unambiguous visual confirmation that hyphae in the ulcerated lesions were exclusively A. invadans.     

Double trouble—Buffer selection and His-tag presence may be responsible for nonreproducibility of biomedical experiments

The availability of purified and active protein is the starting point for the majority of in vitro biomedical, biochemical, and drug discovery experiments. The use of polyhistidine affinity tags has resulted in great increases of the efficiency of the protein purification process, but can negatively affect structure and/or activity measurements. Similarly, buffer molecules may perturb the conformational stability of a protein or its activity. During the determination of the structure of a Gcn5-related N-acetyltransferase (GNAT) from Pseudomonas aeruginosa (PA4794), we found that both HEPES and the polyhistidine affinity tag bind (separately) in the substrate-binding site. In the case of HEPES, the molecule induces conformational changes in the active site, but does not significantly affect enzyme activity. In contrast, the uncleaved His-tag does not induce major conformational changes but acts as a weak competitive inhibitor of peptide substrate. In two other GNAT enzymes, we observed that the presence of the His-tag had a strong influence on the activity of these proteins. The influence of protein preparation on functional studies may affect the reproducibility of experiments in other laboratories, even when changes between protocols seem at first glance to be insignificant. Moreover, the results presented here show how critical it is to adjust the experimental conditions for each protein or family of proteins, and investigate the influence of these factors on protein activity and structure, as they may significantly alter the effectiveness of functional characterization and screening methods. Thus, we show that a polyhistidine tag and the buffer molecule HEPES bind in the substrate-binding site and influence the conformation of the active site and the activity of GNAT acetyltransferases. We believe that such discrepancies can influence the reproducibility of some experiments and therefore could have a significant “ripple effect” on subsequent studies.     

Deep sequencing reveals clonal evolution patterns and mutation events associated with relapse in B-cell lymphomas

Background

Molecular mechanisms associated with frequent relapse of diffuse large B-cell lymphoma (DLBCL) are poorly defined. It is especially unclear how primary tumor clonal heterogeneity contributes to relapse. Here, we explore unique features of B-cell lymphomas - VDJ recombination and somatic hypermutation - to address this question.

Results

We performed high-throughput sequencing of rearranged VDJ junctions in 14 pairs of matched diagnosis-relapse tumors, among which 7 pairs were further characterized by exome sequencing. We identify two distinctive modes of clonal evolution of DLBCL relapse: an early-divergent mode in which clonally related diagnosis and relapse tumors diverged early and developed in parallel; and a late-divergent mode in which relapse tumors developed directly from diagnosis tumors with minor divergence. By examining mutation patterns in the context of phylogenetic information provided by VDJ junctions, we identified mutations in epigenetic modifiers such as KMT2D as potential early driving events in lymphomagenesis and immune escape alterations as relapse-associated events.

Conclusions

Altogether, our study for the first time provides important evidence that DLBCL relapse may result from multiple, distinct tumor evolutionary mechanisms, providing rationale for therapies for each mechanism. Moreover, this study highlights the urgent need to understand the driving roles of epigenetic modifier mutations in lymphomagenesis, and immune surveillance factor genetic lesions in relapse.

Electronic supplementary material

The online version of this article (doi:10.1186/s13059-014-0432-0) contains supplementary material, which is available to authorized users.