A global survey of haplotype frequencies and linkage disequilibrium at the DRD2 locus

A four-site haplotype system at the dopamine D2 receptor locus (DRD2) has been studied in a global sample of 28 distinct populations. The haplotype system spans about 25 kb, encompassing the coding region of the gene. The four individual markers include three TaqI restriction site polymorphisms (RSPs) – TaqI “A”, “B”, and “D” sites – and one dinucleotide short tandem repeat polymorphism (STRP). All four of the marker systems are polymorphic in all regions of the world and in most individual populations. The haplotype system shows the highest average heterozygosity in Africa, a slightly lower average heterozygosity in Europe, and the lowest average heterozygosities in East Asia and the Americas. Across all populations, 20 of the 48 possible haplotypes reached a frequency of at least 5% in at least one population sample. However, no single population had more than six haplotypes reaching that frequency. In general, African populations had more haplotypes present in each population and more haplotypes occurring at a frequency of at least 5% in that population. Permutation tests for significance of overall disequilibrium (all sites considered simultaneously) were highly significant (P<0.001) in all 28 populations. Except for three African samples, the pairwise disequilibrium between the outermost RSP markers, TaqI “B” and “A”, was highly significant with D’ values greater than 0.8; in two of those exceptions the RSP marker was not polymorphic. Except for those same two African populations, the 16-repeat allele at the STRP also showed highly significant disequilibrium with the TaqI “B” site in all populations, with D’ values usually greater than 0.7. Only four haplotypes account for more than 70% of all chromosomes in virtually all non-African populations, and two of those haplotypes account for more than 70% of all chromosomes in most East Asian and Amerindian populations. A new measure of the amount of overall disequilibrium shows least disequilibrium in African populations, somewhat more in European populations, and the greatest amount in East Asian and Amerindian populations. This pattern seems best explained by random genetic drift with low levels of recombination, a low mutation rate at the STRP, and essentially no recurrent mutation at the RSP sites, all in conjunction with an “Out of Africa” model for recent human evolution. Received: 14 January 1998 / Accepted 19 March 1998     

HUWE1 interacts with PCNA to alleviate replication stress

Defects in DNA replication, DNA damage response, and DNA repair compromise genomic stability and promote cancer development. In particular, unrepaired DNA lesions can arrest the progression of the DNA replication machinery during S‐phase, causing replication stress, mutations, and DNA breaks. HUWE1 is a HECT‐type ubiquitin ligase that targets proteins involved in cell fate, survival, and differentiation. Here, we report that HUWE1 is essential for genomic stability, by promoting replication of damaged DNA. We show that HUWE1‐knockout cells are unable to mitigate replication stress, resulting in replication defects and DNA breakage. Importantly, we find that this novel role of HUWE1 requires its interaction with the replication factor PCNA, a master regulator of replication fork restart, at stalled replication forks. Finally, we provide evidence that HUWE1 mono‐ubiquitinates H2AX to promote signaling at stalled forks. Altogether, our work identifies HUWE1 as a novel regulator of the replication stress response.     

DEXTRANS AND GLYCOGENS AS PARTICULATE TRACERS FOR STUDYING CAPILLARY PERMEABILITY

Commercially available glycogens and dextrans can be used as biological particulate tracers in work on capillary permeability. These polysaccharides are well tolerated in intravenous injection and induce no vascular leakage when applied topically (cremaster test) in mice and in Wistar-Furth rats. The particles stain adequately with lead after aldehyde-OsO₄ fixation in phosphate buffer and provide a relatively wide set of probes (~45 A-300 A) for work on the large and small pore systems.     

Dominant-negative TLR5 polymorphism reduces adaptive immune response to flagellin and negatively associates with Crohn's disease

Crohn's disease (CD) is associated with elevated adaptive immunity to commensal microbes, with flagellin being a dominant antigen. In light of heightened awareness of the importance of innate immunity in regulating adaptive immunity and ambiguity as to the role of CD-associated immune responses in CD pathophysiology, we sought to determine whether natural acquisition of immune responses to flagellin were regulated by the innate immune flagellin receptor toll-like receptor 5 (TLR5) and determine whether persons carrying a recently defined common dominant-negative TLR5 polymorphism (TLR5-stop) might be protected from developing CD. Carriage rates of a recently defined dominant-negative TLR5 polymorphism (TLR5-stop) and levels of serum immunoreactivity to bacterial products were measured in inflammatory bowel disease patients, first-degree relatives, and unrelated controls. We observed that, in healthy subjects, persons carrying TLR5-stop had significantly lower levels of flagellin-specific IgG and IgA but had similar levels of total and LPS-specific Ig. Moreover, we observed that, among Jewish subjects, the carriage rate of TLR5-stop (in heterozygous state) was significantly less in CD patients, but not ulcerative colitis (UC) patients, compared with unaffected relatives and unrelated controls (5.4, 0.9, 6.0, and 6.5% for unaffected relatives, CD, UC, and unrelated Jewish controls, respectively, n = 296, 215, 185, and 416, respectively; P = 0.037 by likelihood calculation for CD vs. controls), indicating that TLR5-stop can protect persons of Jewish ethnicity against CD. We did not observe a significant association of TLR5-stop with CD in a non-Jewish cohort (11.1, 10.4, and 11.7% for unaffected relatives, CD, and UC, respectively; n = 841, 543, and 300 for unaffected relatives, respectively). These results demonstrate that natural acquisition of immune responses to flagellin are regulated by TLR5 and suggest that immune responses to flagellin are not merely associated with CD but rather promote the pathogenic response.     

Synthesis and structural characterization of gold(III) dioximates with anions [AuCl4] and [AuCl2]

Two complexes of Au(III) with dimethylglyoxime of compositions [Au^III(HDMG)₂][Au^IIICl₄] (1) and [Au^III(HDMG)₂][Au^ICl₂] (2) were synthesized and characterized by X-ray structural analysis. It was shown that in [Au^III(HDMG)₂]⁺ cation Au(III) has a square-planar environment, and the oxygen atoms of oxime groups are joined by intramolecular H-bond. The secondary Au?Au and Au?Cl interactions in the crystal are discussed.     

Somatic hypermutation and class switch recombination in Msh6(-/-)Ung(-/-) double-knockout mice

Somatic hypermutation (SHM) and class switch recombination (CSR) are initiated by activation-induced cytosine deaminase (AID). The uracil, and potentially neighboring bases, are processed by error-prone base excision repair and mismatch repair. Deficiencies in Ung, Msh2, or Msh6 affect SHM and CSR. To determine whether Msh2/Msh6 complexes which recognize single-base mismatches and loops were the only mismatch-recognition complexes required for SHM and CSR, we analyzed these processes in Msh6(-/-)Ung(-/-) mice. SHM and CSR were affected in the same degree and fashion as in Msh2(-/-)Ung(-/-) mice; mutations were mostly C,G transitions and CSR was greatly reduced, making Msh2/Msh3 contributions unlikely. Inactivating Ung alone reduced mutations from A and T, suggesting that, depending on the DNA sequence, varying proportions of A,T mutations arise by error-prone long-patch base excision repair. Further, in Msh6(-/-)Ung(-/-) mice the 5' end and the 3' region of Ig genes was spared from mutations as in wild-type mice, confirming that AID does not act in these regions. Finally, because in the absence of both Ung and Msh6, transition mutations from C and G likely are "footprints" of AID, the data show that the activity of AID is restricted drastically in vivo compared with AID in cell-free assays.