have formed a joint venture with shared ownership and governance of Baylor Genetics (BG), which performs clinical microarray analysis and clinical exome sequencing. JRL serves on the scientific advisory board of BG. JRL has stock ownership in 23andMe, is a paid consultant for Regeneron Pharmaceuticals, and is a coinventor on multiple US and European patents related to molecular diagnostics for inherited neuropathies, eye diseases, and bacterial genomic fingerprinting (

Cytomegalovirus (CMV) subunit vaccine candidates include glycoprotein B (gB), and phosphoprotein ppUL83 (pp65). Using a guinea pig cytomegalovirus (GPCMV) model, this study compared immunogenicity, pregnancy outcome, and congenital viral infection following pre-pregnancy immunization with a three-dose series of modified vaccinia virus Ankara (MVA)- vectored vaccines consisting either of gB administered alone, or simultaneously with a pp65 homolog (GP83)-expressing vaccine. Vaccinated and control dams were challenged at midgestation with salivary gland-adapted GPCMV. Comparisons included ELISA and neutralizing antibody responses, maternal viral load, pup mortality, and congenital infection rates. Strikingly, ELISA and neutralization titers were significantly lower in the gB/GP83 combined vaccine group than in the gB group. However, both vaccines protected against pup mortality (60.5% in controls vs. 11.4% and 8.3% in gB and gB/GP83 combination groups, respectively; p<0.0001). Reductions in pup viral load were noted for both groups compared to control, but preconception vaccine resulted in a significant reduction in GPCMV transmission in the monovalent gB group only (26/44, 59 % v. 27/34, 79 % in controls; p<0.05). We conclude that, in the MVA platform, adding GP83 to a gB subunit vaccine interferes with antibody responses and diminishes protection against congenital GPCMV infection, but does not decrease protection against pup mortality.

Minichromosome maintenance protein 10 (MCM10) is essential for eukaryotic DNA replication. Here, we describe compound heterozygous MCM10 variants in patients with distinctive, but overlapping, clinical phenotypes: natural killer (NK) cell deficiency (NKD) and restrictive cardiomyopathy (RCM) with hypoplasia of the spleen and thymus. To understand the mechanism of MCM10-associated disease, we modeled these variants in human cell lines. MCM10 deficiency causes chronic replication stress that reduces cell viability due to increased genomic instability and telomere erosion. Our data suggest that loss of MCM10 function constrains telomerase activity by accumulating abnormal replication fork structures enriched with single-stranded DNA. Terminally-arrested replication forks in MCM10-deficient cells require endonucleolytic processing by MUS81, as MCM10:MUS81 double mutants display decreased viability and accelerated telomere shortening. We propose that these bi-allelic variants in MCM10 predispose specific cardiac and immune cell lineages to prematurely arrest during differentiation, causing the clinical phenotypes observed in both NKD and RCM patients.

Deoxyribonucleic acid (DNA) replication can be divided into three major steps: initiation, elongation and termination. Each time a human cell divides, these steps must be reiteratively carried out. Disruption of DNA replication can lead to genomic instability, with the accumulation of point mutations or larger chromosomal anomalies such as rearrangements. While cancer is the most common class of disease associated with genomic instability, several congenital diseases with dysfunctional DNA replication give rise to similar DNA alterations. In this review, we discuss all congenital diseases that arise from pathogenic variants in essential replication genes across the spectrum of aberrant replisome assembly, origin activation and DNA synthesis. For each of these conditions, we describe their clinical phenotypes as well as molecular studies aimed at determining the functional mechanisms of disease, including the assessment of genomic stability. By comparing and contrasting these diseases, we hope to illuminate how the disruption of DNA replication at distinct steps affects human health in a surprisingly cell-type-specific manner.

Minichromosome maintenance protein 10 (Mcm10) is essential for eukaryotic DNA replication initiation and fork stability. Recently, a compound heterozygous MCM10 mutation was identified in a patient who presented with natural killer (NK) cell deficiency.To understand the mechanism of disease, we modeled this mutation in human cell lines.We demonstrate that Mcm10 deficiency causes chronic replication stress that reduces cell viability due to increased genomic instability and telomere maintenance defects.Our data suggests that Mcm10 deficiency constrains telomerase-dependent telomere extension. This limitation can be overcome by increasing telomerase activity, although defects in telomere replication persist. We propose that stalled replication forks in Mcm10-deficient cells arrest terminally, especially within hard-to-replicate regions, and require nuclease processing involving Mus81, as MCM10:MUS81 double mutants displayed decreased viability and accelerated telomere erosion. Our results reveal that Mcm10 is critical for telomere replication and provide insights into how MCM10 mutations cause NK cell deficiency.

Double strand DNA break repair (DSBR) comprises multiple pathways. A subset of DSBR pathways, including single strand annealing, involve intermediates with 3′ non-homologous tails that must be removed to complete repair. In Saccharomyces cerevisiae, Rad1–Rad10 is the structure-specific endonuclease that cleaves the tails in 3′ non-homologous tail removal (3′ NHTR). Rad1–Rad10 is also an essential component of the nucleotide excision repair (NER) pathway. In both cases, Rad1–Rad10 requires protein partners for recruitment to the relevant DNA intermediate. Msh2–Msh3 and Saw1 recruit Rad1–Rad10 in 3′ NHTR; Rad14 recruits Rad1–Rad10 in NER. We created two rad1 separation-of-function alleles, rad1R203A,K205A and rad1R218A; both are defective in 3′ NHTR but functional in NER. In vitro, rad1R203A,K205A was impaired at multiple steps in 3′ NHTR. The rad1R218A in vivo phenotype resembles that of msh2- or msh3-deleted cells; recruitment of rad1R218A–Rad10 to recombination intermediates is defective. Interactions among rad1R218A–Rad10 and Msh2–Msh3 and Saw1 are altered and rad1R218A–Rad10 interactions with RPA are compromised. We propose a model in which Rad1–Rad10 is recruited and positioned at the recombination intermediate through interactions, between Saw1 and DNA, Rad1–Rad10 and Msh2–Msh3, Saw1 and Msh2–Msh3 and Rad1–Rad10 and RPA. When any of these interactions is altered, 3′ NHTR is impaired.

Human natural killer cell deficiency (NKD) arises from inborn errors of immunity that lead to impaired NK cell development, function or both. Through the understanding of the biological perturbations in individuals with NKD, requirements for the generation of terminally mature functional innate effector cells can be elucidated. Here we report a novel cause of NKD resulting from compound heterozygous mutations in MCM10 that impaired NK cell maturation in a child with fatal susceptibility to CMV. MCM10 has not been previously associated with monogenic disease and plays a critical role in the activation and function of the eukaryotic DNA replisome. By modeling MCM10 deficiency in human NK cell lines and primary NK cell precursors, we demonstrate that MCM10 is required for NK cell terminal maturation and acquisition of immunological system function. cytotoxicity | natural killer cell | NK cell deficiency | primary immunodeficiency

Natural killer cell deficiency (NKD) is a rare disease in which natural killer (NK) cell function is reduced, leaving affected individuals susceptible to repeated viral infections and cancer. Defects in several replication factors have been shown to cause a class of NKD that has complete loss of mature NK cells. Recently, a new NKD patient was identified with a compound heterozygous mutation in MCM10 (minichromosome maintenance 10), an essential gene required for DNA replication. In this patient, one allele contains a missense mutation of a highly conserved residue and the other has a nonsense mutation causing loss of function. To better understand how each mutation affects DNA replication, we generated MCM10 heterozygous HCT116 and hTERT‐RPE1 cell lines, mimicking the nonsense mutation in transformed and nontransformed cells. Analysis of these cell lines demonstrated that MCM10 was haploinsufficient, resulting in increased doubling time, enhanced sensitivity to genotoxic drugs, and reduced viability. Although the nonsense mutation was haploinsufficient in cellular systems, the patient inherited this allele from a healthy parent implying that the missense mutation is contributing to the clinical phenotype. Consistent with this notion, hTERT‐RPE1 cells homozygous for the missense mutation also displayed an increase in doubling time. These data suggested that the compound heterozygous MCM10 mutation led to loss of functionally mature NK cells due to reduced proliferative capacity. To better understand the molecular defects underlying the observed phenotypes, we further analyzed the heterozygous HCT116 mutants. Cell cycle analysis demonstrated delay in mitotic progression, but a relatively normal cell cycle distribution. Moreover, we observed defects in replication initiation and decreased replication fork restart following induction of fork stalling. Interestingly, these defects in DNA replication did not cause acute DNA damage suggesting that MCM10 haploinsufficiency led to minor defects in global DNA replication that remained below the threshold of checkpoint activation. Rather, the observed reduction in viability was associated with increased genomic instability over time including progressive telomere erosion. To uncover the molecular mechanisms of telomere shortening, we utilized 2D gel analyses which showed increased accumulation of telomeric “t‐complexes” in MCM10 mutants. This high molecular weight species consist of highly branched DNAs with single‐stranded regions that may result from stalled replication forks. Taken together, these data suggest that replication defects caused by MCM10 deficiency are exacerbated in hard‐to‐replicate, origin poor regions such as telomeres and cause replicative exhaustion. Currently, we are determining whether telomere erosion driven by MCM10 depletion prevents development of mature NK cells.Support or Funding InformationSupported by NIH R01 GM074917.This abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.