A De Novo Deletion in the Regulators of Complement Activation Cluster Producing a Hybrid Complement Factor H/Complement Factor H-Related 3 Gene in Atypical Hemolytic Uremic Syndrome.

The regulators of complement activation cluster at chromosome 1q32 contains the complement factor H (CFH) and five complement factor H-related (CFHR) genes. This area of the genome arose from several large genomic duplications, and these low-copy repeats can cause genome instability in this region. Genomic disorders affecting these genes have been described in atypical hemolytic uremic syndrome, arising commonly through nonallelic homologous recombination. We describe a novel CFH/CFHR3 hybrid gene secondary to a de novo 6.3-kb deletion that arose through microhomology-mediated end joining rather than nonallelic homologous recombination. We confirmed a transcript from this hybrid gene and showed a secreted protein product that lacks the recognition domain of factor H and exhibits impaired cell surface complement regulation. The fact that the formation of this hybrid gene arose as a de novo event suggests that this cluster is a dynamic area of the genome in which additional genomic disorders may arise.

Characterization of a factor H mutation that perturbs the alternative pathway of complement in a family with membranoproliferative GN.

Complement C3 activation is a characteristic finding in membranoproliferative GN (MPGN). This activation can be caused by immune complex deposition or an acquired or inherited defect in complement regulation. Deficiency of complement factor H has long been associated with MPGN. More recently, heterozygous genetic variants have been reported in sporadic cases of MPGN, although their functional significance has not been assessed. We describe a family with MPGN and acquired partial lipodystrophy. Although C3 nephritic factor was shown in family members with acquired partial lipodystrophy, it did not segregate with the renal phenotype. Genetic analysis revealed a novel heterozygous mutation in complement factor H (R83S) in addition to known risk polymorphisms carried by individuals with MPGN. Patients with MPGN had normal levels of factor H, and structural analysis of the mutant revealed only subtle alterations. However, functional analysis revealed profoundly reduced C3b binding, cofactor activity, and decay accelerating activity leading to loss of regulation of the alternative pathway. In summary, this family showed a confluence of common and rare functionally significant genetic risk factors causing disease. Data from our analysis of these factors highlight the role of the alternative pathway of complement in MPGN.

The microstratigraphy and depositional environments of Lida Ajer and Ngalau Gupin, two fossil-bearing tropical limestone caves of west Sumatra.

Lida Ajer and Ngalau Gupin are karstic caves situated in the Padang Highlands, western Sumatra, Indonesia. Lida Ajer is best known for yielding fossil evidence that places the arrival of Homo sapiens in Southeast Asia during Marine Isotope Stage 4, one of the earliest records for the region. Ngalau Gupin recently produced the first record of hippopotamid Hexaprotodon on the island, representing the only globally extinct taxon in Pleistocene deposits from Sumatra. Microstratigraphic (micromorphological) analyses were applied to unconsolidated fossil-bearing cave sediments from these two sites. We use micromorphology as part of a micro-contextualised taphonomic approach to identify the diagenetic processes affecting fossils and sediments within these caves, through phases of their depositional history. The fossil-bearing sediments in Lida Ajer have been subjected to a suite of natural sedimentation processes ranging from water action to carnivore occupation, which would indicate the fossils underwent significant reworking prior to lithification of the deposit. The results demonstrate that the base of the unconsolidated fossil-bearing sediments in Ngalau Gupin were derived from the interior of the cave, where the matrix was partially phosphatized as a result of guano-driven diagenesis. These observations can be used to test hypotheses about the integrity of incorporated vertebrate remains and to aid in local palaeoenvironmental reconstructions. The methods employed in this research have not previously been applied to cave sediments from sites in the Padang Highlands and provide key new insights into the palaeontological and natural history of the western region of Sumatra.

An arginase 2 promoter transgenic line illuminates immune cell polarisation in zebrafish.

Innate immune responses to inflammation and infection are complex and represent major challenges for developing much needed new treatments for chronic inflammatory diseases and drug-resistant infections. To be ultimately successful, the immune response must be balanced to allow pathogen clearance without excess tissue damage, processes controlled by pro- and anti-inflammatory signals. The roles of anti-inflammatory signalling in raising an appropriate immune response are underappreciated, representing overlooked potential drug targets. This is especially true in neutrophils, a difficult cell type to study ex vivo owing to a short lifespan, dogmatically seen as being highly pro-inflammatory. Here, we have generated and describe the first zebrafish transgenic line [TgBAC(arg2:eGFP)sh571] that labels expression of the anti-inflammatory gene arginase 2 (arg2) and show that a subpopulation of neutrophils upregulate arginase soon after immune challenge with injury and infection. At wound-healing stages, arg2:GFP is expressed in subsets of neutrophils and macrophages, potentially representing anti-inflammatory, polarised immune cell populations. Our findings identify nuanced responses to immune challenge in vivo, responses that represent new opportunities for therapeutic interventions during inflammation and infection.

Interpretation of genetic variants of uncertain significance in atypical hemolytic uremic syndrome.

Mutations in complement proteins predispose to atypical hemolytic uremic syndrome (aHUS). Mutation screening in aHUS is challenging, because most of the disease-associated mutations are individually rare, and a significant proportion of variants consist of missense mutations of unknown significance. The definitive interpretation of a variant of unknown significance (VUS) is often dependent on a reliable functional assay too time-consuming to be used in a diagnostic screening service. Allied research groups have analyzed these VUSs in aHUS.

Functional Characterization of Rare Genetic Variants in the N-Terminus of Complement Factor H in aHUS, C3G, and AMD.

Membranoproliferative glomerulonephritis (MPGN), C3 glomerulopathy (C3G), atypical haemolytic uraemic syndrome (aHUS) and age-related macular degeneration (AMD) have all been strongly linked with dysfunction of the alternative pathway (AP) of complement. A significant proportion of individuals with MPGN, C3G, aHUS and AMD carry rare genetic variants in the CFH gene that cause functional or quantitative deficiencies in the factor H (FH) protein, an important regulator of the AP. In silico analysis of the deleteriousness of rare genetic variants in CFH is not reliable and careful biochemical assessment remains the gold standard. Six N-terminal variants of uncertain significance in CFH were identified in patients with these diseases of the AP and selected for analysis. The variants were produced in Pichia Pastoris in the setting of FH CCPs 1-4, purified by nickel affinity chromatography and size exclusion and characterized by surface plasmon resonance and haemolytic assays as well as by cofactor assays in the fluid phase. A single variant, Q81P demonstrated a profound loss of binding to C3b with consequent loss of cofactor and decay accelerating activity. A further 2 variants, G69E and D130N, demonstrated only subtle defects which could conceivably over time lead to disease progression of more chronic AP diseases such as C3G and AMD. In the variants S159N, A161S, and M162V any functional defect was below the capacity of the experimental assays to reliably detect. This study further underlines the importance of careful biochemical assessment when assigning functional consequences to rare genetic variants that may alter clinical decisions for patients.

Rare variants in CFI, C3 and C9 are associated with high risk of advanced age-related macular degeneration.

To define the role of rare variants in advanced age-related macular degeneration (AMD) risk, we sequenced the exons of 681 genes within all reported AMD loci and related pathways in 2,493 cases and controls. We first tested each gene for increased or decreased burden of rare variants in cases compared to controls. We found that 7.8% of AMD cases compared to 2.3% of controls are carriers of rare missense CFI variants (odds ratio (OR) = 3.6; P = 2 × 10(-8)). There was a predominance of dysfunctional variants in cases compared to controls. We then tested individual variants for association with disease. We observed significant association with rare missense alleles in genes other than CFI. Genotyping in 5,115 independent samples confirmed associations with AMD of an allele in C3 encoding p.Lys155Gln (replication P = 3.5 × 10(-5), OR = 2.8; joint P = 5.2 × 10(-9), OR = 3.8) and an allele in C9 encoding p.Pro167Ser (replication P = 2.4 × 10(-5), OR = 2.2; joint P = 6.5 × 10(-7), OR = 2.2). Finally, we show that the allele of C3 encoding Gln155 results in resistance to proteolytic inactivation by CFH and CFI. These results implicate loss of C3 protein regulation and excessive alternative complement activation in AMD pathogenesis, thus informing both the direction of effect and mechanistic underpinnings of this disorder.

Silencing mediated by the Schizosaccharomyces pombe HIRA complex is dependent upon the Hpc2-like protein, Hip4.

BACKGROUND: HIRA (or Hir) proteins are conserved histone chaperones that function in multi-subunit complexes to mediate replication-independent nucleosome assembly. We have previously demonstrated that the Schizosaccharomyces pombe HIRA proteins, Hip1 and Slm9, form a complex with a TPR repeat protein called Hip3. Here we have identified a new subunit of this complex. METHODOLOGY/PRINCIPAL FINDINGS: To identify proteins that interact with the HIRA complex, rapid affinity purifications of Slm9 were performed. Multiple components of the chaperonin containing TCP-1 complex (CCT) and the 19S subunit of the proteasome reproducibly co-purified with Slm9, suggesting that HIRA interacts with these complexes. Slm9 was also found to interact with a previously uncharacterised protein (SPBC947.08c), that we called Hip4. Hip4 contains a HRD domain which is a characteristic of the budding yeast and human HIRA/Hir-binding proteins, Hpc2 and UBN1. Co-precipitation experiments revealed that Hip4 is stably associated with all of the other components of the HIRA complex and deletion of hip4(+) resulted in the characteristic phenotypes of cells lacking HIRA function, such as temperature sensitivity, an elongated cell morphology and hypersensitivity to the spindle poison, thiabendazole. Moreover, loss of Hip4 function alleviated the heterochromatic silencing of reporter genes located in the mating type locus and centromeres and was associated with increased levels of non-coding transcripts derived from centromeric repeat sequences. Hip4 was also found to be required for the distinct form of silencing that controls the expression of Tf2 LTR retrotransposons. CONCLUSIONS/SIGNIFICANCE: Overall, these results indicate that Hip4 is an integral component of the HIRA complex that is required for transcriptional silencing at multiple loci.

The fission yeast HIRA histone chaperone is required for promoter silencing and the suppression of cryptic antisense transcripts.

The assembly of nucleosomes by histone chaperones is an important component of transcriptional regulation. Here, we have assessed the global roles of the HIRA histone chaperone in Schizosaccharomyces pombe. Microarray analysis indicates that inactivation of the HIRA complex results in increased expression of at least 4% of fission yeast genes. HIRA-regulated genes overlap with those which are normally repressed in vegetatively growing cells, such as targets of the Clr6 histone deacetylase and silenced genes located in subtelomeric regions. HIRA is also required for silencing of all 13 intact copies of the Tf2 long terminal repeat (LTR) retrotransposon. However, the role of HIRA is not restricted to bona fide promoters, because HIRA also suppresses noncoding transcripts from solo LTR elements and spurious antisense transcripts from cryptic promoters associated with transcribed regions. Furthermore, the HIRA complex is essential in the absence of the quality control provided by nuclear exosome-mediated degradation of illegitimate transcripts. This suggests that HIRA restricts genomic accessibility, and consistent with this, the chromosomes of cells lacking HIRA are more susceptible to genotoxic agents that cause double-strand breaks. Thus, the HIRA histone chaperone is required to maintain the protective functions of chromatin.