Recessive mutations in SPTBN2 implicate β-III spectrin in both cognitive and motor development

β-III spectrin is present in the brain and is known to be important in the function of the cerebellum. Heterozygous mutations in SPTBN2, the gene encoding β-III spectrin, cause Spinocerebellar Ataxia Type 5 (SCA5), an adult-onset, slowly progressive, autosomal-dominant pure cerebellar ataxia. SCA5 is sometimes known as "Lincoln ataxia," because the largest known family is descended from relatives of the United States President Abraham Lincoln. Using targeted capture and next-generation sequencing, we identified a homozygous stop codon in SPTBN2 in a consanguineous family in which childhood developmental ataxia co-segregates with cognitive impairment. The cognitive impairment could result from mutations in a second gene, but further analysis using whole-genome sequencing combined with SNP array analysis did not reveal any evidence of other mutations. We also examined a mouse knockout of β-III spectrin in which ataxia and progressive degeneration of cerebellar Purkinje cells has been previously reported and found morphological abnormalities in neurons from prefrontal cortex and deficits in object recognition tasks, consistent with the human cognitive phenotype. These data provide the first evidence that β-III spectrin plays an important role in cortical brain development and cognition, in addition to its function in the cerebellum; and we conclude that cognitive impairment is an integral part of this novel recessive ataxic syndrome, Spectrin-associated Autosomal Recessive Cerebellar Ataxia type 1 (SPARCA1). In addition, the identification of SPARCA1 and normal heterozygous carriers of the stop codon in SPTBN2 provides insights into the mechanism of molecular dominance in SCA5 and demonstrates that the cell-specific repertoire of spectrin subunits underlies a novel group of disorders, the neuronal spectrinopathies, which includes SCA5, SPARCA1, and a form of West syndrome

Intermediate instability at high temperature leads to low pathway efficiency for an in vitro reconstituted system of gluconeogenesis in Sulfolobus solfataricus.

Four enzymes of the gluconeogenic pathway in Sulfolobus solfataricus were purified and kinetically characterized. The enzymes were reconstituted in vitro to quantify the contribution of temperature instability of the pathway intermediates to carbon loss from the system. The reconstituted system, consisting of phosphoglycerate kinase, glyceraldehyde 3-phosphate dehydrogenase, triose phosphate isomerase and the fructose 1,6-bisphosphate aldolase/phosphatase, maintained a constant consumption rate of 3-phosphoglycerate and production of fructose 6-phosphate over a 1-h period. Cofactors ATP and NADPH were regenerated via pyruvate kinase and glucose dehydrogenase. A mathematical model was constructed on the basis of the kinetics of the purified enzymes and the measured half-life times of the pathway intermediates. The model quantitatively predicted the system fluxes and metabolite concentrations. Relative enzyme concentrations were chosen such that half the carbon in the system was lost due to degradation of the thermolabile intermediates dihydroxyacetone phosphate, glyceraldehyde 3-phosphate and 1,3-bisphosphoglycerate, indicating that intermediate instability at high temperature can significantly affect pathway efficiency

The polymorphic variant rs1800734 influences methylation acquisition and allele-specific TFAP4 binding in the MLH1 promoter leading to differential mRNA expression

The raw data is available on Mendeley at https://data.mendeley.com/datasets/hfpbctm7tg/draft?a=1c91e494-cadc-4be0-a8ff-91d8736a28e7© The Author(s) 2019. Expression of the mismatch repair gene MutL homolog 1 (MLH1) is silenced in a clinically important subgroup of sporadic colorectal cancers. These cancers exhibit hypermutability with microsatellite instability (MSI) and differ from microsatellite-stable (MSS) colorectal cancers in both prognosis and response to therapies. Loss of MLH1 is usually due to epigenetic silencing with associated promoter methylation; coding somatic mutations rarely occur. Here we use the presence of a colorectal cancer (CRC) risk variant (rs1800734) within the MLH1 promoter to investigate the poorly understood mechanisms of MLH1 promoter methylation and loss of expression. We confirm the association of rs1800734 with MSI+ but not MSS cancer risk in our own data and by meta-analysis. Using sensitive allele-specific detection methods, we demonstrate that MLH1 is the target gene for rs1800734 mediated cancer risk. In normal colon tissue, small allele-specific differences exist only in MLH1 promoter methylation, but not gene expression. In contrast, allele-specific differences in both MLH1 methylation and expression are present in MSI+ cancers. We show that MLH1 transcriptional repression is dependent on DNA methylation and can be reversed by a methylation inhibitor. The rs1800734 allele influences the rate of methylation loss and amount of re-expression. The transcription factor TFAP4 binds to the rs1800734 region but with much weaker binding to the risk than the protective allele. TFAP4 binding is absent on both alleles when promoter methylation is present. Thus we propose that TFAP4 binding shields the protective rs1800734 allele of the MLH1 promoter from BRAF induced DNA methylation more effectively than the risk allele.Funding was provided by a Medical Research Council New Investigator Research Grant (MR/P000738/1). Core funding to the Wellcome Trust Centre for Human Genetics was provided by the Wellcome Trust (090532/Z/09/Z). D.T., N.S. and D.F. were supported by the EPIGENOMICS FLAGSHIP PROJECT- EPIGEN (project number 08934412) and by University of Insubria. M.T. and S.K. were funded by Ludwig Cancer Research