Mxc, a Drosophila homolog of mental retardation-associated gene NPAT, maintains neural stem cell fate

Extended range proteomic analysis of blood plasma from schizophrenia patients

Introduction

The high prevalence of schizophrenia worldwide makes it necessary to proceed from subjective assessment of patient's clinical symptoms in diagnosis making to searching for circulating blood biomarkers. On the one hand, searching for molecular markers and targets for therapeutics will make it possible to refine and detail the molecular mechanisms of pathology development, while on the other hand, it will offer new opportunities for elaborating novel approaches to disease diagnosis and enhance efficacy and timeliness of drug therapy.

Methods

In this study, we performed an extended-range proteomic analysis of plasma samples collected from 48 study subjects with confirmed diagnosis of schizophrenia and 50 healthy volunteers. The high-resolution tandem mass spectra recorded in the data-dependent acquisition mode were analyzed using the MaxQuant algorithm for the library of known protein sequences and the PowerNovo algorithm for de novo protein sequencing.

Results

It was demonstrated that both strategies show similar results for high-abundance proteins (≥1 μg/mL). For mid-abundance (10 ng/mL - 1 μg/mL) and low-abundance (<10 ng/mL) proteins, the results obtained by the two search strategies complement each other.

Discussion

Group-specific proteins for the samples of schizophrenia patients were identified, presumably being involved in synaptic plasticity, angiogenesis, transcriptional regulation, protein stabilization and degradation.

The FAcilitates Chromatin Transcription complex regulates the ratio of glycolysis to oxidative phosphorylation in neural stem cells

Defects in the FAcilitates Chromatin Transcription (FACT) complex, a histone chaperone composed of SSRP1 and SUPT16H, are implicated in intellectual disability. Here, we reveal that the FACT complex promotes glycolysis and sustains the correct cell fate of neural stem cells/neuroblasts in the Drosophila 3rd instar larval central brain. We show that the FACT complex binds to the promoter region of the estrogen-related receptor (ERR) gene and positively regulates ERR expression. ERR is known to act as an aerobic glycolytic switch by upregulating the enzymes required for glycolysis. Dysfunction of the FACT complex leads to the downregulation of ERR transcription, resulting in a decreased ratio of glycolysis to oxidative phosphorylation (G/O) in neuroblasts. Consequently, neuroblasts exhibit smaller cell sizes, lower proliferation potential, and altered cell fates. Overexpression of ERR or suppression of mitochondrial oxidative phosphorylation in neuroblasts increases the relative G/O ratio and rescues defective phenotypes caused by dysfunction of the FACT complex. Thus, the G/O ratio, mediated by the FACT complex, plays a crucial role in neuroblast cell fate maintenance. Our study may shed light on the mechanism by which mutations in the FACT complex lead to intellectual disability in humans.

Germline NPAT inactivating variants as cause of hereditary colorectal cancer

Two independent exome sequencing initiatives aimed to identify new genes involved in the predisposition to nonpolyposis colorectal cancer led to the identification of heterozygous loss-of-function variants in NPAT, a gene that encodes a cyclin E/CDK2 effector required for S phase entry and a coactivator of histone transcription, in two families with multiple members affected with colorectal cancer. Enrichment of loss-of-function and predicted deleterious NPAT variants was identified in familial/early-onset colorectal cancer patients compared to non-cancer gnomAD individuals, further supporting the association with the disease. Previous studies in Drosophila models showed that NPAT abrogation results in chromosomal instability, increase of double strand breaks, and induction of tumour formation. In line with these results, colorectal cancers with NPAT somatic variants and no DNA repair defects have significantly higher aneuploidy levels than NPAT-wildtype colorectal cancers. In conclusion, our findings suggest that constitutional inactivating NPAT variants predispose to mismatch repair-proficient nonpolyposis colorectal cancer.

Histone locus bodies: a paradigm for how nuclear biomolecular condensates control cell cycle regulated gene expression

Histone locus bodies (HLBs) are biomolecular condensates that assemble at replication-dependent (RD) histone genes in animal cells. These genes produce unique mRNAs that are not polyadenylated and instead end in a conserved 3' stem loop critical for coordinated production of histone proteins during S phase of the cell cycle. Several evolutionarily conserved factors necessary for synthesis of RD histone mRNAs concentrate only in the HLB. Moreover, because HLBs are present throughout the cell cycle even though RD histone genes are only expressed during S phase, changes in HLB composition during cell cycle progression drive much of the cell cycle regulation of RD histone gene expression. Thus, HLBs provide a powerful opportunity to determine the cause-and-effect relationships between nuclear body formation and cell cycle regulated gene expression. In this review, we focus on progress during the last five years that has advanced our understanding of HLB biology.

HR repair pathway plays a crucial role in maintaining neural stem cell fate under irradiation stress

Environmental stress can cause mutation or genomic instability in stem cells which, in some cases, leads to tumorigenesis. Mechanisms to monitor and eliminate these mutant stem cells remain elusive. Here, using the Drosophila larval brain as a model, we show that X-ray irradiation (IR) at the early larval stage leads to accumulation of nuclear Prospero (Pros), resulting in premature differentiation of neural stem cells (neuroblasts, NBs). Through NB-specific RNAi screenings, we determined that it is the Mre11-Rad50-Nbs1 complex and the homologous recombination (HR) repair pathway, rather than non-homologous end-joining pathway that plays, a dominant role in the maintenance of NBs under IR stress. The DNA damage sensor ATR/mei-41 is shown to act to prevent IR-induced nuclear Pros in a WRNexo-dependent manner. The accumulation of nuclear Pros in NBs under IR stress, leads to NB cell fate termination, rather than resulting in mutant cell proliferation. Our study reveals an emerging mechanism for the HR repair pathway in maintaining neural stem cell fate under irradiation stress.

Pipsqueak family genes dan/danr antagonize nuclear Pros to prevent neural stem cell aging in Drosophila larval brains

Neural stem cell aging is a fundamental question in neurogenesis. Premature nuclear Pros is considered as an indicator of early neural stem cell aging in Drosophila. The underlying mechanism of how neural stem cells prevent premature nuclear Pros remains largely unknown. Here we identified that two pipsqueak family genes, distal antenna (dan) and distal antenna-related (danr), promote the proliferation of neural stem cells (also called neuroblasts, NBs) in third instar larval brains. In the absence of Dan and Danr (dan/danr), the NBs produce fewer daughter cells with smaller lineage sizes. The larval brain NBs in dan/danr clones show premature accumulation of nuclear Prospero (Pros), which usually appears in the terminating NBs at early pupal stage. The premature nuclear Pros leads to NBs cell cycle defects and NB identities loss. Removal of Pros from dan/danr MARCM clones prevents lineage size shrinkage and rescues the loss of NB markers. We propose that the timing of nuclear Pros is after the downregulation of dan/danr in the wt terminating NBs. dan/danr and nuclear Pros are mutually exclusive in NBs. In addition, dan/danr are also required for the late temporal regulator, Grainyhead (Grh), in third instar larval brains. Our study uncovers the novel function of dan/danr in NBs cell fate maintenance. dan/danr antagonize nuclear Pros to prevent NBs aging in Drosophila larval brains.

Co-dependent regulation of p-BRAF and potassium channel KCNMA1 levels drives glioma progression

BRAF mutations have been found in gliomas which exhibit abnormal electrophysiological activities, implying their potential links with the ion channel functions. In this study, we identified the Drosophila potassium channel, Slowpoke (Slo), the ortholog of human KCNMA1, as a critical factor involved in dRaf^GOF glioma progression. Slo was upregulated in dRaf^GOF glioma. Knockdown of slo led to decreases in dRaf^GOF levels, glioma cell proliferation, and tumor-related phenotypes. Overexpression of slo in glial cells elevated dRaf expression and promoted cell proliferation. Similar mutual regulations of p-BRAF and KCNMA1 levels were then recapitulated in human glioma cells with the BRAF mutation. Elevated p-BRAF and KCNMA1 were also observed in HEK293T cells upon the treatment of 20 mM KCl, which causes membrane depolarization. Knockdown KCNMA1 in these cells led to a further decrease in cell viability. Based on these results, we conclude that the levels of p-BRAF and KCNMA1 are co-dependent and mutually regulated. We propose that, in depolarized glioma cells with BRAF mutations, high KCNMA1 levels act to repolarize membrane potential and facilitate cell growth. Our study provides a new strategy to antagonize the progression of gliomas as induced by BRAF mutations.