Inositol Hexakisphosphate Primes Syndapin I/PACSIN 1 Activation In Endocytosis

Endocytosis is controlled by a well-orchestrated molecular machinery, where the individual players as well as their precise interactions are not fully understood. We now show that syndapin I/PACSIN 1 is expressed in pancreatic β cells and that its knockdown abrogates β cell endocytosis leading to disturbed plasma membrane protein homeostasis, as exemplified by an elevated density of L-type Ca2+ channels. Intriguingly, inositol hexakisphosphate (InsP6) activates casein kinase 2 (CK2) phosphorylating syndapin I/PACSIN 1, promoting interactions between syndapin I/PACSIN 1 and neural Wiskott-Aldrich syndrome protein (N-WASP) thereby driving β cell endocytosis. Dominant-negative interference with endogenous syndapin I/PACSIN 1 protein complexes, by overexpression of the syndapin I/PACSIN 1 SH3 domain, decreases InsP6-stimulated endocytosis. InsP6 thus promotes syndapin I/PACSIN 1 priming by CK2-dependent phosphorylation, which endows the syndapin I/PACSIN 1 SH3 domain with the capability to interact with the endocytic machinery and thereby initiate endocytosis, as exemplified in β cells.

CHARGE syndrome protein CHD7 regulates epigenomic activation of enhancers in granule cell precursors and gyrification of the cerebellum

Regulation of chromatin plays fundamental roles in the development of the brain. Haploinsufficiency of the chromatin remodeling enzyme CHD7 causes CHARGE syndrome, a genetic disorder that affects the development of the cerebellum. However, how CHD7 controls chromatin states in the cerebellum remains incompletely understood. Using conditional knockout of CHD7 in granule cell precursors in the mouse cerebellum, we find that CHD7 robustly promotes chromatin accessibility, active histone modifications, and RNA polymerase recruitment at enhancers. In vivo profiling of genome architecture reveals that CHD7 concordantly regulates epigenomic modifications associated with enhancer activation and gene expression of topologically-interacting genes. Genome and gene ontology studies show that CHD7-regulated enhancers are associated with genes that control brain tissue morphogenesis. Accordingly, conditional knockout of CHD7 triggers a striking phenotype of cerebellar polymicrogyria, which we have also found in a case of CHARGE syndrome. Finally, we uncover a CHD7-dependent switch in the preferred orientation of granule cell precursor division in the developing cerebellum, providing a potential cellular basis for the cerebellar polymicrogyria phenotype upon loss of CHD7. Collectively, our findings define epigenomic regulation by CHD7 in granule cell precursors and identify abnormal cerebellar patterning upon CHD7 depletion, with potential implications for our understanding of CHARGE syndrome.

Targeting the actin nucleation promoting factor WASp provides a therapeutic approach for hematopoietic malignancies

Cancer cells depend on actin cytoskeleton rearrangement to carry out hallmark malignant functions including activation, proliferation, migration and invasiveness. Wiskott–Aldrich Syndrome protein (WASp) is an actin nucleation-promoting factor and is a key regulator of actin polymerization in hematopoietic cells. The involvement of WASp in malignancies is incompletely understood. Since WASp is exclusively expressed in hematopoietic cells, we performed in silico screening to identify small molecule compounds (SMCs) that bind WASp and promote its degradation. We describe here one such identified molecule; this WASp-targeting SMC inhibits key WASp-dependent actin processes in several types of hematopoietic malignancies in vitro and in vivo without affecting naïve healthy cells. This small molecule demonstrates limited toxicity and immunogenic effects, and thus, might serve as an effective strategy to treat specific hematopoietic malignancies in a safe and precisely targeted manner.

The Troyer syndrome protein spartin mediates selective autophagy of lipid droplets

Lipid droplets (LDs) are crucial organelles for energy storage and lipid homeostasis. Autophagy of LDs is an important pathway for their catabolism, but the molecular mechanisms mediating targeting of LDs for degradation by selective autophagy (lipophagy) are unknown. Here we identify spartin as a receptor localizing to LDs and interacting with core autophagy machinery, and we show that spartin is required to deliver LDs to lysosomes for triglyceride (TG) mobilization. Mutations in SPART (encoding spartin) lead to Troyer syndrome, a form of hereditary spastic paraplegia. We find that interfering with spartin function leads to LD and TG accumulation in motor cortex neurons of mice. Our findings thus identify spartin as a lipophagy receptor and suggest that impaired LD turnover may contribute to Troyer syndrome development.

Mutational screening of WASP gene in patients with Wiskott-Aldrich syndrome

The Wiskott-Aldrich syndrome (WAS) is a rare X-linked recessive immunodeficiency disorder characterized by thrombocytopenia and small-sized platelets, eczema, recurrent bacterial and viral infections, higher incidence of autoimmunity and an increased risk of malignancies. WAS occurs due to the mutation or loss of Wiskott-Aldrich Syndrome Protein (WASP) gene located on Xp11.22 – p11.23 of the short arm of the X chromosome. The absence of functional WASP leads to severe clinical symptoms that results in the deaths of patients if they are not diagnosed and treated early. The objective of the study was to identify mutations in the WASP gene of families with children diagnosed with WAS.The whole coding sequence and the intron-exon flanking regions of the WASP were sequenced by Sanger method. Two cases of children who has WAS were found tocarrymutations in the WASP gene. A c.702insAC mutation leadeda frameshift at position of codon 236 and terminated the protein at the position of codon 262 was identified in patient WA007 and a c.91G>A mutation that transformed glutamic acid to lysineat codon 31 was determined in patient WA010.This study provides a data set and screening of mutations in theWASP gene inVietnamese patientsto further identify the genetic causes and contribute to the clinical management and genetic counseling for the affected families.

Expansion of the Genotypic and Phenotypic Spectrum of WASF1-Related Neurodevelopmental Disorder

In humans, de novo truncating variants in WASF1 (Wiskott–Aldrich syndrome protein family member 1) have been linked to presentations of moderate-to-profound intellectual disability (ID), autistic features, and epilepsy. Apart from one case series, there is limited information on the phenotypic spectrum and genetic landscape of WASF1-related neurodevelopmental disorder (NDD). In this report, we describe detailed clinical characteristics of six individuals with WASF1-related NDD. We demonstrate a broader spectrum of neurodevelopmental impairment including more mildly affected individuals. Further, we report new variant types, including a copy number variant (CNV), resulting in the partial deletion of WASF1 in monozygotic twins, and three missense variants, two of which alter the same residue, p.W161. This report adds further evidence that de novo variants in WASF1 cause an autosomal dominant NDD.

MeCP2 is a microsatellite binding protein that protects CA repeats from nucleosome invasion

The Rett syndrome protein MeCP2 was described as a methyl-CpG-binding protein, but its exact function remains unknown. Here we show that mouse MeCP2 is a microsatellite binding protein that specifically recognizes hydroxymethylated CA repeats. Depletion of MeCP2 alters chromatin organization of CA repeats and lamina-associated domains and results in nucleosome accumulation on CA repeats and genome-wide transcriptional dysregulation. The structure of MeCP2 in complex with a hydroxymethylated CA repeat reveals a characteristic DNA shape, with considerably modified geometry at the 5-hydroxymethylcytosine, which is recognized specifically by Arg133, a key residue whose mutation causes Rett syndrome. Our work identifies MeCP2 as a microsatellite DNA binding protein that targets the 5hmC-modified CA-rich strand and maintains genome regions nucleosome-free, suggesting a role for MeCP2 dysfunction in Rett syndrome.