Evolution: functional evolution of nuclear structure.

The evolution of the nucleus, the defining feature of eukaryotic cells, was long shrouded in speculation and mystery. There is now strong evidence that nuclear pore complexes (NPCs) and nuclear membranes coevolved with the endomembrane system, and that the last eukaryotic common ancestor (LECA) had fully functional NPCs. Recent studies have identified many components of the nuclear envelope in living Opisthokonts, the eukaryotic supergroup that includes fungi and metazoan animals. These components include diverse chromatin-binding membrane proteins, and membrane proteins with adhesive lumenal domains that may have contributed to the evolution of nuclear membrane architecture. Further discoveries about the nucleoskeleton suggest that the evolution of nuclear structure was tightly coupled to genome partitioning during mitosis

Interference with the cytoplasmic tail of gp210 disrupts “close apposition” of nuclear membranes and blocks nuclear pore dilation

We tested the hypothesis that gp210, an integral membrane protein of nuclear pore complexes (NPCs), mediates nuclear pore formation. Gp210 has a large lumenal domain and small COOH-terminal tail exposed to the cytoplasm. We studied the exposed tail. We added recombinant tail polypeptides to Xenopus nuclear assembly extracts, or inhibited endogenous gp210 tails using anti-tail antibodies. Both strategies had no effect on the formation of fused flattened nuclear membranes, but blocked NPC assembly and nuclear growth. Inhibited nuclei accumulated gp210 and some nucleoporin p62, but failed to incorporate nup214/CAN, nup153, or nup98 and were defective for nuclear import of lamin B3. Scanning and transmission EM revealed a lack of “closely apposed” inner and outer membranes, and the accumulation of novel arrested structures including “mini-pores.” We conclude that gp210 has early roles in nuclear pore formation, and that pore dilation is mediated by gp210 and its tail-binding partner(s). We propose that membrane fusion and pore dilation are coupled, acting as a mechanism to control nuclear pore size

SUN-domain proteins: 'Velcro' that links the nucleoskeleton to the cytoskeleton

The novel SUN-domain family of nuclear envelope proteins interacts with various KASH-domain partners to form SUN-domain-dependent 'bridges' across the inner and outer nuclear membranes. These bridges physically connect the nucleus to every major component of the cytoskeleton. SUN-domain proteins have diverse roles in nuclear positioning, centrosome localization, germ-cell development, telomere positioning and apoptosis. By serving both as mechanical adaptors and nuclear envelope receptors, we propose that SUN-domain proteins connect cytoplasmic and nucleoplasmic activities

Barrier-to-autointegration factor: major roles in chromatin decondensation and nuclear assembly

Barrier-to-autointegration factor (BAF) is a DNA-bridging protein, highly conserved in metazoans. BAF binds directly to LEM (LAP2, emerin, MAN1) domain nuclear membrane proteins, including LAP2 and emerin. We used site-directed mutagenesis and biochemical analysis to map functionally important residues in human BAF, including those required for direct binding to DNA or emerin. We also tested wild-type BAF and 25 point mutants for their effects on nuclear assembly in Xenopus egg extracts, which contain ∼12 μM endogenous BAF dimers. Exogenous BAF caused two distinct effects: at low added concentrations, wild-type BAF enhanced chromatin decondensation and nuclear growth; at higher added concentrations, wild-type BAF completely blocked chromatin decondensation and nuclear growth. Mutants fell into four classes, including one that defines a novel functional surface on the BAF dimer. Our results suggest that BAF, unregulated, potently compresses chromatin structure, and that BAF interactions with both DNA and LEM proteins are critical for membrane recruitment and chromatin decondensation during nuclear assembly

Rare BANF1 Alleles and Relatively Frequent EMD Alleles Including `Healthy Lipid' Emerin p.D149H in the ExAC Cohort

Emerin (EMD) and barrier to autointegration factor 1 (BANF1) each bind A-type lamins (LMNA) as fundamental components of nuclear lamina structure. Mutations in LMNA, EMD and BANF1 are genetically linked to many tissue-specific disorders including Emery-Dreifuss muscular dystrophy and cardiomyopathy (LMNA, EMD), lipodystrophy, insulin resistance and type 2 diabetes (LMNA) and progeria (LMNA, BANF1). To explore human genetic variation in these genes, we analyzed EMD and BANF1 alleles in the Exome Aggregation Consortium (ExAC) cohort of 60,706 unrelated individuals. We identified 13 rare heterozygous BANF1 missense variants (p.T2S, p.H7Y, p.D9N, p.S22R, p.G25E, p.D55N, p.D57Y, p.L63P, p.N70T, p.K72R, p.R75W, p.R75Q, p.G79R), and one homozygous variant (p.D9H). Several variants are known (p.G25E) or predicted (e.g., p.D9H, p.D9N, p.L63P) to perturb BANF1 and warrant further study. Analysis of EMD revealed two previously identified variants associated with adult-onset cardiomyopathy (p.K37del, p.E35K) and one deemed `benign' in an Emery-Dreifuss patient (p.D149H). Interestingly p.D149H was the most frequent emerin variant in ExAC, identified in 58 individuals (overall allele frequency 0.06645%), of whom 55 were East Asian (allele frequency 0.8297%). Furthermore, p.D149H associated with four `healthy' traits: reduced triglycerides (-0.336; p = 0.0368), reduced waist circumference (-0.321; p = 0.0486), reduced cholesterol (-0.572; p = 0.000346) and reduced LDL cholesterol (-0.599; p = 0.000272). These traits are distinct from LMNA-associated metabolic disorders and provide the first insight that emerin influences metabolism. We also identified one novel in-frame deletion (p.F39del) and 62 novel emerin missense variants, many of which were relatively frequent and potentially disruptive including p.N91S and p.S143F (0.041% and -0.034% of non-Finnish Europeans, respectively), p.G156S (-0.39% of Africans), p.R204G (-0.18% of Latinx), p.R207P (-0.08% of South Asians) and p.R221L (-0.15% of Latinx). Many novel BANF1 variants are predicted to disrupt dimerization or binding to DNA, histones, emerin or A-type lamins. Many novel emerin variants are predicted to disrupt emerin filament dynamics or binding to BANF1, HDAC3, A-type lamins or other partners. These new human variants provide a foundational resource for future studies to test the molecular mechanisms of BANF1 and emerin function, and to understand the link between emerin variant p.D149H and a `healthy' lipid profile

Barrier to autointegration factor blocks premature cell fusion and maintains adult muscle integrity in C. elegans

Barrier to autointegration factor (BAF) binds double-stranded DNA, selected histones, transcription regulators, lamins, and LAP2–emerin–MAN1 (LEM) domain proteins. During early Caenorhabditis elegans embryogenesis, BAF-1 is required to organize chromatin, capture segregated chromosomes within the nascent nuclear envelope, and assemble lamin and LEM domain proteins in reforming nuclei. In this study, we used C. elegans with a homozygous deletion of the baf-1 gene, which survives embryogenesis and larval stages, to report that BAF-1 regulates maturation and survival of the germline, cell migration, vulva formation, and the timing of seam cell fusion. In the seam cells, BAF-1 represses the expression of the EFF-1 fusogen protein, but fusion still occurs in C. elegans lacking both baf-1 and eff-1. This suggests the existence of an eff-1–independent mechanism for cell fusion. BAF-1 is also required to maintain the integrity of specific body wall muscles in adult animals, directly implicating BAF in the mechanism of human muscular dystrophies (laminopathies) caused by mutations in the BAF-binding proteins emerin and lamin A

The long-term relationship between cannabis and heroin use:An 18-20-year follow-up of the Australian Treatment Outcome Study (ATOS)

Objective: Cannabis use is common among those with opioid use disorders (OUD), but it remains unclear whether cannabis use is associated with an increase or reduction in illicit opioid use. To extend upon previous longitudinal studies with limited follow-ups, the current study examined a within-person reciprocal relationship between cannabis and heroin use at several follow-ups over 18-20-years. Methods: The Australian Treatment Outcome Study (ATOS) recruited 615 people with heroin dependence in 2001-2002 and reinterviewed at 3-, 12-, 24-, 36-months, 11 and 18-20-years post-baseline. Heroin and cannabis use were assessed at each time point using the Opiate Treatment Index (OTI). A random intercept cross-lagged panel model (RI-CLPM) was conducted to identify within-person relationships between cannabis use and heroin use at subsequent follow-ups. Results: After accounting for a range of demographic, other substance use, mental and physical health measures, an increase in cannabis use at 24-months was associated with an increase in heroin use at 36months (Estimate = 0.21, SE = 0.10, p = 0.03). Additionally, an increase in heroin use at 3-months and 24-months post-baseline was associated with a decrease in cannabis use at 12-months (Estimate = -0.27, SE = 0.09, p <0.01) and 36-months post-baseline (Estimate = -0.22, SE = 0.08, p <0.01). All other cross-lagged associations were not significant. Conclusions: Although there was some evidence of a significant relationship between cannabis and heroin use at earlier follow-ups, this was sparse, and inconsistent across time-points. Overall, there was insufficient evidence to suggest a unidirectional or bidirectional relationship between the use of these substances

Neuropsychological, Behavioral, and Anatomical Evolution in Right Temporal Variant Frontotemporal Dementia: A Longitudinal Single Case Analysis

We examine longitudinal clinical and anatomical data for a patient with the right temporal variant of frontotemporal dementia. The patient received comprehensive clinical evaluations and structural MRI scans over three years. She presented with early behavioral deficits and ultimately developed semantic impairments consistent with the semantic variant of primary progressive aphasia. Imaging revealed early atrophy of the right temporal lobe, with later involvement of the left, and pathology confirmed bilateral temporal involvement. Findings support the view that right and left temporal variants reflect early asymmetry of atrophy that may become more bilateral over time, resulting in a mixed clinical picture