The sorting of signaling receptors into and out of cilia relies on the BBSome, a complex of Bardet-Biedl syndrome (BBS) proteins, and on the intraflagellar transport (IFT) machinery. GTP loading onto ...the Arf-like GTPase ARL6/BBS3 drives assembly of a membrane-apposed BBSome coat that promotes cargo entry into cilia, yet how and where ARL6 is activated remains elusive. Here, we show that the Rab-like GTPase IFT27/RABL4, a known component of IFT complex B, promotes the exit of BBSome and associated cargoes from cilia. Unbiased proteomics and biochemical reconstitution assays show that, upon disengagement from the rest of IFT-B, IFT27 directly interacts with the nucleotide-free form of ARL6. Furthermore, IFT27 prevents aggregation of nucleotide-free ARL6 in solution. Thus, we propose that IFT27 separates from IFT-B inside cilia to promote ARL6 activation, BBSome coat assembly, and subsequent ciliary exit, mirroring the process by which BBSome mediates cargo entry into cilia.
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•The IFT-B subunit IFT27/RabL4 directly and selectively binds nucleotide-empty ARL6•IFT27 needs disengagement from IFT-B to recognize ARL6•The exit of BBSome and cargoes from cilia requires IFT27•The BBSome dissociates from IFT trains in the absence of IFT27
The Arf-like GTPase ARL6 triggers BBSome coat assembly and cargo entry into cilia. Now, Liew et al. find that the Rab-like GTPase IFT27 disengages from anterograde IFT complexes to bind and activate nucleotide-empty ARL6 and thereby promote the exit of the BBSome and its associated cargoes from cilia.
Axonal transport of synaptic vesicle precursors (SVPs) is essential for synapse development and function. The conserved ARF-like small GTPase ARL-8 is localized to SVPs and directly activates ...UNC-104/KIF1A, the axonal-transport kinesin for SVPs in C. elegans. It is not clear how ARL-8 is activated in this process. Here we show that part of the BLOC-1-related complex (BORC), previously shown to regulate lysosomal transport, is required to recruit and activate ARL-8 on SVPs. We found mutations in six BORC subunits—blos-1/BLOS1, blos-2/BLOS2, snpn-1/Snapin, sam-4/Myrlysin, blos-7/Lyspersin, and blos-9/MEF2BNB—cause defects in axonal transport of SVPs, leading to ectopic accumulation of synaptic vesicles in the proximal axon. This phenotype is suppressed by constitutively active arl-8 or unc-104 mutants. Furthermore, SAM-4/Myrlysin, a subunit of BORC, promotes the GDP-to-GTP exchange of ARL-8 in vitro and recruits ARL-8 onto SVPs in vivo. Thus, BORC regulates the axonal transport of synaptic materials and synapse formation by controlling the nucleotide state of ARL-8. Interestingly, the other two subunits of BORC essential for lysosomal transport, kxd-1/KXD1 and blos-8/Diaskedin, are not required for the SVP transport, suggesting distinct subunit requirements for lysosomal and SVP trafficking.
•BORC is essential for the axonal transport of synaptic vesicle precursors (SVPs)•Six BORC subunits are essential for SVP transport•Essential BORC subunits are different between lysosome and SVP transport•BORC subunit SAM-4 has guanine nucleotide exchange factor (GEF) activity to ARL-8
BORC is an eight-subunit complex that is known to regulate lysosome transport. In this paper, Niwa et al. show that BORC is essential for the axonal transport of synaptic vesicle precursors and regulates the localization of synaptic vesicles. SAM-4, one of the BORC subunits, has GDP-GTP exchange activity toward small GTPase ARL-8.
Although the clinical signs of prodromal Parkinson's disease (PD) have been identified, little is known about the neural features of the prodromal phase of PD (proPD). The aim of this study was to ...examine the structural network alterations from healthy aging to proPD and to early PD.
181 non-demented and non-depressed participants comprising 55 healthy controls (HCs), 20 proPDs, and 106 de novo PD patients (dPDs) were included in the study and underwent clinical assessment and diffusion tensor imaging scanning. Graph-theoretical analysis and network-based statistics, with age and gender as nuisance covariates, were used.
Compared with HCs and dPDs, proPD patients showed significantly elevated small-worldness and clustering coefficient (Ps < 0.01) and greater local connectivity between regions relating to motor, olfactory and sleep functions (Ps < 0.05). Although dPDs and HCs did not differ on all graph-theoretic metrics, dPD patients showed decreased connectivity within the prefrontal regions and between the left temporal and occipital lobes (P < 0.05). The connectivity strength between these regions significantly distinguished between diagnostic groups. Connectivity between bilateral SMAs was correlated with UPSIT in HCs and with UPDRS-III in dPDs. Connectivity between the right SMA and putamen was correlated RBDSQ in proPDs.
Increased network efficiency and connectivity of proPDs and decreased local connectivity of dPDs might suggest the emergence and dissipation of neural compensation in the prodromal phase and in early PD, respectively. Nonetheless, longitudinal studies are needed to follow up the long-term structural network changes of proPD patients.
•Prodromal Parkinson patients (proPDs) show increased small-worldness.•ProPDs exhibit greater subnetwork connectivity than controls and Parkinson patients.•Increased structural connectome in proPD suggests neural compensation or plasticity.
The steroid hormone ecdysone induces DNA amplification and subsequent DNA puff formation in late fourth larval instar salivary gland polytene chromosomes of the fungus fly,
Sciara coprophila
. ...Previous in vitro studies on DNA puff II/9A in
Sciara
demonstrated that the ecdysone receptor (ScEcR-A) efficiently binds an ecdysone response element adjacent to the origin recognition complex binding site within the II/9A amplification origin, implying a role for ScEcR-A in amplification. Here, we extrapolate the molecular details from locus II/9A to the rest of the genome using immunofluorescence with a ScEcR-A-specific antibody. ScEcR-A binds all DNA puff sites just as amplification begins and persists throughout the processes of amplification, transcription, and puffing. Ecdysone injections into pre-amplification stage larvae prematurely induce both DNA amplification and ScEcR-A binding to DNA puff sites. These data are consistent with a direct role for ScEcR-A in DNA amplification.
Regulation of DNA replication is critical, and loss of control can lead to DNA amplification. Naturally occurring, developmentally regulated DNA amplification occurs in the DNA puffs of the late ...larval salivary gland giant polytene chromosomes in the fungus fly, Sciara coprophila. The steroid hormone ecdysone induces DNA amplification in Sciara, and the amplification origin of DNA puff II/9A contains a putative binding site for the ecdysone receptor (EcR). We report here the isolation, cloning, and characterizing of two ecdysone receptor isoforms in Sciara (ScEcR-A and ScEcR-B) and the heterodimeric partner, ultraspiracle (ScUSP). ScEcR-A is the predominant isoform in larval tissues and ScEcR-B in adult tissues, contrary to the pattern in Drosophila. Moreover, ScEcR-A is produced at amplification but is absent just prior. We discuss these results in relation to the model of ecdysone regulation of DNA amplification.
Most classification systems for age-related macular degeneration (AMD) were developed from patients in clinical trials. We aimed to validate the Age-Related Eye Diseases Study (AREDS) simplified ...severity scale of AMD classification using 5- and 10-year incident late AMD data from the population-based Blue Mountains Eye Study (BMES) cohort.
Comparative study of population-based cohort and clinical trial.
Blue Mountains Eye Study participants 40 to 97 years of age at baseline (n = 2134) and AREDS participants 55 to 80 years of age (n = 3640).
In the BMES, AMD lesions were graded from stereoscopic color photographs and were classified according to the AREDS simplified severity scale. The AREDS simplified scale calculates a risk score based on the number of early AMD risk factors (large drusen and pigment abnormalities) in both eyes that can range from 0 to 4.
Five- and 10-year incident late AMD (presence of geographic atrophy or choroidal neovascularization).
The AREDS simplified scale performed similarly when applied to both the BMES population-based participants and the AREDS clinical trial-based participants in predicting 5- and 10-year incidence of late AMD. For scores 0 to 4, the 5-year incidence rates for the BMES compared with the AREDS were 0.2% versus 0.4%, 3.1% versus 3.1%, 12.1% versus 11.8%, 13.5% versus 25.9%, and 47.1% versus 47.3%, respectively. The corresponding 10-year incidence rates for the BMES compared with the AREDS were 0.7% versus 1.5%, 7.3% versus 8.4%, 36.6% versus 27.6%, 20.0% versus 52.7%, and 75.0% versus 71.4%, respectively.
The AREDS simplified severity scale classified late AMD risk levels similarly when applied to population-based and clinical trial samples. These results support the robustness of the AREDS simplified severity scale.
Fractals represent a type of derived geometric pattern that permits the characterization of the branching pattern of retinal vessels. We examined a new semiautomated method to measure retinal vessel ...fractals.
Methodology study.
Three hundred randomly selected participants from the population-based Blue Mountains Eye Study.
We developed a semiautomated computer program to measure the fractal dimension (D(f)) of the retinal vessels from digitized images of disk-centered retinal photographs. Two trained graders masked to participant characteristics measured D(f) of right eye images of participants. Reliability was determined by repeat grading of the images from 60 participants, and association with systolic and diastolic blood pressure was examined in all 300 participants.
D(f) of the retinal vessels.
Mean D(f) was 1.437 with a standard deviation of 0.025. Intragrader and intergrader reliability estimates were high with intraclass correlation ranging from 0.93 to 0.95. D(f) was inversely correlated with age (r = -0.42, P = 0.001) and systolic blood pressure (r = -0.29, P<0.0001). After adjustment for age and sex, mean D(f) was significantly lower in participants with than without hypertension (D(f) difference 0.01, P = 0.02).
The D(f) of the retinal vessels can be reliably measured from photographs and shows a strong inverse correlation with blood pressure. These data suggest that the D(f) may be a measure of early microvascular alterations from elevated blood pressure. Further studies to examine the systemic and ocular correlates of the D(f) of the retinal vessels are needed.
To describe the prevalence, risk factors, and associations of vitreoretinal interface (VRI) abnormalities in a population-based study of older adults.
Cross-sectional analysis of cohort study ...participants.
Of the 1149 participants (mean age, 76.1 ± 6.9 years) in the 15-year Blue Mountains Eye Study follow-up examination from 2007 through 2009, 905 (1791 eyes) had gradable time-domain or spectral-domain OCT scans of the macula from at least 1 eye.
OCT scans were graded according to the International Vitreomacular Traction Study Group classification system of VRI abnormalities. Best-corrected visual acuity (BCVA) was recorded.
Prevalence of VRIs.
Overall, 451 participants showed any VRI abnormality (49.8%). Prevalence of VRI abnormality by person was: vitreomacular adhesion (VMA), 33.6%; vitreomacular traction (VMT), 1.6%; epiretinal membrane (ERM), 21.4%; full-thickness macular hole (FTMH), 0.7%; and lamellar macular hole (LMH), 0.7%. Twenty-two percent of VMAs were focal, and 78% were broad based; 76% of VMTs were focal, and 24% were broad based. All FTMHs observed were large (>400 μm), with mean aperture size of 573 μm (range, 459–771 μm). Increased age was associated with higher ERM and lower VMA prevalence (P < 0.001 for both). Pseudophakia and myopia were associated with ERM (age- and sex-adjusted odds ratios ORs, 1.48 95% confidence interval (CI), 1.01–2.17 and 1.72 95% CI, 1.05–2.81, respectively). Moderate or severe ERM and FTMH were associated with worse BCVA of 9.2 Early Treatment Diabetic Retinopathy Study (ETDRS) letters (95% CI, 3.4–15.0 ETDRS letters; P = 0.008) and 26.0 ETDRS letters (95% CI, 10.9–41.1 ETDRS letters; P = 0.001), respectively.
The prevalence of VRI abnormalities is high in older individuals. Epiretinal membrane was associated with increasing age, pseudophakia, and myopia. Epiretinal membrane and FTMH may account for significant visual loss in the affected eye. This study provided useful population-based data on the prevalence of VRI abnormalities in older individuals.
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