Ubiquitylation of BBSome is required for ciliary assembly and signaling

Clinical features of a novel compound heterozygous genotype of the BBS2 gene: a case report

Bardet-Biedl syndrome is a rare autosomal recessive genetic disorder with heterogenous clinical manifestations. The present study reports the clinical features of a novel compound heterozygous genotype of the BBS2 gene in a 14-year-old girl and her 6-year-old sister who had complaints of early-onset low vision. Fundus images revealed retinitis pigmentosa-like changes, and full-field electroretinograms showed no amplitude for the rod or cone response in both patients. Interestingly, nystagmus was observed in the older sister. On physical examination, the sisters had moderate obesity without polydactyly, hypogonadism, or intellectual disability. Exome sequencing revealed a novel compound heterozygous genotype of BBS2 in the sisters, namely the paternally inherited NM_031885.5:c.534 + 1G > T variant and the maternally inherited NM_031885.5:c.700C > T (p.Arg234Ter) variant. Both variants were classified as pathogenic according to the American College of Medical Genetics and Genomics guidelines. This study provides useful information on the genotype-phenotype relationships of the BBS2 gene for genetic counseling and diagnosis.

Genetic context modulates aging and degeneration in the murine retina

Background

Age is the principal risk factor for neurodegeneration in both the retina and brain. The retina and brain share many biological properties; thus, insights into retinal aging and degeneration may shed light onto similar processes in the brain. Genetic makeup strongly influences susceptibility to age-related retinal disease. However, studies investigating retinal aging have not sufficiently accounted for genetic diversity. Therefore, examining molecular aging in the retina across different genetic backgrounds will enhance our understanding of human-relevant aging and degeneration in both the retina and brain-potentially improving therapeutic approaches to these debilitating conditions.

Methods

Transcriptomics and proteomics were employed to elucidate retinal aging signatures in nine genetically diverse mouse strains (C57BL/6J, 129S1/SvlmJ, NZO/HlLtJ, WSB/EiJ, CAST/EiJ, PWK/PhK, NOD/ShiLtJ, A/J, and BALB/cJ) across lifespan. These data predicted human disease-relevant changes in WSB and NZO strains. Accordingly, B6, WSB and NZO mice were subjected to human-relevant in vivo examinations at 4, 8, 12, and/or 18M, including: slit lamp, fundus imaging, optical coherence tomography, fluorescein angiography, and pattern/full-field electroretinography. Retinal morphology, vascular structure, and cell counts were assessed ex vivo.

Results

We identified common molecular aging signatures across the nine mouse strains, which included genes associated with photoreceptor function and immune activation. Genetic background strongly modulated these aging signatures. Analysis of cell type-specific marker genes predicted age-related loss of photoreceptors and retinal ganglion cells (RGCs) in WSB and NZO, respectively. Fundus exams revealed retinitis pigmentosa-relevant pigmentary abnormalities in WSB retinas and diabetic retinopathy (DR)-relevant cotton wool spots and exudates in NZO retinas. Profound photoreceptor dysfunction and loss were confirmed in WSB. Molecular analyses indicated changes in photoreceptor-specific proteins prior to loss, suggesting photoreceptor-intrinsic dysfunction in WSB. In addition, age-associated RGC dysfunction, loss, and concomitant microvascular dysfunction was observed in NZO mice. Proteomic analyses revealed an early reduction in protective antioxidant processes, which may underlie increased susceptibility to DR-relevant pathology in NZO.

Conclusions

Genetic context is a strong determinant of retinal aging, and our multi-omics resource can aid in understanding age-related diseases of the eye and brain. Our investigations identified and validated WSB and NZO mice as improved preclinical models relevant to common retinal neurodegenerative diseases.

Functional Divergence and Origin of the Vertebrate Praja Family

The Praja family is an E3 ubiquitin ligase, promoting polyubiquitination and subsequent degradation of substrates. It comprises two paralogs, praja1 and praja2. Prior research suggests these paralogs have undergone functional divergence, with examples, such as their distinct roles in neurite outgrowth. However, the specific evolutionary trajectories of each paralog remain largely unexplored preventing mechanistic understanding of functional differences between paralogs. Here, we investigated the phylogeny and divergence of the vertebrate Praja family through molecular evolutionary analysis. Phylogenetic examination of the vertebrate praja revealed that praja1 and praja2 originated from the common ancestor of placentals via gene duplication, with praja1 evolving at twice the rate of praja2 shortly after the duplication. Moreover, a unique evolutionary trajectory for praja1 relative to other vertebrate Praja was indicated, as evidenced by principal component analysis on GC content, codon usage frequency, and amino acid composition. Subsequent motif/domain comparison revealed conserved N terminus and C terminus in praja1 and praja2, together with praja1-specific motifs, including nuclear localization signal and Ala-Gly-Ser repeats. The nuclear localization signal was demonstrated to be functional in human neuroblastoma SH-SY5Y cells using deletion mutant, while praja2 was exclusively expressed in the nucleus. These discoveries contribute to a more comprehensive understanding of the Praja family's phylogeny and suggest a functional divergence between praja1 and praja2. Specifically, the shift of praja1 into the nucleus implies the degradation of novel substrates located in the nucleus as an evolutionary consequence.

Recent advances in the understanding of cilia mechanisms and their applications as therapeutic targets

The primary cilium is a single immotile microtubule-based organelle that protrudes into the extracellular space. Malformations and dysfunctions of the cilia have been associated with various forms of syndromic and non-syndromic diseases, termed ciliopathies. The primary cilium is therefore gaining attention due to its potential as a therapeutic target. In this review, we examine ciliary receptors, ciliogenesis, and ciliary trafficking as possible therapeutic targets. We first discuss the mechanisms of selective distribution, signal transduction, and physiological roles of ciliary receptors. Next, pathways that regulate ciliogenesis, specifically the Aurora A kinase, mammalian target of rapamycin, and ubiquitin-proteasome pathways are examined as therapeutic targets to regulate ciliogenesis. Then, in the photoreceptors, the mechanism of ciliary trafficking which takes place at the transition zone involving the ciliary membrane proteins is reviewed. Finally, some of the current therapeutic advancements highlighting the role of large animal models of photoreceptor ciliopathy are discussed.

Proteomics and phosphoproteomics profiling in glutamatergic neurons and microglia in an iPSC model of Jansen de Vries Syndrome

Background

Jansen de Vries Syndrome (JdVS) is a rare neurodevelopmental disorder (NDD) caused by gain-of-function (GOF) truncating mutations in PPM1D exons 5 or 6. PPM1D is a serine/threonine phosphatase that plays an important role in the DNA damage response (DDR) by negatively regulating TP53 (P53). JdVS-associated mutations lead to the formation of a truncated PPM1D protein that retains catalytic activity and has a GOF effect because of reduced degradation. Somatic PPM1D exons 5 and 6 truncating mutations are well-established factors in a number of cancers, due to excessive dephosphorylation and reduced function of P53 and other substrates involved in DDR. Children with JdVS have a variety of neurodevelopmental, psychiatric, and physical problems. In addition, a small fraction has acute neuropsychiatric decompensation apparently triggered by infection or severe non-infectious environmental stress factors.

Methods

To understand the molecular basis of JdVS, we developed an induced pluripotent stem cell (iPSC) model system. iPSCs heterozygous for the truncating variant (PPM1D+/tr), were made from a patient, and control lines engineered using CRISPR-Cas9 gene editing. Proteomics and phosphoprotemics analyses were carried out on iPSC-derived glutamatergic neurons and microglia from three control and three PPM1D+/tr iPSC lines. We also analyzed the effect of the TLR4 agonist, lipopolysaccharide, to understand how activation of the innate immune system in microglia could account for acute behavioral decompensation.

Results

One of the major findings was the downregulation of POGZ in unstimulated microglia. Since loss-of-function variants in the POGZ gene are well-known causes of autism spectrum disorder, the decrease in PPM1D+/tr microglia suggests this plays a role in the neurodevelopmental aspects of JdVS. In addition, neurons, baseline, and LPS-stimulated microglia show marked alterations in the expression of several E3 ubiquitin ligases, most notably UBR4, and regulators of innate immunity, chromatin structure, ErbB signaling, and splicing. In addition, pathway analysis points to overlap with neurodegenerative disorders.

Limitations

Owing to the cost and labor-intensive nature of iPSC research, the sample size was small.

Conclusions

Our findings provide insight into the molecular basis of JdVS and can be extrapolated to understand neuropsychiatric decompensation that occurs in subgroups of patients with ASD and other NDDs.

Primary cilia as dynamic and diverse signalling hubs in development and disease

Primary cilia, antenna-like sensory organelles protruding from the surface of most vertebrate cell types, are essential for regulating signalling pathways during development and adult homeostasis. Mutations in genes affecting cilia cause an overlapping spectrum of >30 human diseases and syndromes, the ciliopathies. Given the immense structural and functional diversity of the mammalian cilia repertoire, there is a growing disconnect between patient genotype and associated phenotypes, with variable severity and expressivity characteristic of the ciliopathies as a group. Recent technological developments are rapidly advancing our understanding of the complex mechanisms that control biogenesis and function of primary cilia across a range of cell types and are starting to tackle this diversity. Here, we examine the structural and functional diversity of primary cilia, their dynamic regulation in different cellular and developmental contexts and their disruption in disease.