Biology subjects

van der Linde, H. C.

Publications and source records attributed to van der Linde, H. C..

5 recordsLinked to original sources

bioRxiv2025

TFEB-depletion rescues TMEM106B-related myelin defects in zebrafish

Lysosomal transmembrane protein TMEM106B is genetically and neuropathologically implicated in a range of neurodegenerative diseases. Unexpectedly, the recurrent de novo TMEM106B variant p.(Asp252Asn) causes a hypomyelinating disorder. TMEM106B controls lysosomal positioning in neurons, but its role in white matter health is not fully understood. To study the role of TMEM106B in myelination in vivo, we mutated zebrafish tmem106ba and tmem106bb homologs. In vivo brain imaging in larvae deficient for both homologs (tmem106bdm) showed more, smaller lysosomes, accompanied by reduced myelin content and shorter myelin sheaths. Oligodendrocytes in tmem106bdm exhibited more lysosomes in the perinuclear region. We next genome-edited the pathogenic p.(Asp252Asn) variant into the zebrafish genome and showed that it acts dominant-negatively on myelination and on lysosomal clustering around the nucleus in oligodendrocytes. As lysosomal peri-nuclear positioning modulates mTOR-signaling, and downstream transcription factor EB (TFEB) inhibits myelination, we next investigated whether there is a genetic interaction between TMEM106B and TFEB. Indeed, deficient myelination in tmem106bdm larvae, but not altered lysosomal clustering, was restored by loss of Tfeb in triple mutant larvae. Our work elucidates that TMEM106B modulates myelination by a TFEB-dependent pathway. This implicates the TFEB pathway in myelin development and white matter health and suggests that modulating TFEB could be a therapeutic target in white matter disorders.

genetics↗

bioRxiv2024

The non-canonical thioreductase TMX2 is essential for neuronal survival during embryonic brain development

Biallelic variants in thioredoxin-related transmembrane 2 protein (TMX2) can cause a brain malformation of cortical development (MCD), characterized by primary microcephaly, polymicrogyria and pachygyria by an unknown mechanism. To better understand and visualize how TMX2 loss disrupts brain development in vivo we investigated the function of TMX2, using the zebrafish embryo as a model system. We generated zebrafish deficient for TMX2 ortholog tmx2b, which during the first 2 days post fertilization (dpf) showed normal behavioral activity and brain developmental hallmarks. From 3 dpf onwards however, tmx2b mutants failed to exhibit locomotor activity, which was accompanied by cell death primarily in the brain, but not in other organs or in the spinal cord. Strikingly, cell death in tmx2b mutants occurs specifically in newborn neurons within a [~]1.5-hour timeframe, whereas neuronal progenitor and other glial cells are preserved, and could be suppressed by inhibiting neuronal activity. In vivo GCaMP6s calcium imaging showed a persistent [~]2-fold increase in calcium in neurons after the onset of cell death. This suggests that calcium homeostasis underlies the tmx2b mutant brain phenotype. Altogether, our results indicate that TMX2 is an evolutionary conserved, protective regulator essential specifically for newborn neurons to survive after their differentiation in the vertebrate embryonic brain.

developmental biology↗

bioRxiv2021

Comprehensive multi-omics integration identifies differentially active enhancers during human brain development with clinical relevance

BackgroundNon-coding regulatory elements (NCREs), such as enhancers, play a crucial role in gene regulation and genetic aberrations in NCREs can lead to human disease, including brain disorders. The human brain is complex and can be affected by numerous disorders; many of these are caused by genetic changes, but a multitude remain currently unexplained. Understanding NCREs acting during brain development has the potential to shed light on previously unrecognised genetic causes of human brain disease. Despite immense community-wide efforts to understand the role of the non-coding genome and NCREs, annotating functional NCREs remains challenging. ResultsHere we performed an integrative computational analysis of virtually all currently available epigenome data sets related to human fetal brain. Our in-depth analysis unravels 39,709 differentially active enhancers (DAEs) that show dynamic epigenomic rearrangement during early stages of human brain development, indicating likely biological function. Many of these DAEs are linked to clinically relevant genes, and functional validation of selected DAEs in cell models and zebrafish confirms their role in gene regulation. Compared to enhancers without dynamic epigenomic rearrangement, these regions are subjected to higher sequence constraints in humans, have distinct sequence characteristics and are bound by a distinct transcription factor landscape. DAEs are enriched for GWAS loci for brain related traits and for genetic variation found in individuals with neurodevelopmental disorders, including autism. ConclusionOur compendium of high-confidence enhancers will assist in deciphering the mechanism behind developmental genetics of the human brain and will be relevant to uncover missing heritability in human genetic brain disorders.

genomics↗

bioRxiv2019

Loss of UGP2 in brain leads to a severe epileptic encephalopathy, emphasizing that bi-allelic isoform specific start-loss mutations of essential genes can cause genetic diseases

Developmental and/or epileptic encephalopathies (DEEs) are a group of devastating genetic disorders, resulting in early onset, therapy resistant seizures and developmental delay. Here we report on 12 individuals from 10 families presenting with a severe form of intractable epilepsy, severe developmental delay, progressive microcephaly and visual disturbance. Whole exome sequencing identified a recurrent, homozygous variant (chr2:64083454A>G) in the essential UDP-glucose pyrophosphorylase (UGP2) gene in all probands. This rare variant results in a tolerable Met12Val missense change of the longer UGP2 protein isoform but causes a disruption of the start codon of the shorter isoform. We show that the absence of the shorter isoform leads to a reduction of functional UGP2 enzyme in brain cell types, leading to altered glycogen metabolism, upregulated unfolded protein response and premature neuronal differentiation, as modelled during pluripotent stem cell differentiation in vitro. In contrast, the complete lack of all UGP2 isoforms leads to differentiation defects in multiple lineages in human cells. Reduced expression of Ugp2a/Ugp2b in vivo in zebrafish mimics visual disturbance and mutant animals show a behavioral phenotype. Our study identifies a recurrent start codon mutation in UGP2 as a cause of a novel autosomal recessive DEE. Importantly, it also shows that isoform specific start-loss mutations causing expression loss of a tissue relevant isoform of an essential protein can cause a genetic disease, even when an organism-wide protein absence is incompatible with life. We provide additional examples where a similar disease mechanism applies.

genetics↗

bioRxiv2018

Reverse genetic screen reveals that Il34 facilitates yolk sac macrophage distribution and seeding of the brain

Microglia are brain resident macrophages, which have specialized functions important in brain development and in disease. They colonize the brain in early embryonic stages, but few factors that drive the migration of yolk sac macrophages into the embryonic brain, or regulate their acquisition of specialized properties are currently known.\n\nHere, we present a CRISPR/Cas9-based in vivo reverse genetic screening pipeline to identify new regulators important for microglia development using zebrafish. Zebrafish larvae are particularly suitable due to their external development, transparency, high fecundity and conserved microglia features. We targeted putative microglia regulators, including signature genes and non-cell autonomous factors, by Cas9/gRNA-complex injections, followed by neutral red-based visualization of microglia. Microglia were quantified automatically in 3-day-old larvae using a software tool we called SpotNGlia. We identified that loss of function of the zebrafish homolog of the colony stimulating factor 1 receptor (CSF1R) ligand IL34, caused strongly reduced microglia numbers in early development. Previous studies on the role of the IL34 on microglia development in vivo were ambiguous. Our data, and a concurrent paper, show that in zebrafish, il34 is required during the earliest seeding of the brain by microglia progenitors. Our data also indicate that Il34 is required for distribution to other organs.\n\nPreviously, we showed that csf1ra and csf1rb double mutant zebrafish have no microglia. As there is a moderate effect of il34 on microglia development, relative to the effect csf1r, additional Csf1r-dependent signalling may be needed for establishment of the microglia network. In all, we identified il34 as a modifier of microglia colonization, by affecting distribution of yolk sac macrophages to target organs, validating our reverse genetic screening pipeline in zebrafish which can be used for the identification of additional regulators of microglia development.

developmental biology↗