Severe Developmental Abnormalities Research Articles

Severe Developmental Delay and Behavior Abnormalities in a Patient with De Novo CAMK2B Mutation: A Case Report and Literature Review.

The calcium/calmodulin-dependent protein kinase II-beta (CAMK2B) gene is important for calcium signaling and glutamatergic synapses, which impacts neuroplasticity and learning. Mutations in the CAMK2B gene, which cause autosomal dominant mental retardation 54 (Online Mendelian Inheritance in Man # 617799), can have multisystemic clinical impact. Due to the rarity of CAMK2B mutations at present, case reports about patients with CAMK2B mutations are limited. The present case report describes a patient with CAMK2B-related disorder confirmed by whole exome sequencing and adds to the current information in the literature. We review three case reports in literature with detailed descriptions of patients presenting with mutations in the CAMK2B gene. While there is a broad spectrum of phenotypic presentations, there appears to be an emerging neurobehavioral phenotype. Optimal management of patients will require attention to behavioral issues as well as involvement of neuropsychiatric expertise along with other supports for development and vision abnormalities.

Fdo1, Fkh1, Fkh2 and the Swi6-Mbp1 MBF complex regulate Mcd1 levels to impact eco1 rad61 cell growth in Saccharomyces cerevisiae.

Cohesins promote proper chromosome segregation, gene transcription, genomic architecture, DNA condensation, and DNA damage repair. Mutations in either cohesin subunits or regulatory genes can give rise to severe developmental abnormalities (such as Robert Syndrome and Cornelia de Lange Syndrome) and also are highly correlated with cancer. Despite this, little is known about cohesin regulation. Eco1 (ESCO2/EFO2 in humans) and Rad61 (WAPL in humans) represent two such regulators but perform opposing roles. Eco1 acetylation of cohesin during S phase, for instance, stabilizes cohesin-DNA binding to promote sister chromatid cohesion. On the other hand, Rad61 promotes the dissociation of cohesin from DNA. While Eco1 is essential, ECO1 and RAD61 co-deletion results in yeast cell viability, but only within a limited temperature range. Here, we report that eco1 rad61 cell lethality is due to reduced levels of the cohesin subunit Mcd1. Results from a suppressor screen further reveals that FDO1 deletion rescues the temperature sensitive (ts) growth defects exhibited by eco1 rad61 double mutant cells by increasing Mcd1 levels. Regulation of MCD1 expression, however, appears more complex. Elevated expression of MBP1, which encodes a subunit of the MBF transcription complex, also rescues eco1 rad61 cell growth defects. Elevated expression of SWI6, however, which encodes the Mbp1-binding partner of MBF, exacerbates eco1 rad61 cell growth and also abrogates the Mpb1-dependent rescue. Finally, we identify two additional transcription factors, Fkh1 and Fkh2, that impact MCD1 expression. In combination, these findings provide new insights into the nuanced and multi-faceted transcriptional pathways that impact MCD1 expression.

The structure of TRAF7 coiled-coil trimer provides insight into its function in zebrafish embryonic development.

TRAF7 serves as a crucial intracellular adaptor and E3 ubiquitin ligase involved in signal transduction pathways, contributing to immune responses, tumor progression, and embryonic development. Somatic mutations within the coiled-coil (CC) domain and WD40 repeat domain of TRAF7 could cause brain tumors, while germline pathogenic mutations contribute to severe developmental abnormalities. However, the precise molecular mechanism underlying TRAF7 involvement in embryonic development remains unclear. In this study, we employed zebrafish as an in vivo model system. TRAF7 knock down caused defects in zebrafish embryonic development. We determined the crystal structure of TRAF7 CC domain at 3.3Å resolution and found that the CC region trimerization was essential for TRAF7 functionality during zebrafish embryonic development. Additionally, disease-causing mutations in TRAF7 CC region could impair the trimer formation, consequently impacting early embryonic development of zebrafish. Therefore, our study sheds light on the molecular mechanism of TRAF7 CC trimer formation and its pivotal role in embryonic development.

Trisomies Reorganize Human 3D Genome.

Trisomy is the presence of one extra copy of an entire chromosome or its part in a cell nucleus. In humans, autosomal trisomies are associated with severe developmental abnormalities leading to embryonic lethality, miscarriage or pronounced deviations of various organs and systems at birth. Trisomies are characterized by alterations in gene expression level, not exclusively on the trisomic chromosome, but throughout the genome. Here, we applied the high-throughput chromosome conformation capture technique (Hi-C) to study chromatin 3D structure in human chorion cells carrying either additional chromosome 13 (Patau syndrome) or chromosome 16 and in cultured fibroblasts with extra chromosome 18 (Edwards syndrome). The presence of extra chromosomes results in systematic changes of contact frequencies between small and large chromosomes. Analyzing the behavior of individual chromosomes, we found that a limited number of chromosomes change their contact patterns stochastically in trisomic cells and that it could be associated with lamina-associated domains (LAD) and gene content. For trisomy 13 and 18, but not for trisomy 16, the proportion of compacted loci on a chromosome is correlated with LAD content. We also found that regions of the genome that become more compact in trisomic cells are enriched in housekeeping genes, indicating a possible decrease in chromatin accessibility and transcription level of these genes. These results provide a framework for understanding the mechanisms of pan-genome transcription dysregulation in trisomies in the context of chromatin spatial organization.

Outcomes after HSCT for mucolipidosis II (I-cell disease) caused by novel compound heterozygous GNPTAB mutations.

Mucolipidosis type II (MLII), or I-cell disease, is a rare lysosomal storage disease (LSD) caused by variants in the GNPTAB gene. MLII patients exhibit clinical phenotypes in the prenatal or neonatal stage, such as marked dysmorphic features, cardiac involvement, respiratory symptoms, dysostosis multiplex, severe growth abnormalities, and mental and motor developmental abnormalities. The median age at diagnosis for MLII is 0.7 years, the median survival is 5.0 years, and the median age at death is 1.8 years. No cure for MLII exists. Sanger sequencing of the GNPTAB gene identified the compound heterozygous mutations c.673C > T in exon 7 and c.1090C > T in exon 9, which were novel double heterozygous mutations first reported in China. For the first time, we describe our experience in the use of HSCT for MLII. Our patient underwent HSCT with cells from a 9/10 human leukocyte antigen (HLA)-matched unrelated donor at 12 months of age. Myeloid neutrophil and platelet engraftment occurred on Days 10 and 11, respectively. The patient's limb muscle tension was significantly reduced, and his gross and fine motor skills were improved four months after transplantation. DST(Developmental Screen Test) results showed that the patient's fine motor skills and mental development were improved compared with before HSCT. MLII is a very severe lysosomal storage disease, to date, only 3 cases have been reported on the use of HSCT to treat MLII. Our data show that HSCT is a potential way to prolong the life of patients and improve their quality of life. Due to the lack of comparable data and time, the exact benefit remains unclear in MLII patients. Longer-term follow-up and in-depth prospective studies are indispensable.

The distal femoral epiphysis used as a fetal maturity marker: Implications of extant medical data for bioarcheological analysis

AbstractThe distal epiphysis of the femur is classically reported as a marker of fetal maturity and is thus identified in a bioarcheological context as an indicator that an individual died at or around the time of birth; it thus provides crucial information in the creation of the biological profile and associated burial practices. The aim of the present study was to re‐evaluate this use by investigating an extant sample to assess (i) the age‐related frequencies of both distal femoral and proximal tibial epiphyses and (ii) the influence of factors such as sex, vitality, and morbidity on the maturation of both epiphyses. The study was conducted on medical CT scans acquired in utero and ex utero between 2008 and 2017 in the hospital of Marseille (France). The final sample included 248 individuals aged between 26 and 42 completed gestational weeks (GW). Based on the results obtained in this study, 11% of the individuals from the sample aged between 26 and 33 completed GW had already developed a distal femoral epiphysis, whereas individuals aged between 38 and 42 GW had already developed both femoral and tibial epiphyses. According to these observations and current obstetrical practice, this maturation indicator cannot therefore be considered a precise estimator of whether a fetus is at term or not in an archeological context. Similarly, no delayed ossification was found among individuals who did not survive to 42 GW, or among those with severe developmental abnormalities, which does not support the hypothesis that delayed epiphysis maturation of the distal femur may be a morbidity marker for this age group in past populations.

A novel de novo variant in CASK causes a severe neurodevelopmental disorder that masks the phenotype of a novel de novo variant in EEF2.

We report a 9-year-old Spanish boy with severe psychomotor developmental delay, short stature, microcephaly and abnormalities of the brain morphology, including cerebellar atrophy. Whole-exome sequencing (WES) uncovered two novel de novo variants, a hemizygous variant in CASK (Calcium/Calmodulin Dependent Serine Protein Kinase) and a heterozygous variant in EEF2 (Eukaryotic Translation Elongation Factor 2). CASK gene encodes the peripheral plasma membrane protein CASK that is a scaffold protein located at the synapses in the brain. The c.2506-6 A > G CASK variant induced two alternative splicing events that account for the 80% of the total transcripts, which are likely to be degraded by NMD. Pathogenic variants in CASK have been associated with severe neurological disorders such as mental retardation with or without nystagmus also called FG syndrome 4 (FGS4), and intellectual developmental disorder with microcephaly and pontine and cerebellar hypoplasia (MICPCH). Heterozygous variants in EEF2, which encodes the elongation factor 2 (eEF2), have been associated to Spinocerebellar ataxia 26 (SCA26) and more recently to a childhood-onset neurodevelopmental disorder with benign external hydrocephalus. The yeast model system used to investigate the functional consequences of the c.34 A > G EEF2 variant supported its pathogenicity by demonstrating it affects translational fidelity. In conclusion, the phenotype associated with the CASK variant is more severe and masks the milder phenotype of EEF2 variant.

A Case Report of Solitary Median Maxillary Central Incisor Reported in Tehsil Headquarter Hospital, Gujjar Khan, Pakistan

Solitary median maxillary central incisor is a rare dental anomaly and a complex disorder consisting of multiple mainly midline defects of development. In SMMCI, only one central incisor is present, and it develops exactly at the midline. It results from unknown factors(s) operating in utero. Early diagnosis and recognition of SMMCI are important for all practicing dentists, as it may be a sign of other severe congenital or developmental abnormalities. This case report discusses important aspects of SMMCI and presents a clinical case of a 2-year-old female patient of single median maxillary central incisor with missing maxillary and mandibular frena, along with brain growth retardation in Tehsil Headquarter Hospital, Gujjar Khan, Pakistan. Aligned with the literature early diagnosis and correction of SMMCI is of prime importance as the condition is associated with developmental problems. Moreover, the case should be managed by a multidisciplinary team of health professionals to ensure optimum health-related outcomes. Keywords: Solitary, median, maxillary, central incisor, case report

Plastic leachate-induced toxicity during sea urchin embryonic development: Insights into the molecular pathways affected by PVC

Microplastics are now polluting all seas and, while studies have found numerous negative interactions between plastic pollution and marine animals, the effects on embryonic development are poorly understood. A potentially important source of developmental ecotoxicity comes from chemicals leached from plastic particles to the marine environment. Here we investigate the effects of leachates from new and beach-collected pellets on the embryonic and larval development of the sea urchin Strongylocentrotus purpuratus and demonstrate that exposure of developing embryos to these leachates elicits severe, consistent and treatment-specific developmental abnormalities including radialisation of the embryo and malformation of the skeleton, neural and immune cells. Using a multi-omics approach we define the developmental pathways disturbed upon exposure to PVC leachates and provide a mechanistic view that pinpoints cellular redox stress and energy production as drivers of phenotypic abnormalities following exposure to PVC leachates. Analysis of leachates identified high concentrations of zinc that are the likely cause of these observed defects. Our findings point to clear and specific detrimental effects of marine plastic pollution on the development of echinoderms, demonstrating that chemicals leached from plastic particles into sea water can produce strong developmental abnormalities via specific pathways, and therefore have the potential to impact on a wide range of organisms.

The non-catalytic role of DNA polymerase epsilon in replication initiation in human cells

DNA polymerase epsilon (PolE) in an enzyme essential for DNA replication. Deficiencies and mutations in PolE cause severe developmental abnormalities and cancers. Paradoxically, the catalytic domain of yeast PolE catalytic subunit is dispensable for survival, and its non-catalytic essential function is linked with replicative helicase (CMG) assembly. Less is known about the PolE role in replication initiation in human cells. Here we use an auxin-inducible degron system to study the effect of POLE1 depletion on replication initiation in U2OS cells. POLE1-depleted cells were able to assemble CMG helicase and initiate DNA synthesis that failed shortly after. Expression of POLE1 non-catalytic domain rescued this defect resulting in slow, but continuous DNA synthesis. We propose a model where in human U2OS cells POLE1/POLE2 are dispensable for CMG assembly, but essential during later steps of replication initiation. Our study provides some insights into the role of PolE in replication initiation in human cells.

Allan-Herndon-Dudley syndrome: Report of a novel pathogenic variant in MCT8 gene

X-linked MCT8 mutations cause Allan-Herndon-Dudley syndrome (AHDS) characterized by severe developmental delay and specific thyroid function abnormality. The report describes a 1 year-old boy with severe developmental delay, truncal hypotonia, quadriparesis (spastic), dystonia, and thyroid function abnormality (high free T3, low reverse T3, low free T4, and normal TSH) suggesting a form of impaired thyroid hormone sensitivity, namely, AHDS. WES analysis yielded novel hemizygous single-base pair duplication in exon 1 of MCT8 gene, validated by Sanger sequencing. MRI revealed generalized demyelination with poor gray and white matter differentiation and loss of brain volume. Indirect markers revealed thyrotoxicosis in some peripheral tissues. Having high index of suspicion for this rare disorder and plausible benefit of inclusion of free T3 assay in initial evaluation of infants and children with idiopathic developmental delay are emphasized. Amelioration of thyrotoxic features with tri-iodothyroacetic acid likely benefits patients at all ages. Neurodevelopmental improvement has been observed in those who received tri-iodoacetic acid early, which is being currently investigated.

Mechanisms of Zika astrocyte infection and neuronal toxicity.

Zika virus (ZIKV) has become an epidemic in several countries and was declared a major public health issue by the WHO. Although ZIKV infection is asymptomatic or shows mild fever-related symptoms in most people, the virus can be transmitted from a pregnant mother to the fetus, resulting in severe brain developmental abnormalities, including microcephaly. Multiple groups have identified developmental neuronal and neuronal progenitor compromise during ZIKV infection within the fetal brain, but little is known about whether ZIKV could infect human astrocytes and its effect on the developing brain. Thus, our objective was to determine astrocyte ZiKV infection in a developmental-dependent manner. We analyze infection of pure cultures of astrocytes and mixed cultures of neurons and astrocytes in response to ZIKV using plaque assays, confocal, and electron microscopy to identify infectivity, ZIKV accumulation and intracellular distribution as well as apoptosis and interorganelle dysfunction. Here, we demonstrated that ZIKV enters, infects, replicates, and accumulates in large quantities in human fetal astrocytes in a developmental-dependent manner. Astrocyte infection and intracellular viral accumulation resulted in neuronal apoptosis, and we propose astrocytes are a ZIKV reservoir during brain development. Our data identify astrocytes in different stages of development as major contributors to the devastating effects of ZIKV in the developing brain.

Phenylalanine hydroxylase mRNA rescues the phenylketonuria phenotype in mice.

Phenylketonuria (PKU) is an inborn error of metabolism caused by a deficiency in functional phenylalanine hydroxylase (PAH), resulting in accumulation of phenylalanine (Phe) in patients’ blood and organs. Affected patients encounter severe developmental delay, neurological deficits, and behavioral abnormalities when not treated. Early diagnosis and treatment are extremely important; newborn screening programs have been implemented in most countries to ensure early identification of patients with PKU. Despite available treatment options, several challenges remain: life-long adherence to a strict diet, approval of some medications for adults only, and lack of response to these therapies in a subpopulation of patients. Therefore, there is an urgent need for treatment alternatives. An mRNA-based approach tested in PKU mice showed a fast reduction in the accumulation of Phe in serum, liver and brain, the most significant organ affected. Repeated injections of LNP-formulated mouse PAH mRNA rescued PKU mice from the disease phenotype for a prolonged period of time. An mRNA-based approach could improve the quality of life tremendously in PKU patients of all ages by replacing standard-of-care treatments.

G1-Cyclin2 (Cln2) promotes chromosome hypercondensation in eco1/ctf7 rad61 null cells during hyperthermic stress in Saccharomyces cerevisiae.

Eco1/Ctf7 is a highly conserved acetyltransferase that activates cohesin complexes and is critical for sister chromatid cohesion, chromosome condensation, DNA damage repair, nucleolar integrity, and gene transcription. Mutations in the human homolog of ECO1 (ESCO2/EFO2), or in genes that encode cohesin subunits, result in severe developmental abnormalities and intellectual disabilities referred to as Roberts syndrome and Cornelia de Lange syndrome, respectively. In yeast, deletion of ECO1 results in cell inviability. Codeletion of RAD61 (WAPL in humans), however, produces viable yeast cells. These eco1 rad61 double mutants, however, exhibit a severe temperature-sensitive growth defect, suggesting that Eco1 or cohesins respond to hyperthermic stress through a mechanism that occurs independent of Rad61. Here, we report that deletion of the G1 cyclin CLN2 rescues the temperature-sensitive lethality otherwise exhibited by eco1 rad61 mutant cells, such that the triple mutant cells exhibit robust growth over a broad range of temperatures. While Cln1, Cln2, and Cln3 are functionally redundant G1 cyclins, neither CLN1 nor CLN3 deletions rescue the temperature-sensitive growth defects otherwise exhibited by eco1 rad61 double mutants. We further provide evidence that CLN2 deletion rescues hyperthermic growth defects independent of START and impacts the state of chromosome condensation. These findings reveal novel roles for Cln2 that are unique among the G1 cyclin family and appear critical for cohesin regulation during hyperthermic stress.

MEDB-12. Severe developmental abnormalities and proliferative cerebellar lesions induced by combined activity of Wnt signalling and loss of SMARCA4

Almost all medulloblastomas (MB) of the WNT subgroup are characterized by hotspot mutations in CTNNB1, and mouse models have convincingly demonstrated the tumor-initiating role of these mutations as well as the tumor origin in the dorsal brain stem. Around 20 % of WNT MB additionally carry SMARCA4mutations, but the functional role of these alterations is mostly unknown. We therefore amended previously described Blbp-cre::Ctnnb1(ex3)Fl/+mice by the introduction of a floxed Smarca4 allele. In contrast to existing literature, Blbp-cre::Ctnnb1(ex3)Fl/+ mice had a maximum life span of only 17 days, even after breeding into two different genetic backgrounds (C57BL/6J and 129S2/Sv). The mice displayed a severe developmental phenotype including a thinned cerebral cortex, hydrocephalus, missing cerebellar foliation and layering as well as non-proliferative cell accumulations in brain stem and cerebellum. An additional homozygous loss of SMARCA4 even resulted in prenatal death for most mice and caused big proliferative lesions in the cerebellum at embryonal day 14.5. These lesions appear to originate from SOX2-positive progenitor cells in the cerebellar ventricular zone. In a next experiment, cells isolated from this region will be characterized in vitro and will be transplanted orthotopically to evaluate their neoplastic potential in vivo. Altogether, we hope to elucidate how a loss of SMARCA4 and mutations of Ctnnb1 cooperate during hindbrain development and tumor formation within this region.

Age-related neurodegeneration and cognitive impairments of NRMT1 knockout mice are preceded by misregulation of RB and abnormal neural stem cell development

N-terminal methylation is an important posttranslational modification that regulates protein/DNA interactions and plays a role in many cellular processes, including DNA damage repair, mitosis, and transcriptional regulation. Our generation of a constitutive knockout mouse for the N-terminal methyltransferase NRMT1 demonstrated its loss results in severe developmental abnormalities and premature aging phenotypes. As premature aging is often accompanied by neurodegeneration, we more specifically examined how NRMT1 loss affects neural pathology and cognitive behaviors. Here we find that Nrmt1−/− mice exhibit postnatal enlargement of the lateral ventricles, age-dependent striatal and hippocampal neurodegeneration, memory impairments, and hyperactivity. These morphological and behavior abnormalities are preceded by alterations in neural stem cell (NSC) development. Early expansion and differentiation of the quiescent NSC pool in Nrmt1−/− mice is followed by its subsequent depletion and many of the resulting neurons remain in the cell cycle and ultimately undergo apoptosis. These cell cycle phenotypes are reminiscent to those seen with loss of the NRMT1 target retinoblastoma protein (RB). Accordingly, we find misregulation of RB phosphorylation and degradation in Nrmt1−/− mice, and significant de-repression of RB target genes involved in cell cycle. We also identify novel de-repression of Noxa, an RB target gene that promotes apoptosis. These data identify Nα-methylation as a novel regulatory modification of RB transcriptional repression during neurogenesis and indicate that NRMT1 and RB work together to promote NSC quiescence and prevent neuronal apoptosis.

XRCC3 loss leads to midgestational embryonic lethality in mice

RAD51 paralogs are key components of the homologous recombination (HR) machinery. Mouse mutants have been reported for four of the canonical RAD51 paralogs, and each of these mutants exhibits embryonic lethality, although at different gestational stages. However, the phenotype of mice deficient in the fifth RAD51 paralog, XRCC3, has not been reported. Here we report that Xrcc3 knockout mice exhibit midgestational lethality, with mild phenotypes beginning at about E8.25 but severe developmental abnormalities evident by E9.0–9.5. The most obvious phenotypes are small size and a failure of the embryo to turn to a fetal position. A knockin mutation at a key ATPase residue in the Walker A box results in embryonic lethality at a similar stage. Death of knockout mice can be delayed a few days for some embryos by homozygous or heterozygous Trp53 mutation, in keeping with an important role for XRCC3 in promoting genome integrity. Given that XRCC3 is a unique member of one of two RAD51 paralog complexes with RAD51C, these results demonstrate that both RAD51 paralog complexes are required for mouse development.

TNPO2 variants associate with human developmental delays, neurologic deficits, and dysmorphic features and alter TNPO2 activity in Drosophila

Transportin-2 (TNPO2) mediates multiple pathways including non-classical nucleocytoplasmic shuttling of >60 cargoes, such as developmental and neuronal proteins. We identified 15 individuals carrying de novo coding variants in TNPO2 who presented with global developmental delay (GDD), dysmorphic features, ophthalmologic abnormalities, and neurological features. To assess the nature of these variants, functional studies were performed in Drosophila. We found that fly dTnpo (orthologous to TNPO2) is expressed in a subset of neurons. dTnpo is critical for neuronal maintenance and function as downregulating dTnpo in mature neurons using RNAi disrupts neuronal activity and survival. Altering the activity and expression of dTnpo using mutant alleles or RNAi causes developmental defects, including eye and wing deformities and lethality. These effects are dosage dependent as more severe phenotypes are associated with stronger dTnpo loss. Interestingly, similar phenotypes are observed with dTnpo upregulation and ectopic expression of TNPO2, showing that loss and gain of Transportin activity causes developmental defects. Further, proband-associated variants can cause more or less severe developmental abnormalities compared to wild-type TNPO2 when ectopically expressed. The impact of the variants tested seems to correlate with their position within the protein. Specifically, those that fall within the RAN binding domain cause more severe toxicity and those in the acidic loop are less toxic. Variants within the cargo binding domain show tissue-dependent effects. In summary, dTnpo is an essential gene in flies during development and in neurons. Further, proband-associated de novo variants within TNPO2 disrupt the function of the encoded protein. Hence, TNPO2 variants are causative for neurodevelopmental abnormalities.

De novo and bi-allelic variants in AP1G1 cause neurodevelopmental disorder with developmental delay, intellectual disability, and epilepsy

Adaptor protein (AP) complexes mediate selective intracellular vesicular trafficking and polarized localization of somatodendritic proteins in neurons. Disease-causing alleles of various subunits of AP complexes have been implicated in several heritable human disorders, including intellectual disabilities (IDs). Here, we report two bi-allelic (c.737C>A [p.Pro246His] and c.1105A>G [p.Met369Val]) and eight de novo heterozygous variants (c.44G>A [p.Arg15Gln], c.103C>T [p.Arg35Trp], c.104G>A [p.Arg35Gln], c.229delC [p.Gln77Lys∗11], c.399_400del [p.Glu133Aspfs∗37], c.747G>T [p.Gln249His], c.928-2A>C [p.?], and c.2459C>G [p.Pro820Arg]) in AP1G1, encoding gamma-1 subunit of adaptor-related protein complex 1 (AP1γ1), associated with a neurodevelopmental disorder (NDD) characterized by mild to severe ID, epilepsy, and developmental delay in eleven families from different ethnicities. The AP1γ1-mediated adaptor complex is essential for the formation of clathrin-coated intracellular vesicles. In silico analysis and 3D protein modeling simulation predicted alteration of AP1γ1 protein folding for missense variants, which was consistent with the observed altered AP1γ1 levels in heterologous cells. Functional studies of the recessively inherited missense variants revealed no apparent impact on the interaction of AP1γ1 with other subunits of the AP-1 complex but rather showed to affect the endosome recycling pathway. Knocking out ap1g1 in zebrafish leads to severe morphological defect and lethality, which was significantly rescued by injection of wild-type AP1G1 mRNA and not by transcripts encoding the missense variants. Furthermore, microinjection of mRNAs with de novo missense variants in wild-type zebrafish resulted in severe developmental abnormalities and increased lethality. We conclude that de novo and bi-allelic variants in AP1G1 are associated with neurodevelopmental disorder in diverse populations.

Isoflucypram cardiovascular toxicity in zebrafish (Danio rerio)

Isoflucypram belongs to the new generation of succinate dehydrogenase inhibitor (SDHI) fungicides that are commonly used in crop fungal disease control. Evidence indicates that isoflucypram poses a potential risk to aquatic organisms. However, the effects of isoflucypram during early embryogenesis are not fully understood. In the present study, zebrafish embryos were exposed to 0.025, 0.25, or 2.5 μM isoflucypram for three days. Isoflucypram caused severe developmental abnormalities (yolk sac edema, pericardial edema, and blood clotting clustering), hatching delay, and decreased heart rates in zebrafish. The expression levels of cardiac-specific genes (nkx2.5, myh7, myl7, and myh6) and erythropoiesis-related genes (gata1a, hbbe1, hbbe2, and alas2) were disrupted after isoflucypram exposure. Furthermore, enrichment analysis indicated that most of the differentially expressed genes (DEGs) were enriched in heart development or hemopoiesis processes. Overall, these findings suggest that exposure to isoflucypram is associated with developmental and cardiovascular toxicity in zebrafish.