Molecular Genetics of Microcephaly Primary Hereditary: An Overview

Burden of Rare Copy Number Variants in Microcephaly: A Brazilian Cohort of 185 Microcephalic Patients and Review of the Literature

Microcephaly presents heterogeneous genetic etiology linked to several neurodevelopmental disorders (NDD). Copy number variants (CNVs) are a causal mechanism of microcephaly whose investigation is a crucial step for unraveling its molecular basis. Our purpose was to investigate the burden of rare CNVs in microcephalic individuals and to review genes and CNV syndromes associated with microcephaly. We performed chromosomal microarray analysis (CMA) in 185 Brazilian patients with microcephaly and evaluated microcephalic patients carrying < 200 kb CNVs documented in the DECIPHER database. Additionally, we reviewed known genes and CNV syndromes causally linked to microcephaly through the PubMed, OMIM, DECIPHER, and ClinGen databases. Rare clinically relevant CNVs were detected in 39 out of the 185 Brazilian patients investigated by CMA (21%). In 31 among the 60 DECIPHER patients carrying < 200 kb CNVs, at least one known microcephaly gene was observed. Overall, four gene sets implicated in microcephaly were disclosed: known microcephaly genes; genes with supporting evidence of association with microcephaly; known macrocephaly genes; and novel candidates, including OTUD7A, BBC3, CNTN6, and NAA15. In the review, we compiled 957 known microcephaly genes and 58 genomic CNV loci, comprising 13 duplications and 50 deletions, which have already been associated with clinical findings including microcephaly. We reviewed genes and CNV syndromes previously associated with microcephaly, reinforced the high CMA diagnostic yield for this condition, pinpointed novel candidate loci linked to microcephaly deserving further evaluation, and provided a useful resource for future research on the field of neurodevelopment.

Second report of TEDC1-related microcephaly caused by a novel biallelic mutation in an Iranian consanguineous family

BACKGROUND

Primary autosomal recessive microcephaly (MCPH) is a rare developmental disorder characterized by cognitive impairment, delayed neurodevelopment, and reduced brain size. It is a genetically heterogeneous condition, and several genes have been identified as associated with MCPH.

METHODS AND RESULTS

In this study, we utilized whole-exome sequencing (WES) to identify disease-causing variations in two brothers from an Iranian family affected by MCPH, who had consanguineous parents. In the patients, we detected a novel homozygous missense mutation (c.806A > G, p.Gln269Arg) in the TEDC1 gene in one of the patients. Co-segregation analysis using Sanger sequencing confirmed that this variant was inherited from parents. The identified variant was evaluated for its pathogenicity and novelty using various databases. Additionally, bioinformatics tools were employed to predict the three-dimensional structure of the mutant TEDC1 protein.

CONCLUSIONS

This study presents the second documented report of a mutation in the TEDC1 gene associated with MCPH. The identification of this novel biallelic mutation as a causative factor for MCPH in the proband further underscores the utility of genetic testing techniques, such as WES, as reliable diagnostic tools for individuals with this condition.

Mutations in abnormal spindle disrupt temporal transcription factor expression and trigger immune responses in the Drosophila brain

The coordination of cellular behaviors during neurodevelopment is critical for determining the form, function, and size of the central nervous system (CNS). Mutations in the vertebrate Abnormal Spindle-Like, Microcephaly Associated (ASPM) gene and its Drosophila melanogaster ortholog abnormal spindle (asp) lead to microcephaly (MCPH), a reduction in overall brain size whose etiology remains poorly defined. Here, we provide the neurodevelopmental transcriptional landscape for a Drosophila model for autosomal recessive primary microcephaly-5 (MCPH5) and extend our findings into the functional realm to identify the key cellular mechanisms responsible for Asp-dependent brain growth and development. We identify multiple transcriptomic signatures, including new patterns of coexpressed genes in the developing CNS. Defects in optic lobe neurogenesis were detected in larval brains through downregulation of temporal transcription factors (tTFs) and Notch signaling targets, which correlated with a significant reduction in brain size and total cell numbers during the neurogenic window of development. We also found inflammation as a hallmark of asp mutant brains, detectable throughout every stage of CNS development, which also contributes to the brain size phenotype. Finally, we show that apoptosis is not a primary driver of the asp mutant brain phenotypes, further highlighting an intrinsic Asp-dependent neurogenesis promotion mechanism that is independent of cell death. Collectively, our results suggest that the etiology of the asp mutant brain phenotype is complex and that a comprehensive view of the cellular basis of the disorder requires an understanding of how multiple pathway inputs collectively determine tissue size and architecture.

DNA damage and repair: underlying mechanisms leading to microcephaly

DNA-damaging agents and endogenous DNA damage constantly harm genome integrity. Under genotoxic stress conditions, the DNA damage response (DDR) machinery is crucial in repairing lesions and preventing mutations in the basic structure of the DNA. Different repair pathways are implicated in the resolution of such lesions. For instance, the non-homologous DNA end joining and homologous recombination pathways are central cellular mechanisms by which eukaryotic cells maintain genome integrity. However, defects in these pathways are often associated with neurological disorders, indicating the pivotal role of DDR in normal brain development. Moreover, the brain is the most sensitive organ affected by DNA-damaging agents compared to other tissues during the prenatal period. The accumulation of lesions is believed to induce cell death, reduce proliferation and premature differentiation of neural stem and progenitor cells, and reduce brain size (microcephaly). Microcephaly is mainly caused by genetic mutations, especially genes encoding proteins involved in centrosomes and DNA repair pathways. However, it can also be induced by exposure to ionizing radiation and intrauterine infections such as the Zika virus. This review explains mammalian cortical development and the major DNA repair pathways that may lead to microcephaly when impaired. Next, we discuss the mechanisms and possible exposures leading to DNA damage and p53 hyperactivation culminating in microcephaly.

Diagnostic yield and novel candidate genes for neurodevelopmental disorders by exome sequencing in an unselected cohort with microcephaly

OBJECTIVES

Microcephaly is caused by reduced brain volume and most usually associated with a variety of neurodevelopmental disorders (NDDs). To provide an overview of the diagnostic yield of whole exome sequencing (WES) and promote novel candidates in genetically unsolved families, we studied the clinical and genetic landscape of an unselected Chinese cohort of patients with microcephaly.

METHODS

We performed WES in an unselected cohort of 103 NDDs patients with microcephaly as one of the features. Full evaluation of potential novel candidate genes was applied in genetically undiagnosed families. Functional validations of selected variants were conducted in cultured cells. To augment the discovery of novel candidates, we queried our genomic sequencing data repository for additional likely disease-causing variants in the identified candidate genes.

RESULTS

In 65 families (63.1%), causative sequence variants (SVs) and clinically relevant copy number variants (CNVs) with a pathogenic or likely pathogenic (P/LP) level were identified. By incorporating coverage analysis to WES, a pathogenic or likely pathogenic CNV was detected in 15 families (16/103, 15.5%). In another eight families (8/103, 7.8%), we identified variants in newly reported gene (CCND2) and potential novel neurodevelopmental disorders /microcephaly candidate genes, which involved in cell cycle and division (PWP2, CCND2), CDC42/RAC signaling related actin cytoskeletal organization (DOCK9, RHOF), neurogenesis (ELAVL3, PPP1R9B, KCNH3) and transcription regulation (IRF2BP1). By looking into our data repository of 5066 families with NDDs, we identified additional two cases with variants in DOCK9 and PPP1R9B, respectively.

CONCLUSION

Our results expand the morbid genome of monogenic neurodevelopmental disorders and support the adoption of WES as a first-tier test for individuals with microcephaly.

An integrative systems biology strategy to support the development of adverse outcome pathways (AOPs): a case study on radiation-induced microcephaly

Adverse Outcome Pathways (AOPs) are useful tools for assessing the potential risks associated with exposure to various stressors, including chemicals and environmental contaminants. They provide a framework for understanding the causal relationships between different biological events that can lead to adverse outcomes (AO). However, developing an AOP is a challenging task, particularly in identifying the molecular initiating events (MIEs) and key events (KEs) that constitute it. Here, we propose a systems biology strategy that can assist in the development of AOPs by screening publicly available databases, literature with the text mining tool AOP-helpFinder, and pathway/network analyses. This approach is straightforward to use, requiring only the name of the stressor and adverse outcome to be studied. From this, it quickly identifies potential KEs and literature providing mechanistic information on the links between the KEs. The proposed approach was applied to the recently developed AOP 441 on radiation-induced microcephaly, resulting in the confirmation of the KEs that were already present and identification of new relevant KEs, thereby validating the strategy. In conclusion, our systems biology approach represents a valuable tool to simplify the development and enrichment of Adverse Outcome Pathways (AOPs), thus supporting alternative methods in toxicology.

Microcephaly, Short Stature, Intellectual Disability, Speech Absence and Cataract Are Associated with Novel Bi-Allelic Missense Variant in RTTN Gene: A Seckel Syndrome Case Report

The RTTN gene encodes centriole biogenesis, replication, symmetry and cohesion, basal body organization and has recently been associated with the appearance of microcephaly syndromes. RTTN-related neurological defects including microcephaly, intellectual disability, congenital dwarfism, ophthalmic manifestations, and epilepsy are mainly due to abnormal brain development pathways and loss-of-function protein mutations. We present a consanguineous Pakistani family clinically suspected of Seckel syndrome with severe microcephaly, severe intellectual disability, short stature, absence of speech, pointed nose, narrow face and bilateral cataract in two siblings residing in the suburbs of Islamabad. Forty cases of Seckel syndrome have been reported to date in the literature due to mutations in the ATR, TRAIP, RBBP8, NSMCE2, NIN, CENPJ, DNA2, CEP152 and CEP63 genes. The objective of the study was to perform a clinical diagnosis, genetic analysis, and pathophysiology of Seckel syndrome in the proband. Whole-exome sequencing discovered NM_173630.4: c.57G > T(pGlu19Asp) missense variant in exon 2 of the RTTN gene that co-segregates in the family. This novel variant, to the best of our knowledge, is pathogenic and with autosomal recessive inheritance expressed as Seckel syndrome in the affected members of the family. The present study has expanded the genetic knowledge of novel RTTN gene variants associated with Seckel syndrome and has broadened its phenotype spectrum in the Pakistani population, which comprises diverse ethnicities. We hope that our study will open new horizons for individual molecular diagnosis and therapeutics to improve the life of patients with this congenital syndrome.

Neurodevelopmental disorders, like cancer, are connected to impaired chromatin remodelers, PI3K/mTOR, and PAK1-regulated MAPK

Neurodevelopmental disorders (NDDs) and cancer share proteins, pathways, and mutations. Their clinical symptoms are different. However, individuals with NDDs have higher probabilities of eventually developing cancer. Here, we review the literature and ask how the shared features can lead to different medical conditions and why having an NDD first can increase the chances of malignancy. To explore these vital questions, we focus on dysregulated PI3K/mTOR, a major brain cell growth pathway in differentiation, and MAPK, a critical pathway in proliferation, a hallmark of cancer. Differentiation is governed by chromatin organization, making aberrant chromatin remodelers highly likely agents in NDDs. Dysregulated chromatin organization and accessibility influence the lineage of specific cell brain types at specific embryonic development stages. PAK1, with pivotal roles in brain development and in cancer, also regulates MAPK. We review, clarify, and connect dysregulated pathways with dysregulated proliferation and differentiation in cancer and NDDs and highlight PAK1 role in brain development and MAPK regulation. Exactly how PAK1 activation controls brain development, and why specific chromatin remodeler components, e.g., BAF170 encoded by SMARCC2 in autism, await clarification.

The neurodevelopmental transcriptome of the Drosophila melanogaster microcephaly gene abnormal spindle reveals a role for temporal transcription factors and the immune system in regulating brain size

The coordination of cellular behaviors during neurodevelopment is critical for determining the form, function, and size of the central nervous system. Mutations in the vertebrate Abnormal Spindle-Like, Microcephaly Associated (ASPM) gene and its Drosophila melanogaster ortholog abnormal spindle (asp) lead to microcephaly, a reduction in overall brain size whose etiology remains poorly defined. Here we provide the neurodevelopmental transcriptional landscape for a Drosophila model for autosomal recessive primary microcephaly (MCPH) and extend our findings into the functional realm in an attempt to identify the key cellular mechanisms responsible for Asp-dependent brain growth and development. We identify multiple transcriptomic signatures, including new patterns of co-expressed genes in the developing CNS. Defects in optic lobe neurogenesis were detected in larval brains through downregulation of temporal transcription factors (tTFs) and Notch signaling targets, which correlated with a significant reduction in brain size and total cell numbers during the neurogenic window of development. We also found inflammation as a hallmark of asp MCPH brains, detectable throughout every stage of CNS development, which also contributes to the brain size phenotype. Finally, we show that apoptosis is not a primary driver of the asp MCPH phenotype, further highlighting an intrinsic Asp-dependent neurogenesis promotion mechanism that is independent of cell death. Collectively, our results suggest that the etiology of asp MCPH is complex and that a comprehensive view of the cellular basis of the disorder requires an understanding of how multiple pathway inputs collectively determine the microcephaly phenotype.

CLEC16A interacts with retromer and TRIM27, and its loss impairs endosomal trafficking and neurodevelopment

CLEC16A is a membrane-associated C-type lectin protein that functions as a E3-ubiquitin ligase. CLEC16A regulates autophagy and mitophagy, and reportedly localizes to late endosomes. GWAS studies have associated CLEC16A SNPs to various auto-immune and neurological disorders, including multiple sclerosis and Parkinson disease. Studies in mouse models imply a role for CLEC16A in neurodegeneration. We identified bi-allelic CLEC16A truncating variants in siblings from unrelated families presenting with a severe neurodevelopmental disorder including microcephaly, brain atrophy, corpus callosum dysgenesis, and growth retardation. To understand the function of CLEC16A in neurodevelopment we used in vitro models and zebrafish embryos. We observed CLEC16A localization to early endosomes in HEK293T cells. Mass spectrometry of human CLEC16A showed interaction with endosomal retromer complex subunits and the endosomal ubiquitin ligase TRIM27. Expression of the human variant leading to C-terminal truncated CLEC16A, abolishes both its endosomal localization and interaction with TRIM27, suggesting a loss-of-function effect. CLEC16A knockdown increased TRIM27 adhesion to early endosomes and abnormal accumulation of endosomal F-actin, a sign of disrupted vesicle sorting. Mutagenesis of clec16a by CRISPR-Cas9 in zebrafish embryos resulted in accumulated acidic/phagolysosome compartments, in neurons and microglia, and dysregulated mitophagy. The autophagocytic phenotype was rescued by wild-type human CLEC16A but not the C-terminal truncated CLEC16A. Our results demonstrate that CLEC16A closely interacts with retromer components and regulates endosomal fate by fine-tuning levels of TRIM27 and polymerized F-actin on the endosome surface. Dysregulation of CLEC16A-mediated endosomal sorting is associated with neurodegeneration, but it also causes accumulation of autophagosomes and unhealthy mitochondria during brain development.

Midbody Proteins Display Distinct Dynamics during Cytokinesis

The midbody is an organelle that forms between the two daughter cells during cytokinesis. It co-ordinates the abscission of the nascent daughter cells and is composed of a multitude of proteins that are meticulously arranged into distinct temporal and spatial localization patterns. However, very little is known about the mechanisms that regulate the localization and function of midbody proteins. Here, we analyzed the temporal and spatial profiles of key midbody proteins during mitotic exit under normal conditions and after treatment with drugs that affect phosphorylation and proteasome-mediated degradation to decipher the impacts of post-translational modifications on midbody protein dynamics. Our results highlighted that midbody proteins show distinct spatio-temporal dynamics during mitotic exit and cytokinesis that depend on both ubiquitin-mediated proteasome degradation and phosphorylation/de-phosphorylation. They also identified two discrete classes of midbody proteins: ‘transient’ midbody proteins—including Anillin, Aurora B and PRC1—which rapidly accumulate at the midbody after anaphase onset and then slowly disappear, and ‘stable’ midbody proteins—including CIT-K, KIF14 and KIF23—which instead persist at the midbody throughout cytokinesis and also post abscission. These two classes of midbody proteins display distinct interaction networks with ubiquitylation factors, which could potentially explain their different dynamics and stability during cytokinesis.

A Zebrafish/Drosophila Dual System Model for Investigating Human Microcephaly

Microcephaly presents in neurodevelopmental disorders with multiple aetiologies, including bi-allelic mutation in TUBGCP2, a component of the biologically fundamental and conserved microtubule-nucleation complex, γ-TuRC. Elucidating underlying principles driving microcephaly requires clear phenotype recapitulation and assay reproducibility, areas where go-to experimental models fall short. We present an alternative simple vertebrate/invertebrate dual system to investigate fundamental TUBGCP2-related processes driving human microcephaly and associated developmental traits. We show that antisense morpholino knockdown (KD) of the Danio rerio homolog, tubgcp2, recapitulates human TUBGCP2-associated microcephaly. Co-injection of wild type mRNA pre-empts microcephaly in 55% of KD zebrafish larvae, confirming causality. Body shortening observed in morphants is also rescued. Mitotic marker (pH3) staining further reveals aberrantly accumulated dividing brain cells in microcephalic tubgcp2 KD morphants, indicating that tubgcp2 depletion disrupts normal mitosis and/or proliferation in zebrafish neural progenitor brain cells. Drosophila melanogaster double knockouts (KO) for TUBGCP2 homologs Grip84/cg7716 also develop microcephalic brains with general microsomia. Exacerbated Grip84/cg7716-linked developmental aberration versus single mutations strongly suggests interactive or coinciding gene functions. We infer that tubgcp2 and Grip84/cg7716 affect brain size similarly to TUBGCP2 and recapitulate both microcephaly and microcephaly-associated developmental impact, validating the zebrafish/fly research model for human microcephaly. Given the conserved cross-phyla homolog function, the data also strongly support mitotic and/or proliferative disruption linked to aberrant microtubule nucleation in progenitor brain cells as key mechanistic defects for human microcephaly.

The Central Domain of MCPH1 Controls Development of the Cerebral Cortex and Gonads in Mice

MCPH1 is the first gene identified to be responsible for the human autosomal recessive disorder primary microcephaly (MCPH). Mutations in the N-terminal and central domains of MCPH1 are strongly associated with microcephaly in human patients. A recent study showed that the central domain of MCPH1, which is mainly encoded by exon 8, interacts with E3 ligase βTrCP2 and regulates the G2/M transition of the cell cycle. In order to investigate the biological functions of MCPH1’s central domain, we constructed a mouse model that lacked the central domain of MCPH1 by deleting its exon 8 (designated as Mcph1-Δe8). Mcph1-Δe8 mice exhibited a reduced brain size and thinner cortex, likely caused by a compromised self-renewal capacity and premature differentiation of Mcph1-Δe8 neuroprogenitors during corticogenesis. Furthermore, Mcph1-Δe8 mice were sterile because of a loss of germ cells in the testis and ovary. The embryonic fibroblasts of Mcph1-Δe8 mice exhibited premature chromosome condensation (PCC). All of these findings indicate that Mcph1-Δe8 mice are reminiscent of MCPH1 complete knockout mice and Mcph1-ΔBR1 mice. Our study demonstrates that the central domain of MCPH1 represses microcephaly, and is essential for gonad development in mammals.

Transmission ratio distortion of mutations in the master regulator of centriole biogenesis PLK4

The evolutionary conserved Polo-like kinase 4 (PLK4) is essential for centriole duplication, spindle assembly, and de novo centriole formation. In man, homozygous mutations in PLK4 lead to primary microcephaly, altered PLK4 expression is associated with aneuploidy in human embryos. Here, we report on a consanguineous four-generation family with 8 affected individuals compound heterozygous for a novel missense variant, c.881 T > G, and a deletion of the PLK4 gene. The clinical phenotype of the adult patients is mild compared to individuals with previously described PLK4 mutations. One individual was homozygous for the variant c.881G and phenotypically unaffected. The deletion was inherited by 14 of 16 offspring and thus exhibits transmission ratio distortion (TRD). Moreover, based on the already published families with PLK4 mutations, it could be shown that due to the preferential transmission of the mutant alleles, the number of affected offspring is significantly increased. It is assumed that reduced expression of PLK4 decreases the intrinsically high error rate of the first cell divisions after fertilization, increases the number of viable embryos and thus leads to preferential transmission of the deleted/mutated alleles.

Autosomal Recessive Primary Microcephaly: Not Just a Small Brain

Microcephaly or reduced head circumference results from a multitude of abnormal developmental processes affecting brain growth and/or leading to brain atrophy. Autosomal recessive primary microcephaly (MCPH) is the prototype of isolated primary (congenital) microcephaly, affecting predominantly the cerebral cortex. For MCPH, an accelerating number of mutated genes emerge annually, and they are involved in crucial steps of neurogenesis. In this review article, we provide a deeper look into the microcephalic MCPH brain. We explore cytoarchitecture focusing on the cerebral cortex and discuss diverse processes occurring at the level of neural progenitors, early generated and mature neurons, and glial cells. We aim to thereby give an overview of current knowledge in MCPH phenotype and normal brain growth.

Multifaceted Microcephaly-Related Gene MCPH1

MCPH1, or BRIT1, is often mutated in human primary microcephaly type 1, a neurodevelopmental disorder characterized by a smaller brain size at birth, due to its dysfunction in regulating the proliferation and self-renewal of neuroprogenitor cells. In the last 20 years or so, genetic and cellular studies have identified MCPH1 as a multifaceted protein in various cellular functions, including DNA damage signaling and repair, the regulation of chromosome condensation, cell-cycle progression, centrosome activity and the metabolism. Yet, genetic and animal model studies have revealed an unpredicted essential function of MPCH1 in gonad development and tumorigenesis, although the underlying mechanism remains elusive. These studies have begun to shed light on the role of MPCH1 in controlling various pathobiological processes of the disorder. Here, we summarize the biological functions of MCPH1, and lessons learnt from cellular and mouse models of MCPH1.

OUP accepted manuscript

Bloom syndrome (BS) is an autosomal recessive disease clinically characterized by primary microcephaly, growth deficiency, immunodeficiency and predisposition to cancer. It is mainly caused by biallelic loss-of-function mutations in the BLM gene, which encodes the BLM helicase, acting in DNA replication and repair processes. Here, we describe the gene expression profiles of three BS fibroblast cell lines harboring causative, biallelic truncating mutations obtained by single-cell (sc) transcriptome analysis. We compared the scRNA transcription profiles from three BS patient cell lines to two age-matched wild-type controls and observed specific deregulation of gene sets related to the molecular processes characteristically affected in BS, such as mitosis, chromosome segregation, cell cycle regulation and genomic instability. We also found specific upregulation of genes of the Fanconi anemia pathway, in particular FANCM, FANCD2 and FANCI, which encode known interaction partners of BLM. The significant deregulation of genes associated with inherited forms of primary microcephaly observed in our study might explain in part the molecular pathogenesis of microcephaly in BS, one of the main clinical characteristics in patients. Finally, our data provide first evidence of a novel link between BLM dysfunction and transcriptional changes in condensin complex I and II genes. Overall, our study provides novel insights into gene expression profiles in BS on an sc level, linking specific genes and pathways to BLM dysfunction.

Exome Sequencing Reveals Novel Variants and Expands the Genetic Landscape for Congenital Microcephaly

Congenital microcephaly causes smaller than average head circumference relative to age, sex and ethnicity and is most usually associated with a variety of neurodevelopmental disorders. The underlying etiology is highly heterogeneous and can be either environmental or genetic. Disruption of any one of multiple biological processes, such as those underlying neurogenesis, cell cycle and division, DNA repair or transcription regulation, can result in microcephaly. This etiological heterogeneity manifests in a clinical variability and presents a major diagnostic and therapeutic challenge, leaving an unacceptably large proportion of over half of microcephaly patients without molecular diagnosis. To elucidate the clinical and genetic landscapes of congenital microcephaly, we sequenced the exomes of 191 clinically diagnosed patients with microcephaly as one of the features. We established a molecular basis for microcephaly in 71 patients (37%), and detected novel variants in five high confidence candidate genes previously unassociated with this condition. We report a large number of patients with mutations in tubulin-related genes in our cohort as well as higher incidence of pathogenic mutations in MCPH genes. Our study expands the phenotypic and genetic landscape of microcephaly, facilitating differential clinical diagnoses for disorders associated with most commonly disrupted genes in our cohort.

Functional Genomics of PRUNE1 in Neurodevelopmental Disorders (NDDs) Tied to Medulloblastoma (MB) and Other Tumors

We analyze the fundamental functions of Prune_1 in brain pathophysiology. We discuss the importance and maintenance of the function of Prune_1 and how its perturbation influences both brain pathological conditions, neurodevelopmental disorder with microcephaly, hypotonia, and variable brain anomalies (NMIHBA; OMIM: 617481), and tumorigenesis of medulloblastoma (MB) with functional correlations to other tumors. A therapeutic view underlying recent discoveries identified small molecules and cell penetrating peptides to impair the interaction of Prune_1 with protein partners (e.g., Nm23-H1), thus further impairing intracellular and extracellular signaling (i.e., canonical Wnt and TGF-β pathways). Identifying the mechanism of action of Prune_1 as responsible for neurodevelopmental disorders (NDDs), we have recognized other genes which are found overexpressed in brain tumors (e.g., MB) with functional implications in neurodevelopmental processes, as mainly linked to changes in mitotic cell cycle processes. Thus, with Prune_1 being a significant target in NDDs, we discuss how its network of action can be dysregulated during brain development, thus generating cancer and metastatic dissemination.

p53 Activation in Genetic Disorders: Different Routes to the Same Destination

The tumor suppressor p53 is critical for preventing neoplastic transformation and tumor progression. Inappropriate activation of p53, however, has been observed in a number of human inherited disorders that most often affect development of the brain, craniofacial region, limb skeleton, and hematopoietic system. Genes related to these developmental disorders are essentially involved in transcriptional regulation/chromatin remodeling, rRNA metabolism, DNA damage-repair pathways, telomere maintenance, and centrosome biogenesis. Perturbation of these activities or cellular processes may result in p53 accumulation in cell cultures, animal models, and perhaps humans as well. Mouse models of several p53 activation-associated disorders essentially recapitulate human traits, and inactivation of p53 in these models can alleviate disorder-related phenotypes. In the present review, we focus on how dysfunction of the aforementioned biological processes causes developmental defects via excessive p53 activation. Notably, several disease-related genes exert a pleiotropic effect on those cellular processes, which may modulate the magnitude of p53 activation and establish or disrupt regulatory loops. Finally, we discuss potential therapeutic strategies for genetic disorders associated with p53 misactivation.