Modeling Human Primary Microcephaly With hiPSC-Derived Brain Organoids Carrying CPAP-E1235V Disease-Associated Mutant Protein

Meiotic divisions and round spermatid formation do not require centriole duplication in mice

Centrosomes, composed of centrioles and pericentriolar matrix proteins, are traditionally viewed as essential microtubule-organizing centers (MTOCs) that facilitate bipolar spindle formation and chromosome segregation during spermatogenesis. In this study, we investigated the role of centrioles in male germ cell development by using a murine conditional knockout (cKO) of Sas4, a critical component of centriole biogenesis. We found that while centriole duplication was impaired in Sas4 cKO spermatocytes, these cells were still capable of progressing through meiosis I and II. Chromosome segregation was able to proceed through the formation of a non-centrosomal MTOC, indicating that centrioles are not required for meiotic divisions. However, spermatids that inherited fewer than two centrioles exhibited severe defects in spermiogenesis, including improper manchette formation, constricted perinuclear rings, disrupted acrosome morphology, and failure to form flagella. Consequently, Sas4 cKO males were infertile due to the absence of functional spermatozoa. Our findings demonstrate that while centrioles are dispensable for meiosis in male germ cells, they are essential for spermiogenesis and sperm maturation. This work provides key insights into the role of centrosomes in male fertility and may have implications for understanding certain conditions of male infertility associated with centriole defects.

Biomedical applications of organoids in genetic diseases

Organoid technology has significantly transformed biomedical research by providing exceptional prospects for modeling human tissues and disorders in a laboratory setting. It has significant potential for understanding the intricate relationship between genetic mutations, cellular phenotypes, and disease pathology, especially in the field of genetic diseases. The intersection of organoid technology and genetic research offers great promise for comprehending the pathophysiology of genetic diseases and creating innovative treatment approaches customized for specific patients. This review aimed to present a thorough analysis of the current advancements in organoid technology and its biomedical applications for genetic diseases. We examined techniques for modeling genetic disorders using organoid platforms, analyze the approaches for incorporating genetic disease organoids into clinical practice, and showcase current breakthroughs in preclinical application, individualized healthcare, and transplantation. Through the integration of knowledge from several disciplines, such as genetics, regenerative medicine, and biological engineering, our aim is to enhance our comprehension of the complex connection between genetic variations and organoid models in relation to human health and disease.

Using cortical organoids to understand the pathogenesis of malformations of cortical development

Malformations of cortical development encompass a broad range of disorders associated with abnormalities in corticogenesis. Widespread abnormalities in neuronal formation or migration can lead to small head size or microcephaly with disorganized placement of cell types. Specific, localized malformations are termed focal cortical dysplasias (FCD). Neurodevelopmental disorders are common in all types of malformations of cortical development with the most prominent being refractory epilepsy, behavioral disorders such as autism spectrum disorder (ASD), and learning disorders. Several genetic pathways have been associated with these disorders from control of cell cycle and cytoskeletal dynamics in global malformations to variants in growth factor signaling pathways, especially those interacting with the mechanistic target of rapamycin (mTOR), in FCDs. Despite advances in understanding these disorders, the underlying developmental pathways that lead to lesion formation and mechanisms through which defects in cortical development cause specific neurological symptoms often remains unclear. One limitation is the difficulty in modeling these disorders, as animal models frequently do not faithfully mirror the human phenotype. To circumvent this obstacle, many investigators have turned to three-dimensional human stem cell models of the brain, known as organoids, because they recapitulate early neurodevelopmental processes. High throughput analysis of these organoids presents a promising opportunity to model pathophysiological processes across the breadth of malformations of cortical development. In this review, we highlight advances in understanding the pathophysiology of brain malformations using organoid models.

The power of human stem cell-based systems in the study of neurodevelopmental disorders

Neurodevelopmental disorders (NDDs) affect 15% of children and are usually associated with intellectual disability, seizures, and autistic behaviors, among other neurological presentations. Mutations in a wide spectrum of gene families alter key stages of human brain development, leading to defects in neural circuits or brain architecture. Studies in animal systems have provided important insights into the pathobiology of several NDDs. Human stem cell technologies provide a complementary system that allows functional manipulation of human brain cells during developmental stages that would otherwise be inaccessible during human fetal brain development. Therefore, stem cell-based models advance our understanding of human brain development by revealing human-specific mechanisms contributing to the broad pathogenesis of NDDs. We provide a comprehensive overview of the latest research on two and three-dimensional human stem cell-based models. First, we discuss convergent cellular and molecular phenotypes across different NDDs that have been revealed by human iPSC systems. Next, we examine the contribution of in vitro human neural systems to the development of promising therapeutic strategies. Finally, we explore the potential of stem cell systems to draw mechanistic insight for the study of sex dimorphism within NDDs.

Regulation of p53 by the mitotic surveillance/stopwatch pathway: implications in neurodevelopment and cancer

The transcription factor p53 (encoded by TP53) plays diverse roles in human development and disease. While best known for its role in tumor suppression, p53 signaling also influences mammalian development by triggering cell fate decisions in response to a wide variety of stresses. After over 4 decades of study, a new pathway that triggers p53 activation in response to mitotic delays was recently identified. Termed the mitotic surveillance or mitotic stopwatch pathway, the USP28 and 53BP1 proteins activate p53 in response to delayed mitotic progression to control cell fate and promote genomic stability. In this Minireview, I discuss its identification, potential roles in neurodevelopmental disorders and cancer, as well as explore outstanding questions about its function, regulation and potential use as a biomarker for anti-mitotic therapies.

iTRAQ-Based Serum Proteomic Analysis Reveals Multifactorial Cellular Function Impairment and Aggravated Systematic Inflammation in Drug-free Obsessive-Compulsive Disorders

Obsessive-compulsive disorder (OCD) is a debilitating mental disorder with obvious difficulties in treatment. Its pathogenesis has not been fully elucidated. Further understanding of etiology and mechanism needs to be explored further. We employed the isobaric tag for relative and absolute quantitation (iTRAQ)-based proteomic analysis to compare serum proteome profile between OCD patients and healthy controls, in order to find out the possible mechanism of OCD in the downstream biological process. Eighty-one drug-free OCD patients and 78 healthy controls were enrolled. A total of 475 proteins were identified. Totally, 80 proteins with p < 0.05 were selected for gene set enrichment analysis (GSEA), and only those with a fold change ≥1.2 and q value <0.2 between groups were accepted as differentially expressed proteins (DEPs). We observed a significant enrichment of immuno-inflammation-related pathways, along with intriguing expression trends that immuno-inflammation-related proteins were upregulated in GSEA. After that, 2 up-regulated proteins and 13 down-regulated ones were accepted as DEP. According to the available literature, most of the DEPs have not been reported in OCD. These DEPs were enriched in 121 gene ontology (GO) terms, including hepatocyte growth factor receptor activity, angiogenin-PRI complex, and so on. DEPs were enriched in pathways including adherens junction in the Kyoto Encyclopedia of Genes and Genomes (KEGG) database. Alterations in DEPs including STXBP5L, GRN, and ANG were validated in OCD animal models. Our study suggested that OCD patients manifested multifactorial impairment in neuronal or non-neuronal cellular function under the inflammatory background. Further research employing larger sample sizes, longitudinal design, stratified analysis, and multiomics methodology will be needed. Experiments in laboratories were essential in illuminating the mechanism.

Entosis implicates a new role for P53 in microcephaly pathogenesis, beyond apoptosis

Entosis, a form of cell cannibalism, is a newly discovered pathogenic mechanism leading to the development of small brains, termed microcephaly, in which P53 activation was found to play a major role. Microcephaly with entosis, found in Pals1 mutant mice, displays P53 activation that promotes entosis and apoptotic cell death. This previously unappreciated pathogenic mechanism represents a novel cellular dynamic in dividing cortical progenitors which is responsible for cell loss. To date, various recent models of microcephaly have bolstered the importance of P53 activation in cell death leading to microcephaly. P53 activation caused by mitotic delay or DNA damage manifests apoptotic cell death which can be suppressed by P53 removal in these animal models. Such genetic studies attest P53 activation as quality control meant to eliminate genomically unfit cells with minimal involvement in the actual function of microcephaly associated genes. In this review, we summarize the known role of P53 activation in a variety of microcephaly models and introduce a novel mechanism wherein entotic cell cannibalism in neural progenitors is triggered by P53 activation.

Emerging principles of primary cilia dynamics in controlling tissue organization and function

Primary cilia project from the surface of most vertebrate cells and are key in sensing extracellular signals and locally transducing this information into a cellular response. Recent findings show that primary cilia are not merely static organelles with a distinct lipid and protein composition. Instead, the function of primary cilia relies on the dynamic composition of molecules within the cilium, the context-dependent sensing and processing of extracellular stimuli, and cycles of assembly and disassembly in a cell- and tissue-specific manner. Thereby, primary cilia dynamically integrate different cellular inputs and control cell fate and function during tissue development. Here, we review the recently emerging concept of primary cilia dynamics in tissue development, organization, remodeling, and function.

Separation-of-function MCPH-associated mutations in CPAP affect centriole number and length

Centrioles are microtubule-based cylindrical ultrastructures characterized by their definite size and robustness. The molecular capping protein, CPAP (also known as CENPJ) engages its N-terminal region with the centriole microtubules to regulate their length. Nevertheless, the conserved C-terminal glycine-rich G-box of CPAP, which interacts with the centriole inner cartwheel protein STIL, is frequently mutated in primary microcephaly (MCPH) patients. Here, we show that two different MCPH-associated variants, E1235V and D1196N in the CPAP G-box, affect distinct functions at centrioles. The E1235V mutation reduces CPAP centriole recruitment and causes overly long centrioles. The D1196N mutation increases centriole numbers without affecting centriole localization. Both mutations prevent binding to STIL, which controls centriole duplication. Our work highlights the involvement of an alternative CEP152-dependent route for CPAP centriole localization. Molecular dynamics simulations suggest that E1235V leads to an increase in G-box flexibility, which could have implications on its molecular interactions. Collectively, we demonstrate that a CPAP region outside the microtubule-interacting domains influences centriole number and length, which translates to spindle defects and reduced cell viability. Our work provides new insights into the molecular causes of primary microcephaly.

The impact of TP53 activation and apoptosis in primary hereditary microcephaly

Autosomal recessive primary microcephaly (MCPH) is a constellation of disorders that share significant brain size reduction and mild to moderate intellectual disability, which may be accompanied by a large variety of more invalidating clinical signs. Extensive neural progenitor cells (NPC) proliferation and differentiation are essential to determine brain final size. Accordingly, the 30 MCPH loci mapped so far (MCPH1-MCPH30) encode for proteins involved in microtubule and spindle organization, centriole biogenesis, nuclear envelope, DNA replication and repair, underscoring that a wide variety of cellular processes is required for sustaining NPC expansion during development. Current models propose that altered balance between symmetric and asymmetric division, as well as premature differentiation, are the main mechanisms leading to MCPH. Although studies of cellular alterations in microcephaly models have constantly shown the co-existence of high DNA damage and apoptosis levels, these mechanisms are less considered as primary factors. In this review we highlight how the molecular and cellular events produced by mutation of the majority of MCPH genes may converge on apoptotic death of NPCs and neurons, via TP53 activation. We propose that these mechanisms should be more carefully considered in the alterations of the sophisticated equilibrium between proliferation, differentiation and death produced by MCPH gene mutations. In consideration of the potential druggability of cell apoptotic pathways, a better understanding of their role in MCPH may significantly facilitate the development of translational approaches.

Research models of neurodevelopmental disorders: The right model in the right place

Neurodevelopmental disorders (NDDs) are a heterogeneous group of impairments that affect the development of the central nervous system leading to abnormal brain function. NDDs affect a great percentage of the population worldwide, imposing a high societal and economic burden and thus, interest in this field has widely grown in recent years. Nevertheless, the complexity of human brain development and function as well as the limitations regarding human tissue usage make their modeling challenging. Animal models play a central role in the investigation of the implicated molecular and cellular mechanisms, however many of them display key differences regarding human phenotype and in many cases, they partially or completely fail to recapitulate them. Although in vitro two-dimensional (2D) human-specific models have been highly used to address some of these limitations, they lack crucial features such as complexity and heterogeneity. In this review, we will discuss the advantages, limitations and future applications of in vivo and in vitro models that are used today to model NDDs. Additionally, we will describe the recent development of 3-dimensional brain (3D) organoids which offer a promising approach as human-specific in vitro models to decipher these complex disorders.

Advantages of CRISPR-Cas9 combined organoid model in the study of congenital nervous system malformations

In the past 10 years, gene-editing and organoid culture have completely changed the process of biology. Congenital nervous system malformations are difficult to study due to their polygenic pathogenicity, the complexity of cellular and neural regions of the brain, and the dysregulation of specific neurodevelopmental processes in humans. Therefore, the combined application of CRISPR-Cas9 in organoid models may provide a technical platform for studying organ development and congenital diseases. Here, we first summarize the occurrence of congenital neurological malformations and discuss the different modeling methods of congenital nervous system malformations. After that, it focuses on using organoid to model congenital nervous system malformations. Then we summarized the application of CRISPR-Cas9 in the organoid platform to study the pathogenesis and treatment strategies of congenital nervous system malformations and finally looked forward to the future.

Using mammary organoids to study cilia

Cilia are hair-like projections that assemble at the surface of cells in various tissues of multicellular organisms through a complex cell biological process called ciliogenesis. Cilia can assemble as single structures per cell (i.e. non-motile primary cilia), which act as cell signaling centers that dictate cell fate, or can be assembled in distinct cell types as many copies per cell (i.e. motile cilia) that beat to move fluids at the cell surface. The mechanisms that orchestrate formation and function of cilia, which are dysregulated in pathological settings such as ciliopathies, remain incompletely understood. Stem cell-derived organoids represent valuable models to study the mechanisms of ciliogenesis, ciliary signaling, and ciliary beating that collectively promote tissue development and homeostasis. Here, we present a comprehensive protocol for the growth of mammary organoids derived from mouse mammary stem cells and for immunofluorescence staining of primary cilia in these three-dimensional structures.