Mcph1/Brit1 deficiency promotes genomic instability and tumor formation in a mouse model

Loop Extrusion Machinery Impairments in Models and Disease

Structural maintenance of chromosomes (SMC) complexes play a crucial role in organizing the three-dimensional structure of chromatin, facilitating key processes such as gene regulation, DNA repair, and chromosome segregation. This review explores the molecular mechanisms and biological significance of SMC-mediated loop extrusion complexes, including cohesin, condensins, and SMC5/6, focusing on their structure, their dynamic function during the cell cycle, and their impact on chromatin architecture. We discuss the implications of impairments in loop extrusion machinery as observed in experimental models and human diseases. Mutations affecting these complexes are linked to various developmental disorders and cancer, highlighting their importance in genome stability and transcriptional regulation. Advances in model systems and genomic techniques have provided deeper insights into the pathological roles of SMC complex dysfunction, offering potential therapeutic avenues for associated diseases.

A telomere-related gene risk model for predicting prognosis and treatment response in acute myeloid leukemia

Acute myeloid leukemia (AML) is a prevalent hematological malignancy among adults. Recent studies suggest that the length of telomeres could significantly affect both the risk of developing AML and the overall survival (OS). Despite the limited focus on the prognostic value of telomere-related genes (TRGs) in AML, our study aims at addressing this gap by compiling a list of TRGs from TelNet, as well as collecting clinical information and TRGs expression data through the Gene Expression Omnibus (GEO) database. The GSE37642 dataset, sourced from GEO and based on the GPL96 platform, was divided into training and validation sets at a 6:4 ratio. Additionally, the GSE71014 dataset (based on the GPL10558 platform), GSE12417 dataset (based on the GPL96 and GPL570 platforms), and another portion of the GSE37642 dataset (based on the GPL570 platform) were designated as external testing sets. Univariate Cox regression analysis identified 96 TRGs significantly associated with OS. Subsequent Lasso-Cox stepwise regression analysis pinpointed eight TRGs (MCPH1, SLC25A6, STK19, PSAT1, KCTD15, DNMT3B, PSMD5, and TAF2) exhibiting robust predictive potential for patient survival. Both univariate and multivariate survival analyses unveiled TRG risk scores and age as independent prognostic variables. To refine the accuracy of survival prognosis, we developed both a nomogram integrating clinical parameters and a predictive risk score model based on TRGs. In subsequent investigations, associations were emphasized not solely regarding the TRG risk score and immune infiltration patterns but also concerning the response to immune-checkpoint inhibitor (ICI) therapy. In summary, the establishment of a telomere-associated genetic risk model offers a valuable tool for prognosticating AML outcomes, thereby facilitating informed treatment decisions.

The emerging role of MCPH1/BRIT1 in carcinogenesis

The MCPH1 gene, also known as BRCT-repeat inhibitor of hTERT expression (BRIT1), has three BRCA1 carboxyl-terminal domains which is an important regulator of DNA repair, cell cycle checkpoints and chromosome condensation. MCPH1/BRIT1 is also known as a tumour suppressor in different types of human cancer. The expression level of the MCPH1/BRIT1 gene is decreased at the DNA, RNA or protein level in a number of types of cancers including breast cancer, lung cancer, cervical cancer, prostate cancer and ovarian cancer compared to normal tissue. This review also showed that deregulation of MCPH1/BRIT1 is significantly associated with reduced overall survival in 57% (12/21) and relapsed free survival in 33% (7/21) of cancer types especially in oesophageal squamous cell carcinoma and renal clear cell carcinoma. A common finding of this study is that the loss of MCPH1/BRIT1 gene expression plays a key role in promoting genome instability and mutations supporting its function as a tumour suppressor gene.

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.

Bona Fide Tumor Suppressor Genes Hypermethylated in Melanoma: A Narrative Review

Loss-of-function events in tumor suppressor genes (TSGs) contribute to the development and progression of cutaneous malignant melanoma (CMM). Epigenetic alterations are the major mechanisms of TSG inactivation, in particular, silencing by promoter CpG-island hypermethylation. TSGs are valuable tools in diagnosis and prognosis and, possibly, in future targeted therapy. The aim of this narrative review is to outline bona fide TSGs affected by promoter CpG-island hypermethylation and their functional role in the progression of CMM. We conducted a systematic literature review to identify studies providing evidence of bona fide TSGs by cell line or animal experiments. We performed a broad first search and a gene-specific second search, supplemented by reference checking. We included studies describing bona fide TSGs in CMM with promoter CpG-island hypermethylation in which inactivating mechanisms were reported. We extracted data about protein role, pathway, experiments conducted to meet the bona fide criteria and hallmarks of cancer acquired by TSG inactivation. A total of 24 studies were included, describing 24 bona fide TSGs silenced by promoter CpG-island hypermethylation in CMM. Their effect on cell proliferation, apoptosis, growth, senescence, angiogenesis, migration, invasion or metastasis is also described. These data give further insight into the role of TSGs in the progression of CMM.

Microcephalin 1/BRIT1-TRF2 interaction promotes telomere replication and repair, linking telomere dysfunction to primary microcephaly

Telomeres protect chromosome ends from inappropriately activating the DNA damage and repair responses. Primary microcephaly is a key clinical feature of several human telomere disorder syndromes, but how microcephaly is linked to dysfunctional telomeres is not known. Here, we show that the microcephalin 1/BRCT-repeats inhibitor of hTERT (MCPH1/BRIT1) protein, mutated in primary microcephaly, specifically interacts with the TRFH domain of the telomere binding protein TRF2. The crystal structure of the MCPH1-TRF2 complex reveals that this interaction is mediated by the MCPH1 ₃₃₀YRLSP₃₃₄ motif. TRF2-dependent recruitment of MCPH1 promotes localization of DNA damage factors and homology directed repair of dysfunctional telomeres lacking POT1-TPP1. Additionally, MCPH1 is involved in the replication stress response, promoting telomere replication fork progression and restart of stalled telomere replication forks. Our work uncovers a previously unrecognized role for MCPH1 in promoting telomere replication, providing evidence that telomere replication defects may contribute to the onset of microcephaly.

Microcephaly family protein MCPH1 stabilizes RAD51 filaments

Microcephalin 1 (MCPH1) was identified from genetic mutations in patients with primary autosomal recessive microcephaly. In response to DNA double-strand breaks (DSBs), MCPH1 forms damage-induced foci and recruits BRCA2-RAD51 complex, a key component of the DSB repair machinery for homologous recombination (HR), to damage sites. Accordingly, the efficiency of HR is significantly attenuated upon depletion of MCPH1. The biochemical characteristics of MCPH1 and its functional interaction with the HR machinery had remained unclear due to lack of highly purified MCPH1 recombinant protein for functional study. Here, we established a mammalian expression system to express and purify MCPH1 protein. We show that MCPH1 is a bona fide DNA-binding protein and provide direct biochemical analysis of this MCPH family protein. Furthermore, we reveal that MCPH1 directly interacts with RAD51 at multiple contact points, providing evidence for how MCPH1 physically engages with the HR machinery. Importantly, we demonstrate that MCPH1 enhances the stability of RAD51 on single-strand DNA, a prerequisite step for RAD51-mediated recombination. Single-molecule tethered particle motion analysis showed a ∼2-fold increase in the lifetime of RAD51-ssDNA filaments in the presence of MCPH1. Thus, our study demonstrates direct crosstalk between microcephaly protein MCPH1 and the recombination component RAD51 for DSB repair.

Analysis of the "centrosome-ome" identifies MCPH1 deletion as a cause of centrosome amplification in human cancer

The centrosome is the microtubule organizing center of human cells and facilitates a myriad of cellular functions including organization of the mitotic spindle to ensure faithful chromosome segregation during mitosis, cell polarization and migration, and primary cilia formation. A numerical increase in centrosomes, or centrosome amplification (CA), is common in cancer and correlates with more aggressive clinical features and worse patient outcomes. However, the causes of CA in human cancer are unclear. Many previous studies have identified mechanisms of CA in cellulo, such as overexpression of PLK4, but it is unclear how often these are the primary mechanism in human disease. To identify a primary cause of CA, we analyzed The Cancer Genome Atlas (TCGA) genomic and transcriptomic data for genes encoding the 367 proteins that localize to the centrosome (the "centrosome-ome"). We identified the following candidates for primary causes of CA: gain-of-function alterations of CEP19, CEP72, CTNNB1, PTK2, NDRG1, SPATC1, TBCCD1; and loss-of-function alterations of CEP76, MCPH1, NEURL4, and NPM1. In cellulo analysis of these candidates revealed that loss of MCPH1/microcephalin caused the most robust increase in centriole number. MCPH1 deep gene deletions are seen in 5-15% of human cancers, depending on the anatomic site of the tumor. Mechanistic experiments demonstrated that loss of MCPH1 caused a CDK2-dependent increase in STIL levels at the centrosome to drive CA. We conclude that loss of MCPH1 is common in human cancer and is likely to be a cause of CA.

BRIT1 dysfunction confers synergistic inhibition of hepatocellular carcinoma by targeting poly (ADP-ribose) polymerases and PI3K

BRIT1 has emerged as a novel key player in homologous recombination (HR). It is located in 8p23, a locus frequently deleted in hepatocellular carcinoma (HCC). Previously, we found that BRIT1-deficiency triggered genomic instability and tumor formation in our mouse model. Here we aim to determine whether BRIT1 aberrations are implicated in HCC and, if so, whether they can be used for targeted therapy with PARP inhibitors and other agents. We analyzed HCC samples for BRIT1 alterations at DNA, RNA and protein levels. BRIT1 was found deleted and/or downregulated in ~30% of HCC samples; BRIT1 mutant K659fsX10 identified in HCC abolished DNA repair function. Notably, BRIT1 deletion was correlated with poor survival and high recurrence of HCC. To determine the role of BRIT1 deficiency in potentiating the drug response, we subsequently generated BRIT1-deficient HCC cells, determined their HR defects, and assessed their response to the PARPi olaparib and PI3K inhibitor in vitro and in mice. BRIT1-deficient HCC cells were HR defective and hypersensitive to olaparib alone or in combination with PI3K inhibitor BEZ235, both in vitro and in vivo. The cytotoxicity of olaparib alone or in combination with BEZ235 was largely alleviated by ectopic BRIT1. We also found that BEZ235 markedly enhanced the production of poly (ADP-ribose) and the level of double-strand breaks (DSB) and single-strand breaks (SSB) in BRIT1-deficient cells. In summary, our results identify BRIT1 deficiency as a potential driver for HCC development, and BRIT1 status is critical to sensitivity to treatment with olaparib and/or BEZ235. PI3K inhibition induces substantial DNA damage and makes cells more dependent on PARP activity in the context of BRIT1 deficiency, thus, BRIT1 depletion facilitates enhancing synthetic lethality of PARP inhibitors and PI3K inhibitors in HCC. This study provides a new mechanistic foundation for significantly expanding the application of PARPi in HCC therapy.

MCPH1 is essential for cellular adaptation to the G2-phase decatenation checkpoint

Cellular checkpoints controlling entry into mitosis monitor the integrity of the DNA and delay mitosis onset until the alteration is fully repaired. However, this canonical response can weaken, leading to a spontaneous bypass of the checkpoint, a process referred to as checkpoint adaptation. Here, we have investigated the contribution of microcephalin 1 (MCPH1), mutated in primary microcephaly, to the decatenation checkpoint, a less-understood G₂ pathway that delays entry into mitosis until chromosomes are properly disentangled. Our results demonstrate that, although MCPH1 function is dispensable for activation and maintenance of the decatenation checkpoint, it is required for the adaptive response that bypasses the topoisomerase II inhibition----mediated G₂ arrest. MCPH1, however, does not confer adaptation to the G₂ arrest triggered by the ataxia telangiectasia mutated- and ataxia telangiectasia and rad3 related-based DNA damage checkpoint. In addition to revealing a new role for MCPH1 in cell cycle control, our study provides new insights into the genetic requirements that allow cellular adaptation to G₂ checkpoints, a process that remains poorly understood.-Arroyo, M., Kuriyama, R., Guerrero, I., Keifenheim, D., Cañuelo, A., Calahorra, J., Sánchez, A., Clarke, D. J., Marchal, J. A. MCPH1 is essential for cellular adaptation to the G₂-phase decatenation checkpoint.

Tumor suppressor MCPH1 regulates gene expression profiles related to malignant conversion and chromosomal assembly

Strong inherited predisposition to breast cancer is estimated to cause about 5–10% of all breast cancer cases. As the known susceptibility genes, such as BRCA1 and BRCA2, explain only a fraction of this, additional predisposing genes and related biological mechanisms are actively being searched for. We have recently identified a recurrent MCPH1 germline mutation, p.Arg304ValfsTer3, as a breast cancer susceptibility allele. MCPH1 encodes a multifunctional protein involved in maintenance of genomic integrity and it is also somatically altered in various cancer types, including breast cancer. Additionally, biallelic MCPH1 mutations are causative for microcephaly and at cellular level premature chromosome condensation. To study the molecular mechanisms leading to cancer predisposition and malignant conversion, here we have modeled the effect of MCPH1 p.Arg304ValfsTer3 mutation using gene‐edited MCF10A breast epithelial cells. As a complementary approach, we also sought for additional potential cancer driver mutations in MCPH1 p.Arg304ValfsTer3 carrier breast tumors. We show that mutated MCPH1 de‐regulates transcriptional programs related to invasion and metastasis and leads to downregulation of histone genes. These global transcriptional changes are mirrored by significantly increased migration and invasion potential of the cells as well as abnormal chromosomal condensation both before and after mitosis. These findings provide novel molecular insights to MCPH1 tumor suppressor functions and establish a role in regulation of transcriptional programs related to malignant conversion and chromosomal assembly. The MCPH1 p.Arg304ValfsTer3 carrier breast tumors showed recurrent tumor suppressor gene TP53 mutations, which were also significantly over‐represented in breast tumors with somatically inactivated MCPH1.

What's new?

Even though several breast cancer susceptibility genes have been identified, additional molecular mechanisms behind predisposition and the promotion of malignant conversion remain obscure. Here, the authors show that a previously‐identified breast cancer predisposing allele in tumor suppressor MCPH1 deregulates transcriptional programs related to invasion and metastasis and leads to down‐regulation of histone genes. These global transcriptional changes are mirrored by increased cell migration and invasion potential and abnormal chromosomal condensation. The findings provide novel molecular insights into MCPH1 tumor suppressor functions and establish a role in the regulation of transcriptional programs related to malignant conversion and chromosomal assembly.

Silencing BRIT1 Facilitates the Abilities of Invasiveness and Migration in Trophoblast Cells

Background

The improper invasion of trophoblast cells (TC) can cause various diseases. BRCT-repeat inhibitor of hTERT expression (BRIT1) is involved in the invasion of tumors. Here, we analyzed the effects of BRIT1 on the invasion of TC.

Material/Methods

The expression of BRIT1 in JEG-3, B6Tert, and HTR8/SVneo cells was evaluated by transcription-quantitative polymerase chain reaction (RT-qPCR) and Western blotting. The viability, invasion, and migration of HTR8/SVneo cells were measured using cell counting kit-8 (CCK-8) and Transwell assays. The activities of pro-matrix metalloproteinase-2 (pro-MMP-2) and pro-MMP-9 were tested by gelatin zymography assay. The levels of invasion- and Wnt/β-catenin pathway-related factors were assessed by RT-qPCR and Western blotting.

Results

Levels of BRIT1 in HTR8/SVneo cells were higher than that of JEG-3 and B6Tert cells. The transfection efficiency of BRIT1 siRNA-2 was better than BRIT1 siRNA-1 in HTR8/SVneo cells. BRIT1 siRNA-2 did not change cell viability, whereas it promoted cell invasion and migration. BRIT1 siRNA-2 enhanced the activities of pro-MMP-2 and pro-MMP-9, as well MMP-2 and MMP-9 levels, and reduced tissue inhibitor of metalloproteinases-1 (TIMP-1) and TIMP-2 expression. Moreover, BRIT1 siRNA-2 significantly increased the levels of Wnt2, Wnt3, and β-catenin.

Conclusions

BRIT1 silencing accelerated the invasion and migration of TC and activated the Wnt/β-catenin pathway. Our results may provide new insights for finding new molecular targets to cure disease caused by insufficient invasion of TC.

Hybrid L1/2 + 2 method for gene selection in the Cox proportional hazards model

BACKGROUND AND OBJECTIVE

An important issue in genomic research is to identify the significant genes that related to survival from tens of thousands of genes. Although Cox proportional hazards model is a conventional survival analysis method, it does not induce the gene selection.

METHODS

In this paper, we extend the hybrid L_{1/2  + 2} regularization (HLR) idea to the censored survival situation, a new edition of sparse Cox model based on the HLR method has been proposed. We develop two algorithms for solving the HLR penalized Cox model; one is the coordinate descent algorithm with HLR thresholding operator, the other is the weight iteration method.

RESULTS

The proposed method was tested on six public mRNA data sets of serval kinds of cancers, AML, Breast cancer, Pancreatic cancer, DLBCL and Melanoma. The test results indicate that the method identified a small subset of genes but essential while giving best or equivalent predictive performance, as compared to some popular methods.

CONCLUSIONS

The results of empirical and simulations imply that the proposed strategy is highly competitive in studying high dimensional survival data among several state-of-the-art methods.

Altered mitochondrial and peroxisomal integrity in lipocalin-2-deficient mice with hepatic steatosis

Lipocalin-2 (LCN2) is a secreted adipokine that transports small hydrophobic molecules such as fatty acids and steroids. LCN2 limits bacterial growth by sequestering iron-containing siderophores and in mammalian liver protects against inflammation, infection, injury and other stressors. Because LCN2 modulates hepatic fat metabolism and homeostasis, we performed a comparative profiling of proteins and lipids of wild type (WT) and Lcn2-deficient mice fed either standard chow or a methionine- and choline-deficient (MCD) diet. Label-free proteomics and 2D-DIGE protein expression profiling revealed differential expression of BRIT1/MCPH1, FABP5, HMGB1, HBB2, and L-FABP, results confirmed by Western blotting. Gene ontology enrichment analysis identified enrichment for genes associated with mitochondrial membrane permeabilization and metabolic processes involving carboxylic acid. Measurements of mitochondrial membrane potential, mitochondrial chelatable iron pool, intracellular lipid peroxidation, and peroxisome numbers in primary hepatocytes confirmed that LCN2 regulates mitochondrial and peroxisomal integrity. Matrix-Assisted Laser Desorption/Ionization Time-Of-Flight (MALDI-TOF) mass spectrometry imaging identified significant changes to sphingomyelins, triglycerides, and glycerophospholipids in livers of mice fed an MCD diet regardless of LCN2 status. However, two arachidonic acid-containing glycerophospholipids were increased in Lcn2-deficient livers. Thus, LCN2 influences peroxisomal and mitochondrial biology in the liver to maintain triglyceride balance, handle oxidative stress, and control apoptosis.

BRCT-domain protein BRIT1 influences class switch recombination

DNA double-strand breaks (DSBs) serve as obligatory intermediates for Ig heavy chain (Igh) class switch recombination (CSR). The mechanisms by which DSBs are resolved to promote long-range DNA end-joining while suppressing genomic instability inherently associated with DSBs are yet to be fully elucidated. Here, we use a targeted short-hairpin RNA screen in a B-cell lymphoma line to identify the BRCT-domain protein BRIT1 as an effector of CSR. We show that conditional genetic deletion of BRIT1 in mice leads to a marked increase in unrepaired Igh breaks and a significant reduction in CSR in ex vivo activated splenic B cells. We find that the C-terminal tandem BRCT domains of BRIT1 facilitate its interaction with phosphorylated H2AX and that BRIT1 is recruited to the Igh locus in an activation-induced cytidine deaminase (AID) and H2AX-dependent fashion. Finally, we demonstrate that depletion of another BRCT-domain protein, MDC1, in BRIT1-deleted B cells increases the severity of CSR defect over what is observed upon loss of either protein alone. Our results identify BRIT1 as a factor in CSR and demonstrate that multiple BRCT-domain proteins contribute to optimal resolution of AID-induced DSBs.

The DNA damage response molecule MCPH1 in brain development and beyond

Microcephalin (MCPH1) is identified as being responsible for the neurodevelopmental disorder primary microcephaly type 1, which is characterized by a smaller-than-normal brain size and mental retardation. MCPH1 has originally been identified as an important regulator of telomere integrity and of cell cycle control. Genetic and cellular studies show that MCPH1 controls neurogenesis by coordinating the cell cycle and the centrosome cycle and thereby regulating the division mode of neuroprogenitors to prevent the exhaustion of the progenitor pool and thereby microcephaly. In addition to its role in neurogenesis, MCPH1 plays a role in gonad development. MCPH1 also functions as a tumor suppressor in several human cancers as well as in mouse models. Here, we review the role of MCPH1 in DNA damage response, cell cycle control, chromosome condensation and chromatin remodeling. We also summarize the studies on the biological functions of MCPH1 in brain size determination and in pathologies, including infertility and cancer.

Targeted Next-Generation Sequencing Identifies a Recurrent Mutation in MCPH1 Associating with Hereditary Breast Cancer Susceptibility

Breast cancer is strongly influenced by hereditary risk factors, a majority of which still remain unknown. Here, we performed a targeted next-generation sequencing of 796 genes implicated in DNA repair in 189 Finnish breast cancer cases with indication of hereditary disease susceptibility and focused the analysis on protein truncating mutations. A recurrent heterozygous mutation (c.904_916del, p.Arg304ValfsTer3) was identified in early DNA damage response gene, MCPH1, significantly associating with breast cancer susceptibility both in familial (5/145, 3.4%, P = 0.003, OR 8.3) and unselected cases (16/1150, 1.4%, P = 0.016, OR 3.3). A total of 21 mutation positive families were identified, of which one-third exhibited also brain tumors and/or sarcomas (P = 0.0007). Mutation carriers exhibited significant increase in genomic instability assessed by cytogenetic analysis for spontaneous chromosomal rearrangements in peripheral blood lymphocytes (P = 0.0007), suggesting an effect for MCPH1 haploinsufficiency on cancer susceptibility. Furthermore, 40% of the mutation carrier tumors exhibited loss of the wild-type allele. These findings collectively provide strong evidence for MCHP1 being a novel breast cancer susceptibility gene, which warrants further investigations in other populations.

Chromosome structure deficiencies in MCPH1 syndrome

Mutations in the MCPH1 gene result in primary microcephaly in combination with a unique cellular phenotype of defective chromosome condensation. MCPH1 patient cells display premature chromosome condensation in G2 phase of the cell cycle and delayed decondensation in early G1 phase, observable as an increased proportion of cells with prophase-like appearance. MCPH1 deficiency thus appears to uncouple the chromosome cycle from the coordinated series of events that take place during mitosis such as some phases of the centrosome cycle and nuclear envelope breakdown. Here, we provide a further characterization of the effects of MCPH1 loss-of-function on chromosome morphology. In comparison to healthy controls, chromosomes of MCPH1 patients are shorter and display a pronounced coiling of their central chromatid axes. In addition, a substantial fraction of metaphase chromosomes shows apparently unresolved chromatids with twisted appearance. The patient chromosomes also showed signs of defective centromeric cohesion, which become more apparent and pronounced after harsh hypotonic conditions. Taking together, the observed alterations indicate additional so far unknown functions of MCPH1 during chromosome shaping and dynamics.

MCPH1: a window into brain development and evolution

The development of the mammalian cerebral cortex involves a series of mechanisms: from patterning, progenitor cell proliferation and differentiation, to neuronal migration. Many factors influence the development of the cerebral cortex to its normal size and neuronal composition. Of these, the mechanisms that influence the proliferation and differentiation of neural progenitor cells are of particular interest, as they may have the greatest consequence on brain size, not only during development but also in evolution. In this context, causative genes of human autosomal recessive primary microcephaly, such as ASPM and MCPH1, are attractive candidates, as many of them show positive selection during primate evolution. MCPH1 causes microcephaly in mice and humans and is involved in a diverse array of molecular functions beyond brain development, including DNA repair and chromosome condensation. Positive selection of MCPH1 in the primate lineage has led to much insight and discussion of its role in brain size evolution. In this review, we will present an overview of MCPH1 from these multiple angles, and whilst its specific role in brain size regulation during development and evolution remain elusive, the pieces of the puzzle will be discussed with the aim of putting together the full picture of this fascinating gene.