Nedd1 expression as a marker of dynamic centrosomal localization during mouse embryonic development

Genome-wide DNA methylation profiles may reveal new possible epigenetic pathogenesis of sporadic congenital cataract

Aim: To investigate the possible epigenetic pathogenesis of sporadic congenital cataract. Materials & methods: We conducted whole genome bisulfite sequencing on peripheral blood from sporadic binocular or monocular congenital cataract patients and cataract-free participants. Results: We found massive differentially methylated regions within the whole genomes between any two groups. Meanwhile, we identified five genes (ACTN4, ACTG1, TUBA1A, TUBA1C, TUBB4B) for the binocular and control groups and TUBA1A for the monocular and control groups as the core differentially methylated region-related genes. The proteins encoded by these core genes are involved in building cytoskeleton and intercellular junctions. Conclusion: Changes in the methylation levels of core genes may disturb the function of cytoskeleton and intercellular junctions, eventually leading to sporadic congenital cataract.

Plk4 and Aurora A cooperate in the initiation of acentriolar spindle assembly in mammalian oocytes

Establishing the bipolar spindle in mammalian oocytes after their prolonged arrest is crucial for meiotic fidelity and subsequent development. In contrast to somatic cells, the first meiotic spindle assembles in the absence of centriole-containing centrosomes. Ran-GTP can promote microtubule nucleation near chromatin, but additional unidentified factors are postulated for the activity of multiple acentriolar microtubule organizing centers in the oocyte. We now demonstrate that partially overlapping, nonredundant functions of Aurora A and Plk4 kinases contribute to initiate acentriolar meiosis I spindle formation. Loss of microtubule nucleation after simultaneous chemical inhibition of both kinases can be significantly rescued by drug-resistant Aurora A alone. Drug-resistant Plk4 can enhance Aurora A-mediated rescue, and, accordingly, Plk4 can phosphorylate and potentiate the activity of Aurora A in vitro. Both kinases function distinctly from Ran, which amplifies microtubule growth. We conclude that Aurora A and Plk4 are rate-limiting factors contributing to microtubule growth as the acentriolar oocyte resumes meiosis.

Ulk4 Is Essential for Ciliogenesis and CSF Flow

Ciliopathies are an emerging class of devastating disorders with pleiotropic symptoms affecting both the central and peripheral systems and commonly associated with hydrocephalus. Even though ciliary components and three master transcriptional regulators have been identified, little is known about the signaling molecules involved. We previously identified a novel gene, Unc51-like-kinase 4 (ULK4), as a risk factor of neurodevelopmental disorders. Here we took multidisciplinary approaches and uncovered essential roles of Ulk4 in ciliogenesis. We show that Ulk4 is predominantly expressed in the ventricular system, and Ulk4(tm1a/tm1a) ependymal cells display reduced/disorganized cilia with abnormal axonemes. Ulk4(tm1a/tm1a) mice exhibit dysfunctional subcommissural organs, obstructive aqueducts, and impaired CSF flow. Mechanistically, we performed whole-genome RNA sequencing and discovered that Ulk4 regulates the Foxj1 pathway specifically and an array of other ciliogenesis molecules. This is the first evidence demonstrating that ULK4 plays a vital role in ciliogenesis and that deficiency of ULK4 can cause hydrocephalus and ciliopathy-related disorders.

SIGNIFICANCE STATEMENT

Ciliopathies are an emerging class of devastating disorders with pleiotropic symptoms affecting both the central and peripheral systems. Ciliopathies are commonly associated with hydrocephalus, and Unc51-like-kinase 4 (Ulk4) has been identified as one of 12 genes causing hydrocephalus in mutants. Here we uncover an essential role of Ulk4 in ciliogenesis. Ulk4 is predominantly expressed in the ventricles, and mutant ependymal cells display reduced/disorganized/nonfunctional motile cilia with abnormal axonemes and impaired CSF flow. Ulk4 modulates expression of the master regulator of ciliogenesis, Foxj1, and other ciliogenesis molecules. This is the first report demonstrating a vital role of Ulk4 in ciliogenesis. ULK4 deficiency may be implicated in human hydrocephalus and other ciliopathy-related disorders.

Loss of CDK5RAP2 affects neural but not non-neural mESC differentiation into cardiomyocytes

Biallelic mutations in the gene encoding centrosomal CDK5RAP2 lead to autosomal recessive primary microcephaly (MCPH), a disorder characterized by pronounced reduction in volume of otherwise architectonical normal brains and intellectual deficit. The current model for the microcephaly phenotype in MCPH invokes a premature shift from symmetric to asymmetric neural progenitor-cell divisions with a subsequent depletion of the progenitor pool. The isolated neural phenotype, despite the ubiquitous expression of CDK5RAP2, and reports of progressive microcephaly in individual MCPH cases prompted us to investigate neural and non-neural differentiation of Cdk5rap2-depleted and control murine embryonic stem cells (mESC). We demonstrate an accumulating proliferation defect of neurally differentiating Cdk5rap2-depleted mESC and cell death of proliferative and early postmitotic cells. A similar effect does not occur in non-neural differentiation into beating cardiomyocytes, which is in line with the lack of non-central nervous system features in MCPH patients. Our data suggest that MCPH is not only caused by premature differentiation of progenitors, but also by reduced propagation and survival of neural progenitors.

The molecular mechanisms underlying lens fiber elongation

Lens fiber cells are highly elongated cells with complex membrane morphologies that are critical for the transparency of the ocular lens. Investigations into the molecular mechanisms underlying lens fiber cell elongation were first reported in the 1960s, however, our understanding of the process is still poor nearly 50 years later. This review summarizes what is currently hypothesized about the regulation of lens fiber cell elongation along with the available experimental evidence, and how this information relates to what is known about the regulation of cell shape/elongation in other cell types, particularly neurons.

Loss of γ-tubulin, GCP-WD/NEDD1 and CDK5RAP2 from the Centrosome of Neurons in Developing Mouse Cerebral and Cerebellar Cortex

It has been recently reported that the centrosome of neurons does not have microtubule nucleating activity. Microtubule nucleation requires γ-tubulin as well as its recruiting proteins, GCP-WD/NEDD1 and CDK5RAP2 that anchor γ-tubulin to the centrosome. Change in the localization of these proteins during in vivo development of brain, however, has not been well examined. In this study we investigate the localization of γ-tubulin, GCP-WD and CDK5RAP2 in developing cerebral and cerebellar cortex with immunofluorescence. We found that γ-tubulin and its recruiting proteins were localized at centrosomes of immature neurons, while they were lost at centrosomes in mature neurons. This indicated that the loss of microtubule nucleating activity at the centrosome of neurons is due to the loss of γ-tubulin-recruiting proteins from the centrosome. RT-PCR analysis revealed that these proteins are still expressed after birth, suggesting that they have a role in microtubule generation in cell body and dendrites of mature neurons. Microtubule regrowth experiments on cultured mature neurons showed that microtubules are nucleated not at the centrosome but within dendrites. These data indicated the translocation of microtubule-organizing activity from the centrosome to dendrites during maturation of neurons, which would explain the mixed polarity of microtubules in dendrites.

Developmental role of plk4 in Xenopus laevis and Danio rerio: implications for Seckel Syndrome

The polo-like kinases are a family of conserved serine/threonine kinases that play multiple roles in regulation of the cell cycle. Unlike its four other family members, the role of Plk4 in embryonic development has not been well characterized. In mice, Plk4(-)(/)(-) embryos arrest at E7.5, just prior to the initiation of somitogenesis. This has led to the hypothesis that Plk4 expression may be essential to somitogenesis. Recently characterized human mutations lead to Seckel Syndrome. Riboprobe in situ hybridization revealed that plk4 is ubiquitously expressed during early stages of development of Xenopus and Danio; in later stages, expression in frogs restricts to somites as well as eye, otic vesicle, and branchial arch, and brain. Expression patterns in fish remain ubiquitous. Both somite and eye development require planar cell polarity, and disruption of plk4 function in frog by means of morpholino-mediated translational knockdown yields orientational disorganization of both these structures. These results provide the first steps in defining a new role for plk4 in organogenesis and implies a role in planar cell polarity, segmentation, and in recently described PLK4 mutations in human.

Murine macrophages response to iron

Macrophages play a critical role at the crossroad between iron metabolism and immunity, being able to store and recycle iron derived from the phagocytosis of senescent erythrocytes. The way by which macrophages manage non-heme iron at physiological concentration is still not fully understood. We investigated protein changes in mouse bone marrow macrophages incubated with ferric ammonium citrate (FAC 10 μM iron). Differentially expressed spots were identified by nano RP-HPLC-ESI-MS/MS. Transcriptomic, metabolomics and western immunoblotting analyses complemented the proteomic approach. Pattern analysis was also used for identifying networks of proteins involved in iron homeostasis. FAC treatment resulted in higher abundance of several proteins including ferritins, cytoskeleton related proteins, glyceraldehyde-3-phosphate dehydrogenase (GAPDH) at the membrane level, vimentin, arginase, galectin-3 and macrophage migration inhibitory factor (MIF). Interestingly, GAPDH has been recently proposed to act as an alternative transferrin receptor for iron acquisition through internalization of the GAPDH-transferrin complex into the early endosomes. FAC treatment also induced the up-regulation of oxidative stress-related proteins (PRDX), which was further confirmed at the metabolic level (increase in GSSG, 8-isoprostane and pentose phosphate pathway intermediates) through mass spectrometry-based targeted metabolomics approaches. This study represents an example of the potential usefulness of "integarated omics" in the field of iron biology, especially for the elucidation of the molecular mechanisms controlling iron homeostasis in normal and disease conditions. This article is part of a Special Issue entitled: Integrated omics.

A potential role for NEDD1 and the centrosome in senescence of mouse embryonic fibroblasts

Mouse embryonic fibroblasts (MEFs) are commonly grown in cell culture and are known to enter senescence after a low number of passages as a result of oxidative stress. Oxidative stress has also been suggested to promote centrosome disruption; however, the contribution of this organelle to senescence is poorly understood. Therefore, this study aimed to assess the role of the centrosome in oxidative stress induced-senescence using MEFs as a model. We demonstrate here that coincident with the entry of late-passage MEFs into senescence, there was an increase in supernumerary centrosomes, most likely due to centrosome fragmentation. In addition, disrupting the centrosome in early-passage MEFs by depletion of neural precursor cell expressed developmentally downregulated gene 1 (NEDD1) also resulted in centrosomal fragmentation and subsequent premature entry into senescence. These data show that a loss of centrosomal integrity may contribute to the entry of MEFs into senescence in culture, and that centrosomal disruption can cause senescence.

A direct interaction with NEDD1 regulates gamma-tubulin recruitment to the centrosome

The centrosome is the primary microtubule organizing centre of the cell. γ-tubulin is a core component of the centrosome and is required for microtubule nucleation and centrosome function. The recruitment of γ-tubulin to centrosomes is mediated by its interaction with NEDD1, a WD40-repeat containing protein. Here we demonstrate that NEDD1 is likely to be oligomeric in vivo and binds directly to γ-tubulin through a small region of just 62 residues at the carboxyl-terminus of the protein. This carboxyl-terminal domain that binds γ-tubulin has a helical structure and is a stable tetramer in solution. Mutation of residues in NEDD1 that disrupt binding to γ-tubulin result in a mis-localization of γ-tubulin away from the centrosome. Hence, this study defines the binding site on NEDD1 that is required for its interaction with γ-tubulin, and shows that this interaction is required for the correct localization of γ-tubulin.

An essential function for the centrosomal protein NEDD1 in zebrafish development

The centrosome is the primary microtubule organising centre of the cell. It is composed of many proteins, some of which make up the core of the centrosome, whereas others are used for specific functions. Although the cellular roles of many centrosomal proteins are well defined, much less is known about their functions and the role of the centrosome in development. In this study we investigated the function of NEDD1, a critical component of the centrosome essential for microtubule nucleation, in zebrafish (Danio rerio) development. The zebrafish homologue of NEDD1 (zNEDD1) was cloned and found to have a similar localisation and function to mammalian NEDD1. We show that zNEDD1 is essential for survival, as a high level of knockdown was embryonic lethal. Partial knockdown of zNEDD1 caused abnormalities including an increase in mitotic and apoptotic cells. Pronounced phenotypic defects were seen in the brain, with a lack of defined brain structures, incomplete neural tube formation and a disorganisation of neurons. In addition, we show that a reduction in zNEDD1 resulted in the loss of gamma-tubulin at the centrosome. Our data thus demonstrate that zNEDD1 is critical for the recruitment of gamma-tubulin to the centrosome, and is essential for the proper development of zebrafish.

NEDD1 is crucial for meiotic spindle stability and accurate chromosome segregation in mammalian oocytes

Defects in meiotic spindle structure contribute to chromosome segregation errors leading to genomic instability in oocytes and embryos upon fertilization. In this study, we analyzed the mechanisms that control spindle microtubule nucleation and stability in mammalian oocytes, and identified NEDD1/GCP-WD as a key regulator. NEDD1 specifically co-localizes with gamma-tubulin and pericentrin at microtubule-organizing centers (MTOCs) in mouse oocytes arrested at prophase-I. During metaphase-I and metaphase-II, the protein remains associated with MTOCs, in a pericentrin dependent manner. Notably, knockdown of Nedd1 transcripts using specific siRNAs resulted in a high incidence (65-70%) of metaphase-I arrest. The arrested oocytes were characterized by disrupted meiotic spindle structure, reduced microtubule density and significant chromosome misalignment. Detection of MAD2 at kinetochores indicated an absence of stable chromosome-microtubule attachment as well as activation of the spindle assembly checkpoint (SAC). Importantly, the disruption of meiotic spindle stability was associated with decreased gamma-tubulin at MTOCs in NEDD1-depleted oocytes, as well as a high frequency of chromosome non-disjunction errors leading to aneuploidy (50%) in the oocytes that did progress to metaphase-II. This study demonstrates that NEDD1 is an essential component of acentriolar oocyte MTOCs, which functions in the regulation of meiotic spindle stability. Moreover, it underscores that disruption of spindle stability in oocytes can lead to chromosomes segregation errors that are not fully resolved by SAC.

Extending the knowledge in histochemistry and cell biology

Central to modern Histochemistry and Cell Biology stands the need for visualization of cellular and molecular processes. In the past several years, a variety of techniques has been achieved bridging traditional light microscopy, fluorescence microscopy and electron microscopy with powerful software-based post-processing and computer modeling. Researchers now have various tools available to investigate problems of interest from bird's- up to worm's-eye of view, focusing on tissues, cells, proteins or finally single molecules. Applications of new approaches in combination with well-established traditional techniques of mRNA, DNA or protein analysis have led to enlightening and prudent studies which have paved the way toward a better understanding of not only physiological but also pathological processes in the field of cell biology. This review is intended to summarize articles standing for the progress made in "histo-biochemical" techniques and their manifold applications.

State-of-the-art technologies, current opinions and developments, and novel findings: news from the field of histochemistry and cell biology

Investigations of cell and tissue structure and function using innovative methods and approaches have again yielded numerous exciting findings in recent months and have added important data to current knowledge, inspiring new ideas and hypotheses in various fields of modern life sciences. Topics and contents of comprehensive expert reviews covering different aspects in methodological advances, cell biology, tissue function and morphology, and novel findings reported in original papers are summarized in the present review.