The lamin code

Patient-Derived iPSCs Reveal Evidence of Telomere Instability and DNA Repair Deficiency in Coats Plus Syndrome

Coats plus (CP) syndrome is an inherited autosomal recessive condition that results from mutations in the conserved telomere maintenance component 1 gene (CTC1). The CTC1 protein functions as a part of the CST protein complex, a protein heterotrimer consisting of CTC1-STN1-TEN1 which promotes telomere DNA synthesis and inhibits telomerase-mediated telomere elongation. However, it is unclear how CTC1 mutations may have an effect on telomere structure and function. For that purpose, we established the very first induced pluripotent stem cell lines (iPSCs) from a compound heterozygous patient with CP carrying deleterious mutations in both alleles of CTC1. Telomere dysfunction and chromosomal instability were assessed in both circulating lymphocytes and iPSCs from the patient and from healthy controls of similar age. The circulating lymphocytes and iPSCs from the CP patient were characterized by their higher telomere length heterogeneity and telomere aberrations compared to those in control cells from healthy donors. Moreover, in contrast to iPSCs from healthy controls, the high levels of telomerase were associated with activation of the alternative lengthening of telomere (ALT) pathway in CP-iPSCs. This was accompanied by inappropriate activation of the DNA repair proteins γH2AX, 53BP1, and ATM, as well as with accumulation of DNA damage, micronuclei, and anaphase bridges. CP-iPSCs presented features of cellular senescence and increased radiation sensitivity. Clonal dicentric chromosomes were identified only in CP-iPSCs after exposure to radiation, thus mirroring the role of telomere dysfunction in their formation. These data demonstrate that iPSCs derived from CP patients can be used as a model system for molecular studies of the CP syndrome and underscores the complexity of telomere dysfunction associated with the defect of DNA repair machinery in the CP syndrome.

Interaction of tau with HNRNPA2B1 and N6-methyladenosine RNA mediates the progression of tauopathy

The microtubule-associated protein tau oligomerizes, but the actions of oligomeric tau (oTau) are unknown. We have used Cry2-based optogenetics to induce tau oligomers (oTau-c). Optical induction of oTau-c elicits tau phosphorylation, aggregation, and a translational stress response that includes stress granules and reduced protein synthesis. Proteomic analysis identifies HNRNPA2B1 as a principle target of oTau-c. The association of HNRNPA2B1 with endogenous oTau was verified in neurons, animal models, and human Alzheimer brain tissues. Mechanistic studies demonstrate that HNRNPA2B1 functions as a linker, connecting oTau with N6-methyladenosine (m6A) modified RNA transcripts. Knockdown of HNRNPA2B1 prevents oTau or oTau-c from associating with m6A or from reducing protein synthesis and reduces oTau-induced neurodegeneration. Levels of m6A and the m6A-oTau-HNRNPA2B1 complex are increased up to 5-fold in the brains of Alzheimer subjects and P301S tau mice. These results reveal a complex containing oTau, HNRNPA2B1, and m6A that contributes to the integrated stress response of oTau.

Role of Lamin A/C as Candidate Biomarker of Aggressiveness and Tumorigenicity in Glioblastoma Multiforme

Nuclear lamina components have long been regarded as scaffolding proteins, forming a dense fibrillar structure necessary for the maintenance of the nucleus shape in all the animal kingdom. More recently, mutations, aberrant localisation and deregulation of these proteins have been linked to several diseases, including cancer. Using publicly available data we found that the increased expression levels of the nuclear protein Lamin A/C correlate with a reduced overall survival in The Cancer Genome Atlas Research Network (TCGA) patients affected by glioblastoma multiforme (GBM). We show that the expression of the LMNA gene is linked to the enrichment of cancer-related pathways, particularly pathways related to cell adhesion and cell migration. Mimicking the modulation of LMNA in a GBM preclinical cancer model, we confirmed both in vitro and in vivo that the increased expression of LMNA is associated with an increased aggressiveness and tumorigenicity. In addition, delving into the possible mechanism behind LMNA-induced GBM aggressiveness and tumorigenicity, we found that the mTORC2 component, Rictor, plays a central role in mediating these effects.

The major evolutionary transitions and codes of life

Major evolutionary transitions as well as the evolution of codes of life are key elements in macroevolution which are characterized by increase in complexity Major evolutionary transitions ensues by a transition in individuality and by the evolution of a novel mode of using, transmitting or storing information. Here is where codes of life enter the picture: they are arbitrary mappings between different (mostly) molecular species. This flexibility allows information to be employed in a variety of ways, which can fuel evolutionary innovation. The collation of the list of major evolutionary transitions and the list of codes of life show a clear pattern: codes evolved prior to a major evolutionary transition and then played roles in the transition and/or in the transformation of the new individual. The evolution of a new code of life is in itself not a major evolutionary transition but allow major evolutionary transitions to happen. This could help us to identify new organic codes.

LMNA functions as an oncogene in hepatocellular carcinoma by regulating the proliferation and migration ability

The role of the LMNA gene in the development and progression of hepatocellular carcinoma (HCC) and the associated molecular mechanism is not yet clear. Therefore, the purpose of this study was to evaluate the relationship between LMNA and HCC. LMNA gene expression in normal tissues and corresponding tumours was evaluated and the Kaplan-Meier survival analysis was performed. Next, the LMNA gene was knocked out in the 293T and HepG2 cell lines using the CRISPR/Cas9 technique. Subsequently, the proliferation, migration and colony formation rate of the two LMNA knockout cell lines were analysed. Finally, the molecular mechanism affecting the tumorigenesis due to the loss of the LMNA gene was evaluated. The results showed that the LMNA gene was abnormally expressed in many tumours, and the survival rate of the HCC patients with a high expression of the LMNA gene was significantly reduced compared with the rate in patients with a low LMNA expression. The knockout of the LMNA gene in the HCC cell line HepG2 resulted in a decreased tumorigenicity, up-regulation of the P16 expression and down-regulation of the CDK1 expression. These findings suggested that LMNA might function as an oncogene in HCC and provided a potential new target for the diagnosis and treatment of HCC.

Lamin A involvement in ageing processes

Lamin A, a main constituent of the nuclear lamina, is the major splicing product of the LMNA gene, which also encodes lamin C, lamin A delta 10 and lamin C2. Involvement of lamin A in the ageing process became clear after the discovery that a group of progeroid syndromes, currently referred to as progeroid laminopathies, are caused by mutations in LMNA gene. Progeroid laminopathies include Hutchinson-Gilford Progeria, Mandibuloacral Dysplasia, Atypical Progeria and atypical-Werner syndrome, disabling and life-threatening diseases with accelerated ageing, bone resorption, lipodystrophy, skin abnormalities and cardiovascular disorders. Defects in lamin A post-translational maturation occur in progeroid syndromes and accumulated prelamin A affects ageing-related processes, such as mTOR signaling, epigenetic modifications, stress response, inflammation, microRNA activation and mechanosignaling. In this review, we briefly describe the role of these pathways in physiological ageing and go in deep into lamin A-dependent mechanisms that accelerate the ageing process. Finally, we propose that lamin A acts as a sensor of cell intrinsic and environmental stress through transient prelamin A accumulation, which triggers stress response mechanisms. Exacerbation of lamin A sensor activity due to stably elevated prelamin A levels contributes to the onset of a permanent stress response condition, which triggers accelerated ageing.

In search of a primitive signaling code

Cells must have preceded by simpler chemical systems (protocells) that had the capacity of a spontaneous self-assembly process and the ability to confine chemical reaction networks together with a form of information. The presence of lipid molecules in the early Earth conditions is sufficient to ensure the occurrence of spontaneous self-assembly processes, not defined by genetic information, but related to their chemical amphiphilic nature. Ribozymes are plausible molecules for early life, being the first small polynucleotides made up of random oligomers or formed by non-enzymatic template copying. Compartmentalization represents a strategy for the evolution of ribozymes; the attachment of ribozymes to surfaces, such as formed by lipid micellar aggregates may be particular relevant if the surface itself catalyzes RNA polymerization.It is conceivable that the transition from pre-biotic molecular aggregates to cellular life required the coevolution of the RNA world, capable of synthesizing specific, instead of statistical proteins, and of the Lipid world, with a transition from micellar aggregates to semipermeable vesicles. Small molecules available in the prebiotic inventory might promote RNA stability and the evolution of hydrophobic micellar aggregates into membrane-delimited vesicles. The transition from ribozymes catalyzing the assembly of statistical polypeptides to the synthesis of proteins, required the appearance of the genetic code; the transition from hydrophobic platforms favoring the stability of ribozymes and of nascent polypeptides to the selective transport of reagents through a membrane, required the appearance of the signal transduction code.A further integration between the RNA and Lipid worlds can be advanced, taking into account the emerging roles of phospholipid aggregates not only in ensuring stability to ribozymes by compartmentalization, but also in a crucial step of evolution through natural selection mechanisms, based on signal transduction pathways that convert environmental changes into biochemical responses that could vary according to the context. Here I present evidences on the presence of traces of the evolution of a signal transduction system in extant cells, which utilize a phosphoinositide signaling system located both at nucleoplasmic level as well as at the plasma membrane, based on the very same molecules but responding to different rules. The model herewith proposed is based on the following assumptions on the biomolecules of extant organisms: i) amphiphils can be converted into structured aggregates by hydrophobic forces thus giving rise to functional platforms for the interaction of other biomolecules and to their compartmentalization; ii) fundamental biochemical pathways, including protein synthesis, can be sustained by natural ribozymes of ancient origin; iii) ribozymes and nucleotide-derived coenzymes could have existed long before protein enzymes emerged; iv) signaling molecules, both derived from phospholipids and from RNAs could have guided the evolution of complex metabolic processes before the emergence of proteins.