Identification of the antigen recognized by the monoclonal antibody BU31 as lamins A and C

Differential expression of nuclear lamin subtypes in the neural cells of the adult rat cerebral cortex

Lamins are type V intermediate filament proteins that are located beneath the inner nuclear membrane. In mammalian somatic cells, LMNB1 and LMNB2 encode somatic lamins B1 and B2, respectively, and the LMNA gene is alternatively spliced to generate somatic lamins A and C. Mutations in lamin genes have been linked to many human hereditary diseases, including neurodegenerative disorders. Knowledge about lamins in the nervous system has been accumulated recently, but a precise analysis of lamin subtypes in glial cells has not yet been reported. In this study we investigated the composition of lamin subtypes in neurons, astrocytes, oligodendrocyte-lineage cells, and microglia in the adult rat cerebral cortex using an immunohistochemical staining method. Lamin A was not observed in neurons and glial cells. Lamin C was observed in astrocytes, mature oligodendrocytes and neurons, but not observed in oligodendrocyte progenitor cells. Microglia also did not stain positive for lamin C which differed from macrophages, with lamin C positive. Lamin B1 and B2 were observed in all glial cells and neurons. Lamin B1 was intensely positive in oligodendrocyte progenitor cells compared with other glial cells and neurons. Lamin B2 was weakly positive in all glial cells compared to neurons. Our current study might provide useful information to reveal how the onset mechanisms of human neurodegenerative diseases are associated with mutations in genes for nuclear lamin proteins.

Transcriptional reprogramming in cellular quiescence

Most cells in nature are not actively dividing, yet are able to return to the cell cycle given the appropriate environmental signals. There is now ample evidence that quiescent G0 cells are not shut-down but still metabolically and transcriptionally active. Quiescent cells must maintain a basal transcriptional capacity to maintain transcripts and proteins necessary for survival. This implies a tight control over RNA polymerases: RNA pol II for mRNA transcription during G0, but especially RNA pol I and RNA pol III to maintain an appropriate level of structural RNAs, raising the possibility that specific transcriptional control mechanisms evolved in quiescent cells. In accordance with this, we recently discovered that RNA interference is necessary to control RNA polymerase I transcription during G0. While this mini-review focuses on yeast model organisms (Saccharomyces cerevisiae and Schizosaccharomyces pombe), parallels are drawn to other eukaryotes and mammalian systems, in particular stem cells.

The role of the nuclear lamina in cancer and apoptosis

Not long after the discovery of lamin proteins, it became clear that not all lamin subtypes are ubiquitously expressed in cells and tissues. Especially, A-type lamins showed an inverse correlation with proliferation and were thus initially called statins. Here we compare the findings of both A- and B-type lamin expression in various normal tissues and their neoplastic counterparts. Based on immunocytochemistry it becomes clear that lamin expression patterns are much more complicated than initially assumed: while normally proliferative cells are devoid of A-type lamin expression, many neoplastic tissues do show prominent A-type lamin expression. Conversely, cells that do not proliferate can be devoid of lamin expression. Yet, within the different types of tissues and tumors, lamins can be used to distinguish between tumor subtypes. The link between the appearance of A-type lamins in differentiation and the appearance of A-type lamins in a tumor likely relates the proliferative capacity of the tumor to its differentiation state.While lamins are targets for degradation in the apoptotic process, and accordingly are often used as markers for apoptosis, intriguing studies on an active role of lamins in the initiation or the prevention of apoptosis have been published recently and give rise to a renewed interest in the role of lamins in cancer.

Differential expression of nuclear lamin, the major component of nuclear lamina, during neurogenesis in two germinal regions of adult rat brain

Lamins are major structural proteins of the nuclear envelope. Three lamin subtypes, A/C, B1 and B2, predominate in mammalian somatic cells. While the expression levels of lamins in several tissues are known to change during cell differentiation, lamin expression is poorly understood in the nervous system. To investigate the expression of lamins during neuronal differentiation in the mammalian adult brain, we performed immunohistochemical studies on lamins A/C, B1 and B2 in two neurogenic regions of rat brain: the subgranular zone of the dentate gyrus and the subventricular zone of the lateral ventricle. In particular, three types of cells were analysed using confocal microscopy: GFAP-positive cells as primary progenitor (stem) cells, PSA-NCAM-positive cells as subsequent neuronal progenitor cells, and NeuN-positive mature neurons. GFAP-positive cells possesed lamin A/C (++), B1 (++) and B2 (++), PSA-NCAM-positive cells possessed lamin A/C (-), B1 (+++) and B2 (+), and mature neurons possessed lamin A/C (++), B1 (+) and B2 (+++), in both neurogenic regions. These observations showed that the compositions of expressing lamin subtypes are distinct in particular differentiation stages during neurogenesis in the adult rat brain. Our results suggest that the alteration of nuclear lamina structure is coupled with the progression of neuronal differentiation.

The nuclear lamina and its proposed roles in tumorigenesis: Projection on the hematologic malignancies and future targeted therapy

The nuclear lamina, a network of lamin filaments and lamin-associated proteins, is located between the inner nuclear membrane and the peripheral chromatin. The nuclear lamina is involved in numerous nuclear functions including maintaining nuclear shape, determining nuclear positioning, organizing chromatin and regulating the cell cycle, DNA replication, transcription, cell differentiation, apoptosis, and aging. Alterations in the composition of nuclear lamins and their associated proteins are currently emerging as an additional event involved in malignant transformation, tumor propagation and progression, thus identifying potential novel targets for future anti-cancer therapy. Here, we review the current knowledge on lamin expression patterns in cells of hematologic malignancies and give an overview on the roles of the nuclear lamina proteins in heterochromatin organization, apoptosis, and aging with special emphasis on the relevance in cancer development.

Molecular aetiology and pathogenesis of basal cell carcinoma

Recent insights into the cell biology of the epidermis and its appendages are transforming our understanding of the pathogenesis of basal cell carcinoma (BCC). The significant progress that has been made warrants a comprehensive review of the molecular and cellular pathology of BCC. The items addressed include environmental and genetic risk factors, the biology of the putative precursor cell(s), and the contribution of aberrations in processes such as apoptosis, cell proliferation, differentiation and signalling to carcinogenesis. Furthermore, established and novel treatment modalities are discussed with particular attention to future biological approaches.

Molecular Mechanisms, Diagnosis, and Rational Approaches to Management of and Therapy for Charcot-Marie-Tooth Disease and Related Peripheral Neuropathies

During the last decade, 18 genes and 11 additional loci harboring candidate genes have been associated with Charcot-Marie-Tooth disease (CMT) and related peripheral neuropathies. Ten of these 18 genes have been identified in the last 2 years. This phenomenal pace of CMT gene discovery has fomented an unprecedented explosion of information regarding peripheral nerve biology and its pathologic manifestations in CMT. This review integrates molecular genetics with the clinical phenotypes and provides a flowchart for molecular-based diagnostics. In addition, we discuss rational approaches to molecular therapeutics, including novel biologic molecules (eg, small interfering ribonucleic acid [siRNA], antisense RNA, and ribozymes) that potentially could be used as drugs in the future. These may be applicable in attempts to normalize gene expression in cases of CMT type 1A, wherein a 1.5 Mb genomic duplication causes an increase in gene dosage that is associated with the majority of CMT cases. Aggresome formation by the PMP22 gene product, the disease-associated gene in the duplication cases, could thus be avoided. We also discuss alternative therapeutics, in light of other neurodegenerative disorders, to disrupt such aggresomes. Finally, we review rational therapeutic approaches, including the use of antioxidants such as vitamin E, coenzyme Q10, or lipoic acid to relax potential oxidative stress in peripheral nerves, for CMT management.

Ectopic overexpression of Drosophila lamin C is stage-specific lethal

To gain insight into the function of the developmentally regulated A-type lamins we transformed Drosophila melanogaster with a construct containing the hsp70 promoter followed by the Drosophila lamin C (an analog of vertebrate A-type lamins) cDNA. Lamin C was expressed ectopically after heat shock of embryos and localized to the nucleus. No phenotypic change was observed after lamin C expression in embryos that normally do not contain lamin C. However, ectopic expression of lamin C during most larval (but not pupal) stages stalled growth, inhibited ecdysteroid signaling (in particular during the larval-prepupal transition), resulted in development of melanotic tumors, and finally caused death. During pupation in control animals, when massive apoptosis of larval tissues takes place, lamin C is proteolyzed into a fragment with a size similar to that predicted by caspase cleavage. The ectopically expressed lamin C is identically cleaved, resulting in a large increase of the steady-state level of the lamin C fragment. A null mutation of the dcp-1 gene, one of the two known Drosophila caspase genes, also results in development of melanotic tumors and larval death, suggesting that the ectopically expressed lamin C inhibits apoptosis through competitive inhibition of caspase activity.

Dynamic repositioning of genes in the nucleus of lymphocytes preparing for cell division

We show that several transcriptionally inactive genes localize to centromeric heterochromatin in the nucleus of cycling but not quiescent (noncycling) primary B lymphocytes. In quiescent cells, centromeric repositioning of inactive loci was induced after mitogenic stimulation. A dynamic repositioning of selected genes was also observed in developing T cells. Rag and TdT loci were shown to relocate to centromeric domains following heritable gene silencing in primary CD4+8+ thymocytes, but not in a phenotypically similar cell line in which silencing occurred but was not heritable. Collectively, these data indicate that the spatial organization of genes in cycling and noncycling lymphocytes is different and that locus repositioning may be a feature of heritable gene silencing.

Nuclear lamins: their structure, assembly, and interactions

Nuclear lamins are intermediate filament-type proteins that are the major building blocks of the nuclear lamina, a fibrous proteinaceous meshwork underlying the inner nuclear membrane. Lamins can also be localized in the nuclear interior, in a diffuse or spotted pattern. Nuclei assembled in vitro in the absence of lamins are fragile, indicating that lamins mechanically stabilize the cell nucleus. Available evidence also indicates a role for lamins in DNA replication, chromatin organization, spatial arrangement of nuclear pore complexes, nuclear growth, and anchorage of nuclear envelope proteins. In this review we summarize the current state of knowledge on the structure, assembly, and possible functional roles of nuclear lamins, emphasizing the information concerning the ability of nuclear lamins to self-assemble into distinct oligomers and polymers.

Cell cycle changes in A-type lamin associations detected in human dermal fibroblasts using monoclonal antibodies

A new panel of anti-A-type lamin monoclonal antibodies was generated. Epitope mapping was performed by immunoblotting against GST-lamin fusion peptides. Epitopes were mapped to four different regions of human lamin A and three different regions of human lamin C. The distribution of A-type lamins was compared with the distribution of the proliferation marker Ki67 in proliferating and quiescent cultures of human dermal fibroblasts (HDFs) using a double indirect immunofluorescence assay. Antibodies that had been mapped to a region of the lamin C tail stained the nuclear envelope of proliferating and quiescent cells equally brightly. In contrast, antibodies recognizing epitopes in the head domain and rod domain of lamins A and C and the tail domain of lamin A stained the nuclear envelope of quiescent cells strongly but reacted poorly or not at all with the nuclear envelope of proliferating cells. Changes in the level of expression of lamins A and C were not detected in immunoblotting assays. However, epitope masking was revealed, and this occurred by two distinct mechanisms. Epitope masking in the head domain of lamins A and C occurred as a result of protein phosphorylation. Epitope masking in the rod domain of lamins A and C and in the tail domain of lamin A occurred through a physical association between the lamin and chromatin and/or other nuclear proteins. The cell cycle timing of epitope masking was investigated in HDFs that had been restimulated after serum starvation. Extensive epitope masking in restimulated cells only occurred after cells had passed through mitosis. These results are consistent with the hypothesis that rearrangement of A-type lamin filaments, as cells progress from a quiescent to a proliferating state, results in altered lamina associations.