Inner/Outer Nuclear Membrane Fusion in Nuclear Pore Assembly: Biochemical Demonstration and Molecular Analysis

The nuclear pore complex (NPC) is characterized by a long-lived membrane-lined channel connecting the inner and outer nuclear membranes. This stabilized membrane channel, within which the nuclear pore is built, has little evolutionary precedent. In this report we demonstrate and map the inner/outer nuclear membrane fusion in NPC assembly

Tracking Endogenous Amelogenin and Ameloblastin In Vivo

Research on enamel matrix proteins (EMPs) is centered on understanding their role in enamel biomineralization and their bioactivity for tissue engineering. While therapeutic application of EMPs has been widely documented, their expression and biological function in non-enamel tissues is unclear. Our first aim was to screen for amelogenin (AMELX) and ameloblastin (AMBN) gene expression in mandibular bones and soft tissues isolated from adult mice (15 weeks old). Using RT-PCR, we showed mRNA expression of AMELX and AMBN in mandibular alveolar and basal bones and, at low levels, in several soft tissues; eyes and ovaries were RNA-positive for AMELX and eyes, tongues and testicles for AMBN. Moreover, in mandibular tissues AMELX and AMBN mRNA levels varied according to two parameters: 1) ontogenic stage (decreasing with age), and 2) tissue-type (e.g. higher level in dental epithelial cells and alveolar bone when compared to basal bone and dental mesenchymal cells in 1 week old mice). In situ hybridization and immunohistodetection were performed in mandibular tissues using AMELX KO mice as controls. We identified AMELX-producing (RNA-positive) cells lining the adjacent alveolar bone and AMBN and AMELX proteins in the microenvironment surrounding EMPs-producing cells. Western blotting of proteins extracted by non-dissociative means revealed that AMELX and AMBN are not exclusive to mineralized matrix; they are present to some degree in a solubilized state in mandibular bone and presumably have some capacity to diffuse. Our data support the notion that AMELX and AMBN may function as growth factor-like molecules solubilized in the aqueous microenvironment. In jaws, they might play some role in bone physiology through autocrine/paracrine pathways, particularly during development and stress-induced remodeling

Age-related changes of nuclear architecture in Caenorhabditis elegans

Mutations in lamins cause premature aging syndromes in humans, including the Hutchinson–Gilford Progeria Syndrome (HGPS) and Atypical Werner Syndrome. It has been shown that HGPS cells in culture undergo age-dependent progressive changes in nuclear architecture. However, it is unknown whether similar changes in nuclear architecture occur during the normal aging process. We have observed that major changes of nuclear architecture accompany Caenorhabditis elegans aging. We found that the nuclear architecture in most nonneuronal cell types undergoes progressive and stochastic age-dependent alterations, such as changes of nuclear shape and loss of peripheral heterochromatin. Furthermore, we show that the rate of these alterations is influenced by the insulin/IGF-1 like signaling pathway and that reducing the level of lamin and lamin-associated LEM domain proteins leads to shortening of lifespan. Our work not only provides evidence for changes of nuclear architecture during the normal aging process of a multicellular organism, but also suggests that HGPS is likely a result of acceleration of the normal aging process. Because the nucleus is vital for many cellular functions, our studies raise the possibility that the nucleus is a prominent focal point for regulating aging

Matefin/SUN-1 is a nuclear envelope receptor for CED-4 during Caenorhabditis elegans apoptosis

In Caenorhabditis elegans, the antiapoptotic protein CED-9 is localized at the mitochondria, where it binds the proapoptotic protein CED-4. Induction of apoptosis begins when the proapoptotic protein EGL-1 is expressed and binds CED-9. The binding of EGL-1 to CED-9 releases CED-4 from CED-9 and causes the activation of the caspase CED-3. Upon its release from CED-9, CED-4 rapidly translocates to the nuclear envelope (NE) in a CED-3-independent manner. However, the identity of the NE receptor for CED-4 and its possible role in the execution of apoptosis has remained unknown. Here, we show that the inner nuclear membrane SUN-domain protein matefin/SUN-1 is the NE receptor for CED-4. Our data demonstrate that matefin/SUN-1 binds CED-4 and is specifically required for CED-4 translocation and maintenance at the NE. The role of matefin/SUN-1 in the execution of apoptosis is further suggested by the significant reduction in the number of apoptotic cells in the organism after matefin/SUN-1 down-regulation by RNAi. The finding that matefin/SUN-1 is required for the execution of apoptosis adds an important link between cytoplasmic and nuclear apoptotic events

A laminopathic mutation disrupting lamin filament assembly causes disease-like phenotypes in Caenorhabditis elegans

Mutations in human LMNA cause Emery-Dreifuss muscular dystrophy; however, a mechanistic link between the effect of mutations on lamin filament assembly and disease phenotype has not been established. Here we show that changes in lamin filament structure translate into disease phenotypes in Caenorhabditis elegans by altering the character of the nuclear lamina

Ce-emerin and LEM-2: essential roles in Caenorhabditis elegans development, muscle function, and mitosis

ETOC: Caenorhabditis elegans lacking both Ce-emerin and LEM-2 show that these proteins are essential for development of specific lineages, mitosis in somatic cells, and smooth muscle activity. Reduced life span and smooth muscle activity of LEM-2–null worms predicts human LEM2 gene links to diseases more severe than Emery-Dreifuss muscular dystrophy