Twist is substrate for caspase cleavage and proteasome-mediated degradation.

Twist is a member of the basic helix-loop-helix family of transcription factors. An aberrant Twist expression has been found in diverse types of cancer, including sarcomas, carcinomas and lymphomas, supporting a role for Twist in tumor progression. Twist is known to be essential for mesodermal development. However, since a prolonged Twist expression results in a block of muscle, cartilage and bone differentiation, Twist has to be excluded from somites during late embryogenesis for terminal differentiation to occur. This implies that Twist expression must be target of a tight control. Here we provide evidence that Twist undergoes post-transcriptional regulation. Twist is substrate for cleavage by caspases during apoptosis and its cleavage results in ubiquitin-mediated proteasome degradation. Our findings suggest that Twist post-transcriptional regulation may play an important role in tissue determination and raise the possibility that alterations in the protein turnover may account for Twist overexpression observed in tumors.

Electrophoretic and immunochemical study of collagens from Sepia officinalis cartilage.

Electrophoretic and Western blot studies were conducted on collagen fractions extracted from Sepia officinalis (cuttlefish) cartilage using a modified salt precipitation method developed for the isolation of vertebrate collagens. The antibodies used had been raised in rabbit against the following types of collagen: Sepia I-like; fish I; human I; chicken I, II, and IX; rat V; and calf IX and XI. The main finding was that various types of collagen are present in Sepia cartilage, as they are in vertebrate hyaline cartilage. However, the main component of Sepia cartilage is a heterochain collagen similar to vertebrate type I, and this is associated with minor forms similar to type V/XI and type IX. The cephalopod type I-like heterochain collagen can be considered a first step toward the evolutionary development of a collagen analogous to the typical collagen of vertebrate cartilage (type II homochain). The type V/XI collagen present in molluscs, and indeed all phyla from the Porifera upwards, may represent an ancestral collagen molecule conserved relatively unchanged throughout evolution. Type IX-like collagen seems to be essential for the formation of cartilaginous tissue.

Immunohistochemical study of collagens of the extracellular matrix in cartilage of Sepia officinalis.

We used various anti-collagen antibodies to perform indirect immunofluorescent staining of cartilage sections from cuttlefish (S. officinalis). On ultrathin sections and collagen fibril preparations from the same tissue, we performed immunostaining with colloidal gold. The extracellular matrix (ECM) of S. officinalis cartilage reacted intensely and homogeneously with an antibody directed against type I-like collagen isolated from the cartilage of cuttlefish and with anti-rat type V collagen antibody. A weak reaction was observed with anti-fish and anti-chicken type I collagen antibodies, while no reaction was observed with anti-rat type I and anti calf type II collagen antibodies. Anti-chicken type II, anti calf type IX and type XI collagen antibodies reacted weakly with ECM, while stained cell bodies and cell processes reacted more intensely. A similar pattern of reaction was observed on cartilage section and isolated collagen fibrils prepared for electron microscopy. These findings suggest that ECM of cuttlefish cartilage may be composed of molecules similar to the type I, type V, type IX and type XI collagen molecules of vertebrates. Cephalopods have evolved a cartilage of structure and macromolecular organisation similar to that of vertebrate cartilage. However, the main molecular components of S. officinalis cartilage--type I-like and type V collagens--differ from those of vertebrate cartilage. We suggest that this type I-like collagen can be considered an initial step toward the evolution of type II collagen typical of vertebrates.

Use of rotary shadowing electron microscopy to investigate the collagen fibrils in the extracellular matrix of cuttle-fish (Sepia officinalis) and chicken cartilage.

Collagen fibrils isolated from sternal cartilage of chick embryo and chondrocranium of cuttle-fish (Sepia officinalis) were examined with the electron microscope after rotary showing. The aim was to determine whether collagen fibrils from S. officinalis cartilage contained collagen molecules similar to the type IX collagen of vertebrate cartilage. Cartilage from both sources presented a highly variable appearance and only occasionally did preparations contain fibrils having the structure described by Vaughan et al. (1988) for vertebrate cartilage. Subsequent electron microscope investigation of collagen samples during the various stages of fibril preparation showed that the method did not yield reproducible results, and that is altered the morphology of the isolated structures. It was not, therefore, possible to confirm the hypothesis that collagen molecules with a morphology similar to that type IX vertebrate collagen are a component of the extracellular matrix of cephalopod cartilage.

All-optical switching in distributed-feedback muiltiple-quantum-well waveguides.

We discuss experimental results that demonstrate all-optical switching and pulse-routing functionality, at 1.55 um, of nonlinear multiple-quantum-well waveguides equipped with a Bragg grating. Basing on the nonlinear Time-Domain Beam Propagation Method, the switching behavior has been theoretically investigated using a model, developed as part of this work.

All-optical switching and pulse routing in a distributed-feedback waveguide device.

Results of all-optical switching and pulse-routing experiments with a distributed-feedback multiple-quantum-well (MQW) nonlinear waveguide, operating at 1.55microm , are reported. The MQW material has been engineered, through the controlled introduction of defects, to lower the carrier lifetime from 2.5 ns to 280 ps. The energy required for switching is of the order of 1 pJ or less, the switching time is ~600 ps , and the on-off contrast exceeds 17 dB.

The ultrastructure of chondrocytes in the cartilage of Sepia officinalis and Octopus vulgaris (Mollusca, Cephalopoda).

Thin sections of cartilage from the chondrocranium of cuttle fish and octopus were examined using the transmission electron microscope. It was found that cephalopod chondrocytes differed considerably from the chondrocytes of vertebrate cartilage; in particular they possessed many long and ramifying cytoplasmic processes and had an ultrastructure typical of protein-secreting cells. They did not, however, contain secretory granules; while vesicles and rough endoplasmic reticulum cisternae seemed to open directly to the cell surface. The cell body and processes contained cytoskeletal structures: microtubules were easily recognized, but intermediate and thin filaments were difficult to make out as they were frequently clumped into bundles. Some chondrocytes contained conspicuous accumulations of hemocyanin. The cytoplasmic processes possessed intercellular contacts similar to gap junctions. Also present on processes and the cell body were cell-extracellular matrix focal adhesions. The chondrocytes were not polarized or arranged in any preferential spatial order, however, with their processes they formed a three-dimensional network throughout the cartilage tissue. Ultrastructural findings are discussed in relation to the singular morphofunctional characteristics of cephalopod cartilage which shares features with both the cartilage and bone of vertebrates.

Inhibition of tumorigenicity in lung adenocarcinoma cells by c-erbB-2 antisense expression.

The lung carcinoma cell line Calu3, which overexpresses the c-erbB-2 oncogene, was stably transfected with antisense (AS) cDNA constructs encompassing different regions of the c-erbB-2 gene. Transfected cells were analyzed for their tumorigenic properties in vitro and in nude mice. Two independent clones, AS F1 (low erbB-2 expressor) and AS B12 (high erbB-2 expressor), as well as the polyclonal Calu3/AS 5', were selected for these analyses. In Calu3/AS 5' transfected cells and in the AS F1 clone, c-erbB-2 RNA and protein levels were lower than those detected in the parental cell line and the AS B12 clone. Anchorage-independent growth and tumor take were also significantly reduced. Furthermore, cells derived from primary tumors of Calu3/AS 5', AS F1 and AS B12 lost the AS c-erbB-2 DNA insert but retained the gene for G418 resistance. Our results suggest that a correlation between c-erbB-2 overexpression and tumorigenicity may exist in the Calu3 lung carcinoma cell line.