Characterization of hydra type IV collagen. Type IV collagen is essential for head regeneration and its expression is up-regulated upon exposure to glucose

Hydra vulgaris mesoglea is a primitive basement membrane that also exhibits some features of an interstitial matrix. We have characterized cDNAs that encode the full-length hydra alpha1(IV) chain. The 5169-base pair transcript encodes a protein of 1723 amino acids, including an interrupted 1455-residue collagenous domain and a 228-residue C-terminal noncollagenous domain. N-terminal sequence analyses of collagen IV peptides suggest the molecule is homotrimeric. Denatured hydra type IV collagen protein occurs as dimers and higher order aggregates held together by nonreducible cross-links. Hydra collagen IV exhibits no functional evidence for the presence of a 7 S domain. Type IV collagen is expressed by the ectoderm along the entire longitudinal axis of the animal but is most intense at the base of the tentacles at the site of battery cell transdifferentiation. Antisense studies show that inhibition of collagen IV translation causes a blockage in head regeneration, indicating its importance in normal hydra development. Exposure of adult hydra to 15 mm glucose resulted in up-regulation of type IV collagen mRNA levels within 48 h and significant thickening of the mesoglea within 14 days, suggesting that basement membrane thickening seen in diabetes may be, in evolutionary terms, an ancient glucose-mediated response.

A comparison of the effectiveness of dentine bonding agents

Tensile and shear bond strengths between prepared surfaces of coronal dentine and cores of composite materials using different bonding systems were determined. Control procedures demonstrated that tensile bond strengths were approximately doubled by the use of bonding agents in systems requiring initial cleansing or etching of dentine. Similar increases were found in shear bond strengths. When bonding to different depths of dentine was compared shear and tensile bond strengths to the more occlusal dentine were greater than to more pulpally placed dentine. The factors which appear to affect bond strength under laboratory conditions are: etching of dentine (but beware of this procedure clinically); the smear layer and its removal; polymerization shrinkage of composite materials; the depth and plane of bonded dentine; the use of fresh or stored dentine; and the structure of the treated dentine.