Tissue factor expression in newt iris coincides with thrombin activation and lens regeneration

Lens regeneration in adult salamanders occurs at the pupillary margin of the mid-dorsal iris where pigmented epithelial cells (PEC) re-enter the cell cycle and transdifferentiate into lens. It is not understood how the injury caused by removal of the lens (lentectomy) in one location is linked to initiating the response in a different spatial location (dorsal iris) and to this particular sector. We propose that the blood provides a link between the localised coagulation and signal transduction pathways that lead to regeneration. A transmembrane protein (tissue factor) is expressed in a striking patch-like domain in the dorsal iris of the newt that localises coagulation specifically to this location, but is not expressed in the axolotl, a related species that does not show thrombin activation after lentectomy and cannot regenerate its lens. Our hypothesis is that tissue factor expression localises the initiation of regeneration through the activation of thrombin and the recruitment of blood cells, leading to local growth factor release. This is the first example of gene expression in a patch of cells that prefigures the location of a regenerative response, and links the immune system with the initiation of a regenerative program.     

Study of two cases of ring 13 chromosome using high-resolution banding.

The chromosomes of two patients with ring 13 (r13) were studied using high-resolution RBG banding of prometaphase cells. The rings of the two patients differ slightly in breakpoints. Cell with multiple single, double-sized rings, quadruple-sized rings, rod- and ring-shaped fragments, and fragments showing varied states of condensation were seen, as were cells monosomic for chromosome 13. The evolution of these cell lines as a result of sister chromatid exchange, nondisjunction, ring breakage, and premature chromosome condensation is discussed. Clinical features of these patients reflect the heterogeneity of phenotype for r13 patients. Each case includes a feature of trisomy 13. The significance of mosaicism of cell lines in patients bearing ring chromosomes is considered with respect to variation in clinical findings.     

The conformation of calmodulin: a substantial environmentally sensitive helical transition in Ca4-calmodulin with potential mechanistic function

The conformation of Ca4-calmodulin in solution, as assessed by far-UV peptide circular dichroism, contains significantly less alpha-helix than the proposed X-ray crystal structure. We now show that Ca4-calmodulin adopts significant additional helical structure in solution in the presence of a helicogenic solvent (50%, v/v, aqueous 2,2,2-trifluoroethanol or 50%, v/v, methylpentane-5,5-diol). We suggest that the long continuous helix (residues 66-92 of the crystal structure) is not necessarily a normal feature of the calmodulin structure in solution, and may be due in part to the conditions of crystallisation. This result is supported by time-resolved tyrosine fluorescence anisotropy studies indicating that Ca4-calmodulin in solution is an essentially compact globular structure which undergoes isotropic rotational motion. We conclude that, under appropriate ionic and apolar environmental conditions, Ca4-calmodulin undergoes a substantial helical transition, which may involve residues in the central region of the molecule. Such a transition could have an important function in determining specificity and affinity in interactions of calmodulin with different target sequences of Ca2+-dependent regulatory enzymes.     

Acanthocephaloides cyrusi n. sp. (Acanthocephala: Arhythmacanthidae) from southeast African teleost fishes

A new species,Acanthocephaloides cyrusi, is described from the fishesSolea bleekeri andPomadasys commersoni from Lake St. Lucia, Natal, South Africa. It is distinguished from the other species in the genus by the more marked sexual dimorphism in length, the arrangement of hooks, the proboscis with the longest hooks at the anterior-most extremity and the greater size of the proboscis hooks and body spines. An acanthella, which may represent this species, was found in the tanaidApseudes digitalis.