[Development of the human eye]. / Entwicklung des menschlichen Auges.

The development of the human eye requires a coordinated interplay between cells from different origins. The optic cup which is neuroectodermal in origin and derives from the neural tube, gives rise to the neuronal retina, the retinal pigmented epithelium, the epithelial layers of ciliary body and iris, and the iris musculature. The lens which is displaced into the optic cup during development originates from the surface ectoderm. Cells of the neural crest provide the ocular mesenchyme while ocular blood vessels are of mesodermal origin. The basic morphogenetic processes of eye development are completed at the end of the second month of embryonic life. However, for correct functioning further maturation processes are required which are not completed before birth or several months after. Examples are aqueous humor circulation, maturation of cones in the foveola, myelination of optic nerve axons and completion of the retinal vasculature.

Proteins with an endostatin-like domain in a mouse model of oxygen-induced retinopathy.

Neovascularization in the retinopathy of prematurity (ROP) mouse eye is a self-limiting phenomenon. Free endostatin is known to be anti-angiogenic. In this study, we identified the localization of endostatin-like protein (ELP) sequences and investigated their possible role in this process. ROP was induced in C57Bl/6 mice and the eyes observed 1-11 days after termination of high oxygen supply (P13-P21). Sagittal sections and retinal flatmounts were double-stained with antibodies against a protein-sequence of endostatin, vascular endothelial growth factor (VEGF), lectin, and smooth-muscle alpha actin. The fluorescence was visualized by traditional and confocal microscopy. Intense staining for VEGF in the inner retina was limited to the early stages of neovascularization and diminished at P19-P21. In contrast, staining for ELPs appeared at P15 around the newly formed vessels and remained even after degeneration of their endothelial cells. Staining of the inner retinal vasculature for ELPs was restricted to P17-P19, the known maximum of the neovascular response. Outer retinal vessels did not show presence of ELPs at any time. Our study demonstrates that ELPs, absent at the beginning of neovascular sprouting, increases with the amount of neovascularization and thus, varies reciprocally to VEGF in the time period investigated. ELPs remain during the regression of the vessels and might therefore play an important role in the self-limiting process of ROP neovascularization.

[The role of myocilin in the pathogenesis of primary open-angle glaucoma]. / Die Rolle von Myocilin bei der Pathogenese des primären Offenwinkelglaukoms.

Mutations in myocilin are responsible for autosomal-dominant inherited juvenile open-angle glaucoma and some subgroups of adult-onset glaucoma (POAG). Myocilin is a secreted glycoprotein with a molecular weight of approximately 55-57 kDa that forms dimers and multimers. Structural motives are domains that have similarities with myosin and olfactomedin, a signalling sequence as well as a leucine zipper at the N-terminus of myocilin. Most mutations that were identified in patients with POAG are localized in the olfactomedin domain which is highly conserved between species. In the eye, myocilin is highly expressed in the trabecular meshwork (TM), the sclera, the ciliary body and the iris, lower amounts are seen in the retina and the optic nerve. In addition, secreted myocilin is detected in the aqueous humor. In the chamber angle, myocilin is associated with fibrillar components of the extracellular matrix in the cribriform portion of the TM. Myocilin binds specifically to the HepII domain of fibronectin. In organ cultures of perfused anterior eye segments, recombinant myocilin increases outflow resistance. In cultured TM cells, myocilin is induced by treatment with dexamethasone in a similar time course as observed in steroid-induced glaucoma. Myocilin is also induced by transforming growth factor-beta (TGF-beta) and mechanical stress. Mice with a targeted disruption of the myocilin gene do not express a phenotype. Experimental data indicate that mutated myocilin is not secreted and accumulates in cells which might critically impair the function of the TM.

Transcriptional activation of the haem oxygenase-1 gene by cGMP via a cAMP response element/activator protein-1 element in primary cultures of rat hepatocytes.

The expression of the rate-limiting enzyme of haem degradation, haem oxygenase-1 (HO-1), can be induced by various stimuli, including lipopolysaccharide, tumour necrosis factor alpha and NO. The NO signal can be transmitted by cGMP, therefore this study was aimed at testing the activation of the HO-1 gene by cGMP. In primary cultures of rat hepatocytes, both HO-1 mRNA and protein were induced by the NO donor sodium nitroprusside and 8-bromo-cGMP. The HO-1 mRNA induction by cGMP was prevented by the specific protein kinase G inhibitor KT5823. The cGMP-dependent HO-1 mRNA induction was dose-dependent and transcriptionally regulated, as determined by studies with actinomycin D and a nuclear run-on assay. Cycloheximide lowered the cGMP-dependent induction of HO-1 mRNA to about one half. Luciferase reporter constructs driven by about 800 bp of the 5'-flanking region of the rat HO-1 gene were transiently transfected into primary rat hepatocytes; 8-bromo-cGMP caused a 6-fold induction, which was obliterated by deletion and mutation of the cAMP response element/activator protein-1 (CRE/AP-1) (-665/-654) site. Thus HO-1 induction by cGMP appears to be stimulated by the protein kinase G pathway and may be mediated mainly via a CRE/AP-1 element in the rat HO-1 promoter.