"Untersuchungen zur 3D-Feinstruktur der Cilienregion in den Photorezeptoren der Europäischen Sardelle."
3D-ultrastructural investigations of the ciliary region of photoreceptors in the European anchovy.
The present study deals with the 3D-ultrastructure of photoreceptor outer segments in the European anchovy (Engraulis encrasicolus, Engraulididae, Teleostei). The main focus is put on the investigation of ciliar differentiation of long and short cones at the ventro-temporal retinal margin.
On the basis of precisely oriented, mostly complete ultrathin section series computer-aided 3-dimensional figures were generated (AMIRA®), illustrated and evaluated volumetrically. In addition, essential ultrastructural details were recorded.
These data were discussed and compared with existing results with special regard to morphogenesis of differentiating cones.
Initially, the long cone outer segments develop as tangentially oriented membranous lamellae. During differentiation, the outer segments are restrained between the pigment epithelial wedges and are forced into a radial overturning. The ciliary stalk is positioned laterally in the ellipsoid and elongates sklerad to an accessory outer segment that acts as a pillar for the real outer segment.
By contrast, the ciliary stalks of short cones do not form an accessory outer segment and are located in the middle of the ellipsoid. The membranous lamellae rise from the ciliar basis tangentially oriented but further apical there is a slight overturning. From the third cone row the lamellae are erected furthermore and are radially oriented in completely differentiated short cones. Obviously, their lamellar turnaround is effected without any sterical influence on the part of the pigment epithelium. Not until the short cones are completely differentiated the pigment epithelial wedges grow towards their outer segments splitting them into two lobes.