Actions of surface groups on the circle

We cover some topics on rigidity for actions of surface groups on the circle. Group actions on the circle are classified up to semi-conjugacy by their bounded Euler class. For actions of surface groups there is a weaker invariant, the Euler number which also carries some information. The prototype of the results we are intreseted in is a classical theorem by Goldman that ensures that representations into PSL(2,R) with maximal Euler number (with respect to the bound given by the Milnor-Wood inequality) are faithful and have discrete image. The same holds in the topological setting by theorems of Matsumoto, Iozzi and Burger. A representation is called geometric if it is faithful and has discrete image. Following the work of K. Mann and S. Matsumoto we will prove that the deformation space of a geometric representation is trivial meaning that it consists of a single semi-conjugacy class

Corticotropin-releasing factor receptor types 1 and 2 are differentially expressed in pre- and post-synaptic elements in the post-natal developing rat cerebellum

Corticotropin-releasing factor (CRF)-like proteins act via two G-protein-coupled receptors (CRF-R1 and CRF-R2) playing important neuromodulatory roles in stress responses and synaptic plasticity. The cerebellar expression of corticotropin-releasing factor-like ligands has been well documented, but their receptor localization has not. This is the first combination of a light microscopic and ultrastructural study to localize corticotropin-releasing factor receptors immunohistologically in the developing rat cerebellum. Both CRF-R1 and CRF-R2 were expressed in climbing fibres from early stages (post-natal day 3) to the adult, but CRF-R2 immmunoreactivity was only prominent throughout the molecular layer in the posterior cerebellar lobules. CRF-R1 immunoreactivity was concentrated in apical regions of Purkinje cell somata and later in primary dendrites exhibiting a diffuse cytoplasmic appearance. In Purkinje cells, CRF-R1 immunoreactivity was never membrane bound post-synaptically in dendritic spines while CRF-R2 immunoreactivity was found on plasmic membranes of Purkinje cells from post-natal day 15 onwards. We conclude that the localization of these receptors in cerebellar afferents implies their pre-synaptic control of the release of corticotropin-releasing factor-like ligands, impacting on the sensory information being transmitted from afferents. Furthermore, the fact that CRF-R2 is membrane bound at synapses, while CRF-R1 is not, suggests that ligands couple to CRF-R2 via synaptic transmission and to CRF-R1 via volume transmission. Finally, the distinct expression profiles of receptors along structural domains of Purkinje cells suggest that the role for these receptors is to modulate afferent inputs

The effect of detachment of cultured epithelial sheets on cellular ultrastructure and organisation

In this morphological study the (ultra)structural changes that lead to contraction of detached cultured epithelium were investigated. Keratinocytes, isolated from human skin and oral mucosa, were grown to form stratified cell sheets. The multilayers were examined with light and electron microscopy before, during and after detachment from the culture vessel. Attached epithelium had a stretched morphology with flattened cells and nuclei. Evidence is provided that after enzymatical detachment with dispase (1) basal cells became columnar by contraction of actin bundles in the basal cortex, which was accompanied by blebbing of the basal cell membrane; (2) in all cell layers cytokeratin bundles contracted resulting in displacement of desmosomes and a spherical shape of the cells and nuclei. By slow dispase-detachment at 4 degrees C or by quick mechanical detachment, shrinkage of the sheet was partly suppressed but contraction of cytokeratin and related events occurred indicating that these were the result of the spontaneous reassembly of the intermediate filament system. The results suggested that the shape and ultrastructure of all cells in an epithelial multilayer are dependent on the interaction of the basal cells with the underlying extracellular matrix