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Muller cells are the dominant macroglial cells in the retina of all vertebrates. They fulfill a variety of functions important for retinal physiology, among them spatial buffering of K+ ions and uptake of glutamate and other neurotransmitters. To this end, Muller cells express inwardly rectifying K+ channels and electrogenic glutamate transporters. Moreover, a lot of voltage- and ligand-gated ion channels, aquaporin water channels, and electrogenic transporters are expressed in Muller cells, some of them in a species-specific manner. For example, voltage-dependent Na+ channels are found exclusively in some but not all mammalian species. Whereas a lot of data exist from amphibians and mammals, the results from other vertebrates are sparse. It is the aim of this review to present a survey on Muller cell electrophysiology covering all classes of vertebrates. The focus is on functional studies, mainly performed using the whole-cell patch-clamp technique. However, data about the expression of membrane channels and transporters from immunohistochemistry are also included. Possible functional roles of membrane channels and transporters are discussed. Obviously, electrophysiological properties involved in the main functions of Muller cells developed early in vertebrate evolution. GLIA 2017;65:533-568.

The transcription factor Tieg1/Klf10 belongs to a family of Sp1/Klf proteins that have been shown to play important roles during development and maintenance of various tissues and cell types. Upregulation of Tieg1/Klf10 has been reported for TGF-beta, BMP2, BMP4, ActivinA and GDNF as members of the TGF-beta superfamily. Moreover, estrogen, the cytostatic drugs homoharringtonine and velcade as well as nitric oxide are also able to trigger Tieg1/Klf10 transcription. Recent studies suggest a role for members of the neurotrophin family in regulating Tieg1/Klf10 transcriptional upregulation. Using semi-quantitative RT-PCR and immunoblotting, we present data describing that nerve growth factor (NGF) regulates the expression of Tieg1/Klf10 in the pheochromocytoma cell line PC12 in a TrkA-dependent manner. Moreover, we provide evidence for the existence of NGF-responsive elements in the 5'-regulatory region of Tieg1/Klf10 that contain binding sites for the transcription factors Sp1 and CREB. After treatment with NGF PC12 cells exit the cell cycle and start to differentiate towards a neuron-like phenotype indicated by neurite outgrowth. Using flow cytometry and differentiation assays we demonstrate that Tieg1/Klf10 reduces cell cycle progression in PC12 cells but fails to promote their terminal differentiation. Together, our results identify Tieg1/Klf10 as a new NGF target gene and substantiate its anti-proliferative function in the NGF signaling pathway in PC12 cells.

Publisher Summary This chapter reviews that cytoarchitectonics is commonly used as a descriptor of tissue architectonics. To construct stereotaxic atlases of the central nervous system (CNS), cytoarchitectonics is focused on neurons and distribution patterns of their cell bodies. The chapter discusses that the unique complexity of cellular interactions in CNS tissue is based on the intra-epithelial association of cells, and confrontation of multiple cell types of different origin and contact relations with neurons and/or intracerebral (intra-epithelial) blood vessels. To assess the interactive potential of non-neuronal cell types, their ramified shapes have to be characterized in terms of topography of structural and molecular cell components, and their contact relations within metacellular entities and tissue compartments. The chapter reviews that by utilizing structural, morphogenetic, and topographical information including quantitative data, cell-type specific cytoarchitectonics turns out to be a valuable tool that combines tissue-related cell structures with cell-related tissue compartments. This approach is exemplified by endothelia of intracerebral blood capillaries, microglia, oligodendroglia, and ependymo-astroglia with special reference to astrocytes.