Cellular Expression of Connexin45 in the Mouse Retina

Abstract

Abstract: : Purpose: To identify the cellular expression of the gap junction channel forming protein connexin45 (Cx45) in the mouse retina. Methods: Transgenic mice were generated that express the lacZ reporter gene under the control of the Cx45 promotor. Retinal neurons were identified with established retinal markers in vertical sections and dissociated cells, and by intracellular injection of Neurobiotin in wholemount preparations. Cx45 was then localized by targeting lacZ expression to the appropriate cell types. In addition, single cell RT-PCR was performed with cytoplasm harvested from horizontal, bipolar and ganglion cells. Results: Cx45 is expressed in a subpopulation of ON cone bipolar cells identified by the length of their axons, but not in rod bipolar cells identified by the presence of PKC immunoreactivity. These results were confirmed by single cell RT-PCR of bipolar cells using corresponding primers. Horizontal cells do not express Cx45. Neurobiotin-labeled ganglion cells were classified according to the shape and size of their soma and the ramification pattern of their dendrites. Cx45 was expressed in bistratified ganglion cells with dendritic field diameters between 150 - 250 µm. The two levels of stratification corresponded with the ON- and OFF sublaminae, respectively. Spiny and recursive dendrites of all orders were of uniform thin diameter. In many instances, tracer coupling to other ganglion cells was observed. Based on more detailed morphological characteristics, these bistratified ganglion cells can be subdivided into two subpopulations, one having all the features attributed to direction-selective ganglion cells. Cx45 expression was never co-localized with monostratified alpha ganglion cells exhibiting strong tracer coupling, an observation which was supported by single cell RT-PCR data. Conclusions: We have shown that Cx45 is expressed in a subpopulation of cone bipolar cells and in bistratified ganglion cells which show homologous tracer coupling and share many similarities with direction selective ganglion cells.

Keywords: gap junctions/coupling • retina: proximal(bipolar, amacrine, and gangli • retinal connections, networks, circuitry