Abstract:
We have recently reported that the Rb protein is required for retinal progenitor cell cycle exit and rod photoreceptor development. Using Chx10–Cre;RbLox/– mice, we have generated mosaic retinae in which alternating patches of cells are lacking Rb and as a consequence lack rod photoreceptor inputs. The cells that would normally produce rods remain as immature undifferentiated cells with limited proliferation capacity (* in figure). Cones are essentially unaffected. Chx10–Cre;RbLox/– mice were used to analyse synapse formation at the OPL in the absence of rod inputs, based on the distribution of 15 immunostained synapse proteins as well as electron microscopic characterization In Chx10–Cre;RbLox/– mice we precisely identified the neurons and synapses lacking Rb by performing alkaline phosphatase EM. ERG studies are underway to characterize the functional consequences of defective synaptogenesis in the absence of Rb. Immunostaining indicates that functional synapses do not form in the absence of rod inputs in mosaic retinal patches lacking Rb. Importantly, horizontal cell processes extend apically into the deep layers of the ONL only in regions of the retina lacking Rb (figure). EM studies indicate that these are immature horizontal cells that have failed to form functional synapses. In addition, the cell autonomous role of Rb in horizontal cell development is presented based on alkaline phosphatase EM. In the absence of Rb, cells in the outer nuclear layer fail to form rod photoreceptors. These immature cells do not condense their chromatin and fail to form even rudimentary synapses with bipolar cells or horizontal cells. In the absence of these rod inputs, horizontal cells fail to properly differentiate and immature apical processes extend deep into the outer nuclear layer.
Keywords: retina: distal (photoreceptors, horizontal cells, bipolar cells)