R4 [FBbt_00004219]

R4

ID: FBbt_00004219

Outer photoreceptor cell of the adult eye whose rhabdomere is located in the middle of the longer of the two non-parallel sides of trapezoid of rhabdomeres in each ommatidium, in between the rhabdomeres of R3 and R5. It has a single axon that projects along a single lamina optic cartridge (Fischbach and Dittrich, 1989; Wolff and Ready, 1993).

The name photoreceptor cell R4 is occasionally, mistakenly assumed to refer to any Rh4 expressing photoreceptor cell. This is incorrect. This term only refers to a type of adult eye photoreceptor cell. The name is based simply on the position of the cell and its rhabdomere within each ommatidium - see figure 4 in Wolff and Ready, 1993. Cell connectivity was determined by analysis of semi-automated EM reconstruction of 749 serial sections of 21 complete lamina cartridges. The number of synaptic connections for R4 (presynaptic/postsynaptic) in a single lamina cartridge with each cell type was the following: L1 (38/-), L2 (41/-), L3 (8/-), L4 (-/1), Lai (37/2), T1 (2/-) and epithelial glia (9/-) (Rivera-Alba et al., 2011).