Describe the first interaction that must occur between the R7 precursor cell and the R8 cell for the R7 precursor to differentiate to an R7 photoreceptor cell.

the eye contains 800 photoreceptor sensory units called ommatidia, these contain 22 cells, 8 of which are photosensitive and have been called R cells, currently 8 types have been described that are listed from 1 to 8 with the letter R, during the development of the ommatidia is expressed by the B088 proteins and through a reaction with the RTKs ligand of R8 induction occurs to the formation of the R7 precursor