- The cyclin-dependent kinase inhibitors p19(Ink4d) and p27(Kip1) are coexpressed in select retinal cells and act cooperatively to control cell cycle exit. Cunningham, J.J., Levine, E.M., Zindy, F., Goloubeva, O., Roussel, M.F., Smeyne, R.J. Mol. Cell. Neurosci. (2002)