Shedding and debris collection must be precisely synchronized to maintain proper rod and cone cell function. How this synchronous cycle of uptake and digestion is maintained is not completely clear. Nandrot and colleagues now show that, in mice lacking the integrin, the normal burst of uptake activity at first light was completely missing and instead uptake occurred steadily throughout the day. Debris accumulated inside the cell and was not destroyed.
That epithelial cells could still take up debris at all was a surprise, as tissue culture experiments showed that cells missing this integrin were unable to pick up rod cell fragments. The link to digestion was also surprising because integrin signaling has never been linked to cellular digestion functions. Perhaps the same signal triggers a cascade that initiates both concerted uptake and digestion. The authors are now trying to identify the protein that binds to the integrin and triggers these functions.