Cell birth and death in the mouse retinal ganglion cell layer

Here we describe quantitatively the birth and death of the two separate populations of neurons, ganglion cells and displaced amacrine cells, in the mouse retinal ganglion cell layer (GCL). The two cell types, which are roughly equally numerous, were distinguished pre- and postnatally by labeling the ganglion cells retrogradely with fluorescent dye. Embryos were labeled cumulatively with bromodeoxyuridine (BrdU) delivered by an osmotic minipump implanted in the mother; cell birth dates were established as having occurred before or after pump implantation. Early cohorts (GCL cells born before embryonic day [E] 11.8 and E12.8) were 98+/-1.1% and 99+/-0.2% ganglion cells (mean+/-SEM), respectively, and a late cohort (born after E15.8) was 97+/-1.2% displaced amacrines. Thus birth date was a strong predictor of a GCL cell's ultimate identity. Cell death in each cohort was estimated by counting cells at different time points (soon after the cohort was produced and later) and subtracting the later from the earlier number. This method avoids the problem of simultaneous birth and death that has plagued many of the earlier attempts to assess cell death. Negligible numbers died during the first week after a cell's birthday. The amount of cell death differed in the two cohorts; 48.5+/-15% and 29.0+/-12.4% in early and late, respectively, and most of it was postnatal. These findings disagree sharply with an earlier conclusion that ganglion cells die within 5 days of their birthdays or not at all.