Amacrine cell genesis is elevated postnatally in Zac1+m/- retinae. (a-d) E18.5→4DIV wild-type (a,a',c,c') and Zac1+m/- (b,b',d,d') explants co-labeled with BrdU (red, S-phase) and Pax6 (green; amacrine cells (a,a',b,b') or Math3 (green; amacrine and bipolar precursors in INL (c,c',d,d'). (e,f) E18.5→4DIV explants labeled with Pax6 alone (red). (g,g',h,h') Birthdating of E18.5→8DIV wild-type (g,g') and Zac1+m/- (h,h') retinal explants exposed to BrdU (green) at 2DIV and co-labeled with anti-Pax6 (red). BrdU/Pax6 double+ cells are marked by arrowheads in (g',h'), which are high magnification images of boxed areas in (g,h), respectively. (i) Percentage of BrdU/Pax6 double+ nuclei (amacrine cells born at time of BrdU exposure) in wild-type (black bar; BrdU at 1DIV: 562 BrdU/Pax6 double+/2,385 Pax6+; 2DIV: 527 BrdU/Pax6 double+/6,022 Pax6+; 4DIV: 77 BrdU/Pax6 double+/1,496 Pax6+; all counts in 8DIV explants) and Zac1+m/- explants without an ECL (grey bar; BrdU at 1DIV: 1,307 BrdU/Pax6 double+/4,084 Pax6+; 2DIV: 527 BrdU/Pax6 double+/4,926 Pax6+; 4DIV: 75 BrdU/Pax6 double+/1,660 Pax6+) and Zac1+m/-+ECL explants (white bar; BrdU at 1DIV: 2,126 BrdU/Pax6 double+/6,107 Pax6+; 2DIV: 883 BrdU/Pax6 double+/4,386 Pax6+; 4DIV: 335 BrdU/Pax6 double+/3,587 Pax6+). (j) Model of amacrine cell genesis in wild-type (red line) versus Zac1+m/-+ECL (blue line) retinae.