Figure 6
Decreased follistatin expression coincides with the generation of horizontal cells. (A-B): Follistatin (solid line) and follistatin-like 1 (FSTL1, dashed line) mRNA levels during retinal development relative the lowest value respectively which is set to 1 (follistatin: 1 = st28; FSTL1: 1 = st42). The X-axis denotes the embryonic stages analysed and the Y-axis denotes the relative mRNA levels in log scale (A) or linear scale (B). Numbers in parenthesis in B denote the relative follistatin mRNA level-value at st18 and 38, respectively. (C-D): Follistatin immunoreactivity (red) in the developing retina at st22 (C) and st25 (D) reveal a central-to-peripheral gradient of follistatin expression. Highest levels are expressed peripherally and sharp boundaries between high and low expression are evident (black arrows). The onset of Lim1 expression (green) is trailing the wave-front of decreasing follistatin expression. (E): 22 h after follistatin treatment at st21, st22 or st23, the number of Lim1+ cells decreases by approximately 20–25%. Lim1+ cells were counted in 20× visual fields and expressed as Lim1+ cells/mm2 retina. Blue squares indicate the means of individual control treated animals and red circles indicate the means of individual follistatin-treated animals. The medians are indicated by a black line, * denote significant differences (p < 0.05, Mann-Whitney test). F-G: Lim1 expression (green) in central retina 22 h after control (F) or follistatin (G) treatment in st22 embryos. Scale bars are 100 μm (C-D), and 20 μm in G (valid for F-G).