Zebrafish facial lymphatics develop through sequential addition of venous and non-venous progenitors (2019)
Figure 4

Figure 4. Vegfr3 signalling is not required for facial lymphatic progenitor formation

(A-H) Lateral images of the PHS fixed at 36 hpf (A-B, E-F) and 42 hpf (C-D, G-H) in lyve1b:EGFP fish that have been fluorescently immunostained with anti-PROX1 (green) and anti-GFP (red). These show a decrease in the number of Prox1-positive PHS ECs in the ccbe1 morpholino-injected (B, D) and sFLT4 mRNA-injected embryos (F, H) compared with control morpholino-injected (A, C) and uninjected embryos (E, G). At 42 hpf, ccbe1 morpholino-injected embryos (D) and sFLT4 mRNA-injected embryos (H) lack the PHS-LP domains present in the control embryos (C, G; large arrow heads).

(I-J) Quantitation of the percentage of PHS ECs that are lymphatic progenitors relative to the total number of PHS ECs in control morpholino-injected embryos at 36 hpf (n = 27) and 42 hpf (n = 17) and ccbe1 morpholino-injected embryos at 36 hpf (n = 36) and 42 hpf (n = 12) (I) or in uninjected embryos at 36 hpf (n = 27) and 42 hpf (n = 21) and sFLT4 mRNA-injected embryos at 36 hpf (n = 26) and 42 hpf (n = 17) (J).

(K) Quantitation of the total number of PHS ECs in control morpholino-injected embryos at 36 hpf (n = 27) and 42 hpf (n = 17) and ccbe1 morpholino-injected embryos at 36 hpf (n = 36) and 42 hpf (n = 12) or in uninjected embryos at 36 hpf (n = 27) and 42 hpf (n = 21) and sFLT4 mRNA-injected embryos at 36 hpf (n = 26) and 42 hpf (n = 17).

(L-O) Lateral images of the FLS (L, N; dotted line) or dorsolateral CCV region from where the FLS normally sprouts (M, O; dotted line) fixed at 36 hpf in lyve1b:EGFP embryos that have been fluorescently immunostained with anti-PROX1 (green) and anti-GFP (red). These show no change in the number of Prox1-positive lymphatic progenitors in the ccbe1 morpholino-injected (M) and sFLT4 mRNA-injected (O) embryos compared with control morpholino-injected (L) and uninjected (N) embryos.

(P) Quantitation of the percentage of dorsolateral CCV ECs that are lymphatic progenitors relative to the total number of dorsolateral CCV ECs in control morpholino-injected (n = 26), ccbe1 morpholino-injected (n = 27), uninjected (n = 28) and sFLT4 mRNA-injected embryos (n = 32).

(Q) Quantitation of the total number of dorsolateral region CCV ECs in 36 hpf embryos that were uninjected or injected with control morpholino (n = 26), ccbe1 morpholino (n = 27), or sFLT4 mRNA (n = 32).

(R-U) Dorsolateral images of the VA-L fixed at 54 hpf in lyve1b:EGFP larva that have been fluorescently immunostained with anti-PROX1 (green) and anti-GFP (red). These show that lymphatic progenitor formation still occurs within the VA-L in ccbe1 morpholino-injected (S) and sFLT4 mRNA-injected embryos (U), with Prox1 expression resembling that of controls (R, T).

Data information: Error bars represent standard deviation; **** P < 0.0001, *** P < 0.001, ns = non-significant by one-way ANOVA. CCV = common cardinal vein, EC = endothelial cell, FLS = facial lymphatic sprout, hpf = hours post fertilisation, PHS = primary head sinus, PHS-LP = primary head sinus-derived lymphatic progenitor, VA-L = ventral aorta lymphangioblast. Scale bar = 50 µm