Venous thrombosis with fibrinogen AαE or Aα expression in MO-induced fibrinogen knockdowns, monitored in early zebrafish larvae with fluorescent erythrocytes. (A) One- to 2-cell embryos from a Tg(gata1:DsRed) × TU mating were microinjected with an MO that inhibits fga mRNA by antisense targeting of the exon 1–intron 1 splicing boundary, lowering by over 90% the expression of fibrinogen Aα or AαE. This was done in the presence or absence of Aα-chain or AαE cDNA expression, which cannot be targeted by the MO, and the TTO assessed at 3 dpf after laser injury in the PCV. Measurements were made by monitoring the red fluorescent erythrocytes in these larvae, a single frame image of which is given to the right. The dorsal aorta (DA), PCV, and laser-injury (LI) position are labeled. Scale bar, 50 μm. (B) The TTO results for the respective conditions with the number of embryos assessed below each in brackets, and P values of a Mann-Whitney U test between certain groups. Each circle represents an individual larva. (C) The gata1:DsRed-associated fluorescence accumulation in the first 24 seconds postlaser injury are plotted, for each group of larvae from within a defined region around the laser-injury site. Average fluorescence over time is plotted with error bars representing the standard error of the mean for each grouping. The number of larvae per group is shown in brackets next to the group color indicators. (D) The data for individual larvae 20 seconds postlaser are plotted for each group, with the mean and standard deviation. P values are indicated for unpaired Student t tests; results of further tests at 16, 20, and 24 seconds postlaser are given in supplemental Tables 1-3.