Syk^{R41Afl/fl;PF4-Cre} mouse development. (A) Syk^R41Afl/fl targeted locus. Following crossbreeding with PF4-Cre–expressing mice, the loxP flanked DNA is excised, allowing for expression of the knockin mutation. (B) Expression of Syk was measured by western blotting platelet whole-cell lysates (n = 3) (i). Platelet count and size (n > 10, ***P < .005) (ii). Surface expression of stated glycoproteins was measured on platelets by flow cytometry (n = 3) (iii). Platelet count and size for Syk radiation chimeras (n = 3) (iv). (C) Blood-lymphatic mixing is visible in the skin of embryonic day 14.5 embryos (i) and in the mesenteric vessels of adult mice (ii). For clarity, colored lines are traced below (red, arteriole; blue, venule; green, lymphatic). Chyle can be seen in the serosa of recently weaned R41A mice (iii). Connections between the lymphatic and vein were directly observed by intravital microscopy. The dotted box exemplifies the area near the serosa where the branching vessels are densely packed, and the dashed white lines are highlighting the vessel edges (iv). R41A, Syk^{R41Afl/fl;PF4-Cre}; WB, western blot.