Sphk2 deficiency results in inefficient PP fragmentation in vivo. (A) Role for Sphk2 in PP shedding in vivo visualized by MP-IVM. WT MKs frequently shed PPs as shown in the first and fourth rows from top to bottom. Loss of Sphk2 abolishes PP shedding as shown in the second, third, and fifth rows from top to bottom. Images were captured through a ×20 water immersion objective lens with NA = 0.95 using a LaVision BioTech TriM Scope system. Arrowheads and arrows indicate the tips of PPs. Green, MKs and PP; red, sinusoids. All scale bars represent 20 µm; time in minutes. The dashed line highlights the sinusoids. (B) Percentage of PP fragmentation events observed by MP-IVM over 1 hour in WT × CD41-YFP^ki/+ or Sphk2^−/− × CD41-YFP^ki/+ naïve (nontransplanted) mice. Data are pooled from 3 to 5 independent experiments from each group (n = 21-43 per group). (C) Percentage of PP fragmentation events observed by MP-IVM over 1 hour in WT × CD41-YFP^ki/+ or Sphk2^−/− × CD41-YFP^ki/+ chimeras. Data are pooled from 3 to 4 independent experiments from each group (n = 21-31 per group). (D) MPV in peripheral blood from WT and Sphk2^−/− mice on a Balb/c background (n = 9 for WT; n = 6 for Sphk2^−/− mice). All error bars represent SEM.