Yolk sac erythropoiesis is impaired in Actb−/− embryos.

<p>(A) Primitive erythroid colonies (EryP) from E8.5 yolk sacs measured by methylcellulose assays show a dramatic decrease in colony forming potential in <i>Actb^−/−</i> embryos compared to <i>Actb^+/+</i> embryos. Results are given as percentage of <i>Actb^+/+</i> embryos absolute number of colonies (100%). (B) Definitive erythroid colonies (BFU-E, CFU-GM and CFU-GEMM) from E9.75 yolk sacs measured by methylcellulose assays show an 85 to 90% decrease in colony forming potential of <i>Actb^−/−</i> embryos versus <i>Actb^+/+</i> embryos. Results are given as percentage of <i>Actb^+/+</i> embryos absolute number of colonies (100%). Bars represent mean ±SEM; *P<.05, **P<.01, ***P<.001.