Bpvas and Bpnos expression in Brachionus embryos. (A-J) Expression of Bpvas RNA in Brachionus embryos. Scale bars are 100 μm. Where known, anterior is at the top. (A) Bpvas RNA is first seen ubiquitously in the just-laid egg and continues to be expressed in all cells through eight (B) and 16 (C) cell stages up to stages where we can count at least 96 cells (D and E). At stages later than that, Bpvas expression is lost from most cells (F) and focuses to a small number of cells (G and H), which become partitioned into the posterior of the embryo into a dumbbell-shaped domain just anterior to the tail, which we interpret as the developing ovary. (K-N) Expression of Bpnos RNA. All scale bars are 100 μm, where known anterior is to the top. (K) Expression of Bpnos RNA in a one-cell embryo; RNA is ubiquitous throughout the embryo. This RNA is substantially reduced in two-cell embryos (L) and is absent by the 16-cell stage (M) throughout the rest of development until embryos are just about to hatch (N) when expression appears in a similar dumbbell-shaped domain as emerges for Bpvas expression.