Fig. 2. The level of CTD phosphorylation is altered in pole cells of bcd-nos3'UTR embryos. Co-immunostaining of embryos with monoclonal antibody H5 (green) and anti-Vasa antiserum (red). The H5 antibody specifically recognizes RNA polymerase II CTD repeats phosphorylated on serine 2. (A) Wild-type embryo. H5 antibody staining is readily apparent in the transcriptionally active somatic nuclei but not in the transcriptionally quiescent pole cells. (B) bcd-nos3'UTR embryo. H5 antibody stains pole cell nuclei in addition to the adjacent somatic nuclei, indicating that the level of CTD phosphorylation is elevated in these pole cells. (C) pgc embryo. H5 antibody stains pole cell nuclei in early blastoderm embryos. Note that all the somatic nuclei have not yet reached the periphery.