Figure 5.

Summary of localizations of cell cycle regulators and markers during P3 and P4 in the O. dioica coenocyst, with respect to organizing centers (OC), meiotic nuclei in prophase I, and endocycling nurse nuclei. In P4, a proportion of the meiotic nuclei had been selected to populate growing oocytes (black bars), whereas the remaining meiotic nuclei had not been selected (red bars) and were present in the general coenocyst cytoplasm. The degree of presence of each parameter is indicated by degree of shading of the lines from light (weakly present) to dark (strongly present). M-phase MPM-2 phosphoepitopes were observed on OCs throughout P3 and P4, as was pERK. Cell cycle regulators odCDK1a,d,e, phospho-Plk1 (pPLK1) and phospho-Aurora (pAurora) were present on OCs during P3 but lost from OCs during P4. Toward the transition from P3 to P4 H3-pS28 staining increased on meiotic nuclei. This staining was retained throughout P4 on selected meiotic nuclei but was progressively lost on non-selected meiotic nuclei. At P4, odCDK1 paralogs translocated from OCs to non-selected meiotic nuclei whereas pPlk1, translocated from OCs to selected meiotic nuclei. The pAurora kinase, present on all meiotic nuclei in P3, was retained on selected nuclei in P4 but lost from non-selected meiotic nuclei. MPM-2 phosphoepitopes, absent from meiotic nuclei in P3, became progressively enriched on both selected and non-selected meiotic nuclei during P4. MPM-2 phophoepitopes also appeared as small foci within nurse nuclei during P4, as did foci of pERK, the latter consistent with observations in previous work.²⁸ Nurse nuclei also exhibited nucleolar pPlk1 staining during P4. In P3, odLamin1 surrounded both meiotic and nurse nuclei. During P4, odLamin was retained on nurse and selected meiotic nuclei but was lost from non-selected meiotic nuclei.