Figure 1From: Trans-generational epigenetic regulation of C. elegans primordial germ cellsUnique and dynamic regulation of Pol II in the embryonic germline. (A) Transcription status and histone modification dynamics in C. elegans early embryonic blastomeres. The asymmetric divisions of P-lineage cells (P0 to P3) produce both germline and somatic blastomeres. The last P cell division (P4) is symmetric and produces two germline-committed primordial germ cells (PGCs), Z2 and Z3 and these cells arrest at G2 phase through the rest of embryogenesis [68]. Two maternally expressed CCCH zinc finger proteins, OMA-1/2 and PIE-1, act sequentially in P0 to P4 to maintain transcriptional quiescence independently of the chromatin environment [14, 69, 70] (orange line). At the P4 division, PIE-1 is degraded quickly and 'active Pol II' (H5 staining; magenta line) appears in the PGCs (circled by blue dotted line). H3K36me3 (black) and H3K4me2 (green) are initially present in both the transcriptionally quiescent P-lineage and their somatic sisters, where transcription is activated. MES-4, which is essential for germ cell viability, produces H3K36me in the germline precursors independently of transcription [21]. H3K4me2 is also maintained through the P-lineage by an unidentified mechanism, but the level of H3K4me2 becomes almost undetectable in the PGCs [15] (indicated by dotted green lines). (B-L) H5 staining of Pol II Ser2P in the PGCs of (B-E) wild type, (F-I) mes-4 and (J-L) mes-2during embryogenesis; (B,F)~150 minutes post-fertilization at 22°C, ~26-cell stage; (C,G,J) ~200 minutes, ~90-cell stage; (D,H,K) ~450 minutes, ~1.5-fold stage; (E,I,L) >500 minutes, 2- to 3-fold stages. PGCs are boxed and shown by arrows. DAPI staining, red; H5 antibody staining, green; PGL-1 (germline marker) staining, blue. In the lower panels, PGCs are enlarged, and the separated channels for DAPI and H5 staining are shown in grayscale. Scale bars: 10 μm.Back to article page