The dnd RNA Identifies Germ Cell Origin and Migration in Olive Flounder (Paralichthys olivaceus)

Figure 4

Distribution of Podnd transcripts from 2-cell stage to 2 days after hatching. Embryos were hybridized with Podnd antisense probe. Black arrows indicate Podnd transcript aggregated regions (dark purple). Dotted straight line indicates embryonic body axis. Dotted arrows indicate PGC migration direction. (a) 2-cell stage: Podnd transcripts are concentrated at the distal edge of the 1st cleavage furrow; (b) 4-cell stage: Podnd signals are located as four spots at the distal edge of the 1st and 2nd cleavage furrows; (c) 8-cell stage: Podnd transcripts are still at the distal edge of the first two cleavage furrows; (d) 16-cell stage: Podnd transcripts are migrating from cleavage furrows to the edge of cells, respectively; (e) 32-cell stage: Podnd-positive spots are distributed into four cells, respectively; (f) morula stage: Podnd transcripts are still in four cells; ((g1) and (g2)) blastula stage: Podnd-positive cells increase and are located adjacent to each other; ((Ga) and (Gb)) magnification of the boxed region in (g1), respectively; (h) top view of early gastrula stage: Podnd-positive cells are located in the marginal region of blastoderm. Black arrowheads: (i) top view of mid gastrula stage: Podnd-positive cells are located at germ ring; ((j1) and (j2)) dorsal and lateral view of mid and late gastrula stage, respectively: Podnd-positive cells move towards the dorsal side, and some cells still lie in the germ ring region; ((j3)–(j5)) lateral view of late gastrula stage, respectively. (j3) Podnd-positive cells scattered in anterior of the trunk mesoderm appeared to align along anterior of the body axes from being randomly oriented, (j4) Podnd-positive cells moved posterior-ward, and (j5) Podnd-positive cells aligned along both sides of the body axes in posterior of the trunk region. (k) Early somite stage: Podnd-positive cells aligned along both sides of the body axes. (l) Somite stage: Podnd-positive cells moved outward and aligned as two lines along both sides of the embryonic body in the trunk region; (m) heart beating stage: the Podnd-positive cells formed clusters above the hind gut in the presumptive genital ridge; (n) hatching stage: Podnd-positive cells cluster under the genital ridge, which are above the posterior end of the hind gut and below the somites on either side of the embryonic body. ((o1) and (p)) 1-2 d after hatching: Podnd-positive cells cluster in the presumptive genital ridge region at the posterior dorsal sides of gut; (o2) longitudinal section of 1 d larva hybridized with Podnd antisense probe: Podnd-positive cells cluster in the presumptive genital ridge region at the posterior dorsal sides of gut. (o3) Cross section of 1 d larva hybridized with Podnd antisense probe: the Podnd-positive cells still aligned at the genital ridge which was at the dorsal sides of the hind gut, ventral side of notochord. Scale bar: 100 µm.