Figure 5.

Long-term treatment of Platynereis with synthetic MIP enhances growth and decreases time to cephalic metamorphosis. (A-D) SEM images depicting posterior segment addition followed by cephalic metamorphosis in Platynereis dumerilii, dorsal views. White arrowhead indicates parapodia of the 1^st chaetigerous segment, which are transformed into the posterior tentacular cirri of the head during cephalic metamorphosis. (A) 6 dpf 3-segmented nectochaete larva. (B) 4-segmented errant juvenile. (C) 5-segmented errant juvenile. Cephalic metamorphosis has begun. (D) Cephalic metamorphosis is complete. (E) Schematic of the Platynereis MIP precursor protein. The N-terminal signal peptide (teal) and the predicted peptides (grey) flanked by basic cleavage sites (red) are shown. The predicted mature MIP peptide sequences are indicated below. (F) Percentage of 25 dpf Platynereis larvae/juveniles with 3, 4, 5 segments, or complete cephalic metamorphosis following exposure to 5 μM synthetic MIP peptides, from 4 dpf onwards. Data are shown as mean +/- s.e.m, n = 3 x 30 larvae. NSW, natural seawater control. (G) Total length of 25 dpf Platynereis larvae/juveniles exposed to 5 μM synthetic MIP peptides, from 4 dpf onwards. Data are shown as mean +/- 95% confidence interval, n = 90 larvae. (F, G) p-value cut-offs based on unpaired t-test: *** <0.001; ** < 0.01; * <0.05. (H) Differential interference contrast light micrographs of example control and MIP7-treated individuals at 1 month post fertilization. Scale bars: 100 μM. Abbreviations: ac, anal cirrus; adc, anterior dorsal cirrus; ant, antenna; avc, anterior ventral cirrus; ch, chaetae; pdc, posterior dorsal cirrus; pp, parapodia; pro, proctodeum; pt, prototroch; tt, telotroch; 4CS, 4^th chaetigerous segment; 5CS, 5^th chaetigerous segment; 4CS’, 4^th chaetigerous segment after cephalic metamorphosis; 5CS’, 5^th chaetigerous segment after cephalic metamorphosis.