Fig. 4

Expression profiling of Platynereis extracellular globins. a–h Expression patterns of Pdu-Egb-A2. The expression patterns of other extracellular P. dumerilii globins are spatially very similar and located in the same hemoglobin-producing cells of transverse trunk vessels and parapodial vessels (Additional file 10). a 18-segment juvenile show expression in transverse vessels in the trunk in a series of adjacent segments (red arrowheads). There is no expression in the rostral-most and caudal-most segments. aʹ Magnified view of three central segments. b, c 22-segment juvenile and 35-segment juvenile show expression in the parapodia (segmental appendages) for central segments and expression in lateral vessels in a few segments more rostrally and caudally located. cʹ Magnified view of a few anterior segments of worm (c) showing some residual expression in transverse vessels (red arrowheads). d Drawing of a pre-mature worm explaining the dissection and mounting of parapodia. e–g decreasing expression of Egb-A2 in parapodia of worms undergoing sexual metamorphosis. Notice the delineation of vessels by HPC in the dorsal part of parapodium (e). i Relative abundance of mRNA of P. dumerilii extracellular globin genes, detected by real-time qPCR, at different life cycle stages. The sub-adult is a 12-week old worm. Metamorphosis stage 1 is defined according to the following criteria: eyes starting to bulge, parapodia starting to transform. Metamorphosis stage 2: eyes grown to maximal volume, parapodia fully transformed, but the animal is not displaying active swimming behaviour yet. Reference genes are rps9 and sams. For stage 50 segments, stage I pre-matures, stage II pre-matures and swarming worms, the data points correspond to the median value of biological triplicates