Fig. 6

Animal view of the cleavages of micromere 4d in M. crozieri. a–e The cleavage pattern of micromere 4d (marked in red) is visualized using a 3D viewer (Fiji), showing in grey the position of all remaining nuclei except 4A-D and 4a–4c. a Micromere 4d before its division. b Micromere 4d divides along the animal–vegetal pole and daughter cell 4d² is budded into the interior of the embryo and in close proximity to micromeres of the animal pole. c–e Both daughter cells of micromere 4d divide again, but this time both cells cleave meridionally. f Micromere 4d undergoes mitosis revealing the D quadrant. g The asymmetric division of micromere 4d along the animal–vegetal pole is barely visible but causes blebbing (arrow pointing at dashed line). h After the division, daughter cell 4d¹ remains large and is more vegetally positioned and therefore readily visible. 4d² is budded into the interior of the embryo, more animally positioned and cannot be seen anymore without optical sectioning. i, j Bilateral symmetry is clearly visible after the division of 4d¹. Oocytes were microinjected with nuclear marker H2A-mCherry (red) and microtubule marker EMTB-3xGFP (green) and the embryo used for 4d microscopy with OpenSPIM (A-E) or under a Zeiss Axio Zoom.V16 Stereo Microscope (F-J); hpo = hours post oviposition. Scalebar in images captured with the Axio Zoom = 100 µm