Fig. 7
Blebbing events during meiosis and spiral cleavage in the polyclad flatworm M. crozieri. a–d Blebbing during egg maturation in M. crozieri oocytes. a Extrusion of first polar body (white arrow) and depression of the oocyte at the animal pole (black arrowhead). b Oocyte with one polar body and darkish pigment accumulated at the animal pole. c Cell blebbing is recognizable by the formation of amoeboid/pseudopodia-like irregularities all over the cell membrane. d An egg cell is shown with two polar bodies and darkish pigment accumulated at the animal pole. e–l Blebbing is depicted during the third and fourth quartet formation. e–h Peculiar protrusions, which appear prior to third quartet formation (16–32-cell stage) among all four macromeres are shown. i, j Vegetal (i) and lateral view (j) of the division of macromere 3D into tiny macromere 4D (white arrowhead). k, l Blebbing is accompanied by severe deformations of large micromeres 4b and 4d. m–p Animal view of the cleavages of micromere 4d in M. crozieri. m Chromosome condensations are only visible in 4d. n Division of 4d is visible along the animal–vegetal axis of the embryo. White arrowheads show cytoplasmic perturbations during the cleavage of micromere 4d. o The meridional division of 4d1 takes place. p The next division of the daughter cells of 4d1 is depicted. m′–p′ The 4d cell and its progenies have been depicted separately below at increased exposure levels. Embryos with fluorescent signal were microinjected as oocytes with a microtubule marker (EMTB-3xGFP) and a histone nuclear marker (H2A-mCh). Live imaging was performed under a Leica DMI3000 B inverted scope (a–g), a Zeiss Axio Zoom.V16 Stereo Microscope (h–l) and an OpenSPIM (m–p). Scalebar is 100 µm in a and h, 50 µm in I-L, 100 µm in a and e and 50 µm in m–p