| Effect of inhibiting the release of the first polar body (PB1) with cytochalasin B on meiotic division of fertilized eggs and ploidy composition of 4-8 cell embryos was studied in the zhikong scallop, Chlamys ferreri. The development of induced embryo and early larvae was demonstrated. The mechanism of tetraploids formation was revealed, providing useful reference for optimizing tetraploid production technique. Fluorescent staining method for eggs of marine bivalves was established using FITC-anti-α-tubulin and propidium iodide (PI) for observation of spindles and chromosomes, respectively. Several types of meiotic apparatuses and corresponding chromosome segregation including bipolar (18.9%), tripolar (38.9%), double bipolar (16.5%), unsynchronized (2.9%) and unclassified pattern (23.0%) were observed during meiosis II in CB treated eggs. It indicated that bipolar segregation and double bipolar segregation resulted in the formation of triploids and tetraploids respectively while other kinds of segregation would mainly lead to the occurrence of aneuploids. The observation of embryo and early larvae in treated and controlled group through optical microscopy and electron microscopy indicated a remarkably higher proportion of malformed embryos in gastrulae stage. The arrested gastrulae and trochophore were found significantly higher in treated groups than that in controls during 48h post-fertilization. It indicated that it was gastrulae stage when induced larvae were arrested at an appreciate proportion. This research showed that inhibition of PB1 remarkably changed the second meiotic division, including the dynamics of spindle organization and chromosome segregation, resulting in the formation of embryos with variable ploidy composition. However, the large proportion of arrested gastrulae remains a major challenge for tetraploid production. |
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