Modified cleavage pattern after suppression of one mitotic division

Abstract

1. 1. When one nuclear division is suppressed at the 4-cell stage by UV, DNP or 4NQQ without affecting the cytoplasmic SH cycle, the treated embryo remains in the 4-cell condition while the control embryo proceeds to the 8-cell stage. Simultaneously with the fourth cleavage of the control, the treated embryo pinches off 4 micromeres directly from the larger cells. The an and Veg materials are segregated only at the time of the fifth normal division. Consequently, the time during which the An and Veg materials remain together within the same blastomere is longer than normal by the duration of two cleavage cycles (8-16-32 cell stages of control). 2. 2. When observed at the gastrula or pluteus stage, the treated embryos are quite normal. This may mean that as long as the right schedule is observed for micromere formation, delay within two cell cycles in the separation of other blastomeres does not disturb harmonious development. 3. 3. Precocious micromeres of treated embryos contain a higher concentration of RNA during the interphase, similar to normal micromeres.