Mitotic waves and embryonic pattern formation: No correlation inCallosobruchus (Coleoptera)

In early insect embryogenesis, mitosis (which is not accompanied by cell division) often starts at one or both egg poles and spreads like a wave over the egg. Relationships between these waves and those processes which coordinate spatial cell differentiation have been proposed. One possibility is that the egg region which has a slower mitotic rate may become temporally advanced in differentiation because of its longer interphase periods, so that the egg becomes polarized (Agrell 1962). Alternatively, the mitotic waves might reflect the position of different determined states (Kauffman 1973). We investigated the mitotic waves inCallosobruchus eggs, treated to produce 20% partially reversed segment sequences (double abdomens). In normal eggs, mitotic waves move predominantly from anterior to posterior whereas in treated eggs, the reversed posterior to anterior orientation was predominant. Despite this, we concluded that mitotic waves do not reflect processes involved in the specification of segment position because the reversal of mitotic waves was more than twice as frequent as the reversal of segment sequence and because they occurred in various control experiments in which there was no reversal of segment sequence.