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The specification of metameric order in the insect callosobruchus maculatus coleoptera 2. the effects of temporary constriction on segment number


, : The specification of metameric order in the insect callosobruchus maculatus coleoptera 2. the effects of temporary constriction on segment number. Wilhelm Roux's Archives of Developmental Biology 193(5): 326-338

Mechanically dividing an insect egg into anterior and posterior fragments results in a segment gap (Sander 1976), a loss of non-terminal segments in the constricted region. By altering the stage and duration of constriction, different types of egg fragments were produced in the pea beetle Callosobruchus. The patterns formed by these fragments suggest the existence of interactions between anterior and posterior egg regions that influence segment patterning and placement. Segments in excess of the numbers expected on the basis of permanent constrictions were produced in fragments when the constriction was released before cellularization occurred and the complementary fragment degenerated. Apparently, the degenerating fragment induced the formation of excess segments in the developing fragment. Differences in the time and extent of excess segment formation in anterior vs. posterior fragments suggest an asymmetric distribution of prerequisites for segment formation. This conclusion is consistent with the finding that a partial reversal of segment sequence (double abdomen formation) can be induced only in posterior fragments by a degenerating fragment, but not in anterior fragments. The formation of excess segments shows that the segment gap observed after permanent separation cannot be due to non-specific damage, caused by the process of constriction as such, to the egg or to localized putative segment precursors.

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