A morphological and developmental study of Drosophila embryos ligated during nuclear multiplication

In the Drosophila embryo, determination is established at the cellular blastoderm and a mosaic type development is observed after this time. Before the blastoderm stage, however, development is not of the mosaic type, as ligation during the nuclear multiplication stage causes a change in the spatial organization of the larval pattern. An aberration in determination leads to an increase in segment size, an increase in the number of cells per segment, and a decrease in segment number. This abnormal determination of blastoderm cells has also been demonstrated experimentally by marking corresponding regions of the blastoderm in ligated (posterior fragments only) and nonligated embryos. When the blastoderms of nonligated and ligated embryos are punctured at the same site, ligated embryos produce larvae with damage in segments posterior to the segments damaged in larvae from nonligated embryos. Ultrastructurally, no abnormalities were observed in the plasma membrane at the time of ligation or later in blastoderm cells which formed in the ligation area of these embryos. Evidence from this study, as well as other sources, indicates that determination of segmentation is under maternal control.