Question

In Drosophila, the transition from the syncytial blastoderm stage to the cellular blastoderm stage is a dramatic change that necessitates very different mechanisms to pattern the embryo. We'll talk more about his next week.

To get started thinking about this, briefly describe the syncytial and cellular blastoderm embryos, and point out the major difference in cellular organization between these embryonic stages.

Answer 1

In Drosophila development, insect eggs undergo superficial cleavage. In this process, zygote undergoes after 8 nuclear mitotic divisions, 256 nuclei are produced. During 9^th cycle, 5 nuclei reach the surface of the posterior pole in the embryo, they become enclosed by cell membrane and generate pole cells (that form gametes). Most of the other nuclei reach the periphery of the embryo and undergo more mitotic divisions.

Syncytial blastoderm is that stage in Drosophila embryo development where the cleavage nuclei is present in cytoplasm. The multiple nuclei are not separated by membrane. Karyokinesis has occurred but no cytokinesis. Only membrane exist is that of egg itself.

During 10^th cleavage cycle each nucleus is surrounded by cytoskeletal elements (microfilaments and microtubules). After 13^th division cycle, the egg membrane folds inwards between the nuclei to form separating individual cells from inner yolk cytoplasm. This process creates cellular blastoderm