In the process of segmentation, deep ventral-lateral grooves form, corresponding to the incipient segmental boundaries. The interior aspects of these segmental boundaries are the sites for future muscle attachment. Another process that takes place progressively during germ band retraction is known as dorsal closure . It takes about two hours, beginning 11 hours after the start of development. Dorsal closure is the process whereby the stretched amnioserosa is covered by epidermal cells that will ultimately fuse at the dorsal midline.
Genes involved in dorsal closure include rho , hemipterous and basket .
With its part in development played, the enclosed amnioserosa is then absorbed by the yolk. Consequently it is argued that peb expression in the amnioserosa is crucial for germ-band retraction. Since Pebbled is expressed in the midgut , it became important to show whether this expression is important in driving germ band retraction. The embryonic midgut can be eliminated without affecting germ-band retraction. However, elimination of the amnioserosa results in the failure of germ-band retraction, implicating amnioserosal expression of Pebbled as crucial to this process.