Germline cyst formation and incomplete cytokinesis during Drosophila melanogaster oogenesis.

Germline cyst formation via incomplete cytokinesis (IC) is necessary to generate functional eggs and sperm in various organisms. Drosophila melanogaster oogenesis is an ideal system for studying IC. 29 stages of germline cyst formation can be identified in D. melanogaster oogenesis. We have defined necessary terminology to describe IC and have developed a method to measure the sizes of contractile rings and ring canals. Time course study of germline cyst formation demonstrates that contractile ring constriction proceeds to a defined end point unique for each mitotic division. Contractile rings constrict to a greater degree, resulting in smaller ring diameters, for each subsequent round of mitotic division. Contrary to conventional wisdom, ring canal growth is not initiated until well after the fourth mitotic division. Ring canals grow, in an orderly manner, with ring canals derived from the first mitotic division enlarging first followed by those from the second, then those from the third, and finally those from the fourth mitotic division. This work establishes a foundation for identifying genes specific for IC and for elucidating the molecular mechanism underlying this aspect of germline cyst formation.