Germ Band Extension in Drosophila String Mutants

Date of Award

Spring 6-8-2023

Document Type

Undergraduate Thesis

Degree Name

Bachelor of Science in Molecular Biology

Organizational Unit

College of Natural Science and Mathematics, Biological Sciences

First Advisor

Dinah Loerke

Second Advisor

James Todd Blankenship


Germ band extension, Drosophila, Developmental biology, Fast phase, String, T1 transitions


In Drosophila germ band extension, cell intercalation is achieved by contraction of vertical interfaces (between anterior-posterior neighboring cells), and elongation of horizontal interfaces (between two dorsal-ventral neighboring cells). The symmetry-breaking behavior results from a system of planar polarity, which is created by anisotropic distribution of certain proteins at cell-cell interfaces – Myosin II at vertical and Bazooka at horizontal interfaces. The cell-cell interfaces systematically rotate towards vertical orientations to induce Myosin II recruitment to the membrane as a function of the angle of the interface. The fast phase of germ band extension usually occurs over approximately 30 minutes, which is followed by mitotic cell divisions. This results in displacement of the observed cells of the germ band from the imaging field by the dividing cells. A mutation in cell-cycle regulating String protein allows us to potentially extend the intercalation window by hindering the mitosis. Using the String mutant, this study aimed to answer whether cell divisions are critical for termination of the fast phase of the germ band extension process, specifically by measuring whether the planar polarity of Myosin II recruitment and contraction/elongation behavior is prolonged in the String mutant. The results support that the anisotropic distribution of Myosin II, and the contraction/elongation behavior are partially preserved in the String mutant. This suggests that the mitotic cell divisions play a role in the termination of the fast phase of the germ band extension, but there are likely other mechanisms that are required for the transition between the germ band elongation phases.

Publication Statement

Copyright is held by the author. Permanently suppressed.

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