Chorion and Vitelline Membrane Mechanical Removal: A Method to Prepare Drosophila Oocytes for Direct Observation

- Begin with mature oocytes from fixed ovaries in a saline solution. Mature oocytes bear eggshells consisting of an outer chorion and inner vitelline membrane.

To mechanically remove the chorion and vitelline membrane, place the oocytes between the frosted parts of two pre-treated slides. Move the top slide in straight back-and-forth motions to create friction that rolls the oocytes.

Now, move the top slide at a slight angle to roll the oocytes in another direction. Avoiding circular motion, increase this angle in short increments until the top slide moves perpendicular to the bottom slide. This movement mechanically removes the chorions and vitelline membranes, enabling access for probes or stains into the oocyte.

Oocytes without chorions will appear long and thin, and those without vitelline membranes will have pointed ends. To separate the cleared oocytes from the surrounding debris, transfer the sample mix to a tube, and allow the oocytes to settle to the bottom while the debris floats at the top and can be removed.

In this protocol, we will remove chorion and vitelline membranes from mature Drosophila oocytes.

- To separate the late-stage oocytes, first, add 1 milliliter of PB