Positioning of the LCM cap on the yolk sac A: The yolk sac can be placed within the black ring on the LCM cap (a, 20× magnification) or outside of it (b, 100× magnification). Avoid overlapping the yolk sac with previously collected cells, with the black ring, and with the clear railing. Because our RNA extraction method exposes the entire cap to the denaturing solution, RNA from all captured cells inside and outside of the black ring will be obtained