So... Frog Day. We had a preview of the slimy, squirmy critters the day before when we helped collect eggs and testes. Frog day was dedicated to the frog embryo. It was an amazing nod to the cutting-edge and to history.
|32-cell stage frog embryos|
First was a look forward. One can imagine that as the embryo cleaves, that you just pinch the existing membrane around the cytoplasm to get many new cells. To test this, we inhibited the actin cytoskeleton during cleavage - the mechanism by which the membrane 'pinches' along the cleavage furrow. Without actual cleavage and fascinating thing occurs - white stripes start appearing in the pigmented animal half.
What are these stripes - they're new membrane that is being laid down during cleavage. So its not just a pinching. New material must also be added. Interestingly, as time continues, the orientation of the would-be cleavages are preserved. This is most likely because the mitotic spindle orientations remain uninterrupted.
In the afternoon, we went back in time to revisit THE classic frog developmental biology experiment - the Spemann Organizer. This is an embryo manipulation experiment in which pieces of embryos are transplanted. I never in a million years thought I would recreate this landmark experiment. Yet, some how I successfully excised a piece of the dorsal lip - through which cells invaginate during gastrulation. Then transferred the piece of dorsal lip into a new embryo in an attempt to make a second access - a Siamese twin. We also did a modification of this experiment with later stage neurula-stage embryos. I did eight transplants hoping to have some survive and one actually twin. Well, I got 3 to twin to varying degrees!! One of them was even better than a twin. I made a triplet. The easiest way to count heads is to look for a black dot, called the cement gland - this helps the tadpole attach to the bottom until its able to swim.
|Hall of fame from the class. The one in the middle with 2 visible black dots is mine.|
|Twinned neurula (earlier stage). Note that the future notochord (line down the middle) splits near the bottom.|