Hi, I pulled out mouse embryonic stem cells from -80 (where they have been for a week when I froze them down) and plated them on gelatin plates without feeders. The next day I observe these round structures around the colonies. Can anyone identify what they are? We know its not contamination and my ES media contains antibiotics and plasmocin and is freshly made. And these are not degenerating MEFs since I didn't use feeders in my ell culture.

Thanks in advance for your suggestions!