I am currently working with 72 hpf and 120 hpf Cdk5 zebrafish (both wild-type and knockout). I have stained my retinal cryosections with anti-parvalbumin (mouse) and anti-islet1 (mouse or rabbit) primary antibodies. I have currently stained 20 samples and I was able to detect parvalbumin positive cells continuously in both wild-type and knockouts, but not islet1 positive cells. Does anyone have any idea why this keeps on happening?

Thanks in advance!