how you think about fragmentation? Phagocytosis? degeneration? apoptosis?

Maybe the Hoechst (or DAPI) staining period is not sufficient. Sometimes I faced it in bovine and porcine embryos (Morulae or blastocysts) when the staining time is less than 10 minutes. Try to increase the time of staining.

thanks for your answer. I have tried 30 minute at the first but at the end I saw for Hoechst staining 1 minute can be fine and you can have same result. even with lower concentration. this staining is ROS with Hoechst.

Three stories:

1) I teach embryology and in the human embryology textbook is a photograph of a morula where only 3 of the cells have stained nuclei.

2) I worked in Australia with a team of embryo-transfer veterinarians. They picked what they thought were perfect morulae to transfer, but got poor pregnancy rates.

3) I worked on bovine in vitro oocyte maturation. My colleague mentioned what wonderful morulae I had generated.

1) The "embryo" was in fact apoptotic.

2) Careful examination of the morula stage embryos using a portable inverted microscope revealed that what were being classed as excellent grade morulae where in fact fragmented eggs.

3) I never fertilized the oocytes. They had fragmented into what an embryo-transfer vet thought were excellent morulae.

Oocytes and early embryos bleb when undergoing apoptosis. Such blebbing embryos look like morulae.

The rule I use to distinguish between morulae or blebbed oocytes and embryos: How many sizes of blastomeres do you have? If you have more than two different sizes of purported blastomers, it is likely a apoptotic embryo or oocyte. Especially be suspicious if you have a gradation of sizes.

I could not see the relative size of blastomeres from your image.