Is There a Unifying Mechanism Regulating Zygotic Transcription?
One thing that bothers developmental biologists is that there isn’t a unifying principle regarding the regulation of zygotic transcription since the sea urchin and mouse do not display a type of mid-blastula transition. It has been noted that the cell cycle may be one regulatory point. In mouse the cell cycle is very long and it can be argued that there is ample time for transcription to occur. Recall, as well, that that sea urchin has a number of blastomeres of varying size, which undergo asynchronous cleavage. Question: • Can asynchronous cleavage be used to explain why the sea urchin does not appear to have a midblastula transition? How would you test this? One observation that refutes the notion that zygotic transcription is linked to the cell cycle is that in mouse, transcription can occur even if the cell cycle is arrested in S phase. Interestingly, zygotic transcription occurs regardless of replicative state or what cell cycle stage the embryo is in. As a result it has been sugg
