Midblastula

In developmental biology, midblastula or midblastula transition (MBT) occurs during the blastula stage of embryonic development. During this stage, the embryo is referred to as a blastula. The series of changes to the blastula that characterize the midblastula transition include activation of zygotic gene transcription, slowing of the cell cycle, increased asynchrony in cell division, and an increase in cell motility. In developmental biology, midblastula or midblastula transition (MBT) occurs during the blastula stage of embryonic development. During this stage, the embryo is referred to as a blastula. The series of changes to the blastula that characterize the midblastula transition include activation of zygotic gene transcription, slowing of the cell cycle, increased asynchrony in cell division, and an increase in cell motility. Before the embryo undergoes the midblastula transition it is in a state of fast and constant replication of cells. The cell cycle is very short. The cells in the zygote are also replicating synchronously, always undergoing cell division at the same time. The zygote is not producing its own mRNA but rather it is using mRNAs that were produced in the mother and loaded into the oocyte in order to produce proteins necessary for zygotic growth. The zygotic DNA (genetic material) is not being used because it is repressed through a variety of mechanisms such as methylation. This repressed DNA is sometimes referred to as heterochromatin and is tightly packed together inside the cell because it is not being used for transcription.