Zebrafish - Blastula Period

Blastula Period

The duration of this period is from 2.25 to 5.25 hours

• Transition from 128 cells to 50% epiboly

• It is called the Blastula period as the blastodisc begins to look ball like here until the onset of Gastrulation

• The orientation of the cleavage plains is indeterminate and the cells do not sit in an organized manner any more

• Embryo enters Midblastula Transition (MBT) where the yolk layer forms (YSL) which occurs when the cells that are closest to the yolk fuse to it and the epiboly begins

“Epiboly, beginning in the late blastula (Solnica-Krezel and Driever, 1994), is the thinning and spreading of both the Yoke Syncytial Layer (YSL) and the blastodisc over the yolk cell, as you might model by pulling a knitted ski cap over your head” – http://zfin.org/zf_info/zfbook/stages/stages.html

The Bastula Period. Drawn By Sally Clarke

Zebrafish: Timeline and Staging of Embryonic Development