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LBDV laboratory

The formation of the embryonic midline fates

 Embryonic midline fates of the chordate embryo include the notochord, the ventral part of the neural tube and the anterior endoderm.
In ascidians, two rounds of cell divisions of blastomeres called A5.1 and A5.2 of the 16-cell embryo generate precursors of each of these midline structures (Figure 1).



Figure 1. Cell lineage of A5.1 and A5.2 blastomeres, progenitors

of the midline tissues. Embryos are of the vegetal pole view. Black

barconnecting blastomeres reprisents sister cell relationship.

Note that Ciona embryos are bilaterally symmetrical. En: endoderm,

No: notochord, Neu: neural, Mes: mesenchyme.

We have been focusing on the cell fate choice between notochord and neural which takes place when the A6.2/A6.4 blastomeres divide to give rise to A7.3 and A7.7 notochord precursors and A7.4 and A7.8 neural precursors. Following the formation of the precursors of notochord and neural tissue, a distinct set of genes starts to be expressed in each precursor, suggesting that cell-fate specification begins soon after these cell lineages emerge (Figure 2).

Figure 2. Differential gene activation between notochord and neural

lineages. Gene expression was revealed by in situ hybridisation. Zygotic

expression of Ci-Brachyury and Ci-FoxB, both of which encodes a transcription

factor, is initiated in notochord and neural precursors, respectively.


We are analysing the roles of cell-cell interactions and the cell signalling pathways and  transcriptional controls of lineage-specific genes that govern these cell-fate descisions.

Hitoyoshi Yasuo - 26/09/17

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