Transcriptional regulation during early cleavage stages

In the 64 or 110-cell embryo, developmental fate of most of the cells (blastomeres) is determined.  By the 16-cell stage, each blastomere has already started to express different set of genes.

To understand molecular mechanisms underlying cell differentiation in embryos, it is important to reveal the mechanisms of transcriptional activation and repression of genes in certain lineages of blastomeres.
Ci-ephrinAd/lacZ の発現
A gene expressed in  8 blastomeres of the 16-cell embryo.

The figure on the right side shows an experiment that examined the function of regulatory regions (enhancer) on the DNA molecule flanking on the gene named ZicL.  
In normal embryos, ZicL is expressed in 8 blastomeres of the 32-cell embryo.

A 658-bp upstream sequence of ZicL is sufficient to recapitulate the normal expression pattern of ZicL (A).  When a distal region (Region X) was deleted, the enhancer is only activated in the posterior four blastomeres (B).  In contrast, internal deletion in the proximal region (Region Y) resulted in inactivation of the enhancer only in the posterior four blastomeres.  These results suggest that Region X and Region Y is required for transcriptional activation of ZicL in the anterior and posterior blastomeres, respectively. 
ZicL 遺伝子の転写調節
Next thing to do is identification of proteins (transcription factors) that bind and activate (or repres)
the function of the enhancer.  

*Anno, C., Satou, A. & Fujiwara, S. (2006) Transcriptional regulation of ZicL in the Ciona intestinalis embryo. Dev. Genes Evol. 216: 597-605.