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. 2013 Sep 23;7:158. doi: 10.3389/fncel.2013.00158

FIGURE 1.

FIGURE 1

Priming and boosting model of ASE asymmetry. ASEL: (1) The first step of promoting the ASEL cell fate occurs six cell divisions before the postmitotic ASEL is born. A transient pair of T-box transcription factors TBX-37/38 acts on the downstream primer element of lsy-6 miRNA to open up the chromatin. (2) The priming event allows boosting of lsy-6 miRNA levels by the CHE-1 transcription factor in the ASEL mother cell, leading to high levels of the miRNA in the postmitotic ASEL neuron. (3) The lsy-6 miRNA directly inhibits the ASER promoting transcription factor COG-1, and allows the ASEL promoting transcription factor DIE-1 to be expressed. (4) DIE-1 then activates ASEL effector genes and represses the ASER cell fate. ASER: (1) Notch is expressed in the ASER precursor and inhibits the lsy-6 priming event. Therefore, the lsy-6 miRNA expression level cannot be boosted as the chromatin remains compact. (2) Consequently, in the postmitotic ASER neuron, the COG-1 transcription factor is expressed, which activates another miRNA, mir-273. (3) mir-273 directly inhibits the ASEL promoting transcription factor DIE-1, and therefore promotes the ASER fate.