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Cell. 2012 Dec 7;151(6):1229-42. doi: 10.1016/j.cell.2012.10.049. Epub 2012 Nov 29.

Embryonic priming of a miRNA locus predetermines postmitotic neuronal left/right asymmetry in C. elegans.

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Department of Biochemistry and Molecular Biophysics, Howard Hughes Medical Institute, Columbia University Medical Center, New York, NY 10032, USA.


The mechanisms by which functional left/right asymmetry arises in morphologically symmetric nervous systems are poorly understood. Here, we provide a mechanistic framework for how functional asymmetry in a postmitotic neuron pair is specified in C. elegans. A key feature of this mechanism is a temporally separated, two-step activation of the lsy-6 miRNA locus. The lsy-6 locus is first "primed" by chromatin decompaction in the precursor for the left neuron, but not the right neuron, several divisions before the neurons are born. lsy-6 expression is then "boosted" to functionally relevant levels several divisions later in the mother of the left neuron, through the activity of a bilaterally expressed transcription factor that can only activate lsy-6 in the primed neuron. This study shows how cells can become committed during early developmental stages to execute a specific fate much later in development and provides a conceptual framework for understanding the generation of neuronal diversity.

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