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Bioessays. 2011 Jan;33(1):13-20. doi: 10.1002/bies.201000090. Epub 2010 Oct 15.

The "occlusis" model of cell fate restriction.

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Department of Human Genetics, Howard Hughes Medical Institute, University of Chicago, Chicago, IL, USA.


A simple model, termed "occlusis", is presented here to account for both cell fate restriction during somatic development and reestablishment of pluripotency during reproduction. The model makes three assertions: (1) A gene's transcriptional potential can assume one of two states: the "competent" state, wherein the gene is responsive to, and can be activated by, trans-acting factors in the cellular milieu, and the "occluded" state, wherein the gene is blocked by cis-acting, chromatin-based mechanisms from responding to trans-acting factors such that it remains silent irrespective of whether transcriptional activators are present in the milieu. (2) As differentiation proceeds in somatic lineages, lineage-inappropriate genes shift progressively and irreversibly from competent to occluded state, thereby leading to the restriction of cell fate. (3) During reproduction, global deocclusion takes place in the germline and/or early zygotic cells to reset the genome to the competent state in order to facilitate a new round of organismal development.

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