Résumé :
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Communication n° 128. Despite increasing interest for cell transdifferentiation, little is known about its genetic control. Here, we determine that the adult fruit fly heart is formed during metamorphosis by a remodelling of the differentiated and already functional larval cardiomyocytes. The process occurs without cell proliferation and is mediated by a regulation of the Hox genes Ultrabithorax (Ubx) and abdominal-A (abdA) expression and function. In particular, abdA expressing myocytes acquire a novel differentiated state: while they form contractile heart myocytes in the larval cardiac tube, their shape, function and molecular characteristics are modified at metamorphosis while they become the target of specific innervations. Remarkably, abdA controls the acquisition of both larval and adult differentiated states, indicating that the specificity of AbdA action is switched at metamorphosis towards a new differentiation program that leads these myocytes to transdifferentiate. Moreover, we show that this developmental switch is mediated by the steroid hormone ecdysone. Our results thus unravel a mechanism for cardiomyocytes transdifferentiation, which involves a steroid dependent modification of Hox function.
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