Meeting Abstract

S2-2.2  Jan. 4  A cellular molecular clock is ticking during proximo-distal limb outgrowth PASCOAL, Susana*; CARVALHO, Cla�dia; RODRIGUEZ-LE�N, Joaqu�n; DELPHINI, Marie Claire ; DUPREZ, Delphine; THORSTEINSD�TTIR, S�lveig ; PALMEIRIM, Isabel; Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho; Instituto Gulbenkian de Ci�ncia; Instituto Gulbenkian de Ci�ncia; CNRS, Universit� Pierre et Marie Curie; CNRS, Universit� Pierre et Marie Curie; Departamento de Biologia Animal, Faculdade de Ci�ncias, Universidade de Lisboa; Life and Health Sciences Research Institute (ICVS), School of Health Sciences, University of Minho spascoal@ecsaude.uminho.pt

Temporal control can be considered the fourth dimension in embryonic development. The identification of the somitogenesis molecular clock brought new insight into how embryonic cells measure time. We provide the first evidence for a molecular clock operating during proximo-distal limb outgrowth and patterning, by showing that the expression of the somitogenesis clock component hairy2 cycles in autopod limb chondrogenic precursor cells with a 6 hour periodicity. We determined the time period required to form an autopod skeletal limb element and propose that an autopod limb skeletal element is formed by cells with �n� and �n+1� hairy2 expression cycles. This work demonstrates that temporal control exerted by cyclic gene expression is not an exclusive property of the somitogenesis process, leading us to the exciting possibility that a molecular clock can be operating in many embryonic tissues with tissue-specific time periods, controlling the formation of various morphological units.