The signals underlying epidermal specification during embryogenesis and the maintenance of L1 identity in meristems and organ primordia are largely unknown. This lack of information is probably attributable to two factors. Firstly, abnormal epidermal specification leads to the production of subviable embryos, making the isolation and characterisation of mutants difficult. Secondly, there may be a high level of genetic and functional redundancy between some of the factors involved in these critical developmental processes. Despite these problems some indications regarding the types of signalling molecules which could be involved, and how they may be perceived have emerged from recent research.
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