Abstract
This study describes the temporal pattern of posterior positional identity in mouse limb bud cells. To do this wedges of tissue from the posterior edge of mouse limb buds at various stages (limb stages: Wanek et al., 1989b. J. Exp. Zool. 249, 41–49) were grafted to the anterior edge of a host chick embryo wing bud. Grafts of mouse posterior cells are able to induce the formation of supernumerary digits every time when they are taken from buds from stage 3 through stage 6. At stage 7, the frequency declines and by stage 8 the chick cells no longer respond. The results indicate a change in tissue properties at stage 7, which progresses by stage 8 to the point at which posterior positional identity is no longer detectable by this assay. These temporal changes in this aspect of limb pattern formation can be used as an additional criterion to guide the identification of genes involved in the specification of posterior positional identity.
Highlights
A major conclusion from studies of pattern regulation in vertebrate limbs is that cells in different positions within the developing limb bud are nonequivalent (Lewis and Wolpert, 1976) in terms of their positional properties
A total of 49 host chick limbs were analyzed for the presence of supernumerary digits induced by wedges of posterior cells from mouse limb buds grafted to the anterior margin
The frequency and degree to which posterior mouse cells are able to stimulate a supernumerary response in anterior chick cells decline as a function of mouse limb
Summary
A major conclusion from studies of pattern regulation in vertebrate limbs is that cells in different positions within the developing limb bud are nonequivalent (Lewis and Wolpert, 1976) in terms of their positional properties. This is most dramatically demonstrated when cells from different positions are brought into contact by grafting, the result of which is the stimulation of growth, the insertion of new pattern between the confronted cells, and the restoration of local continuity in the array of positional states or identities (French et aZ., 1976; Bryant et ak, 1981).
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