The Apical Ectodermal Ridge (AER) is one of the main signaling centers during limb development. It controls outgrowth and patterning in the proximo-distal axis. In the last few years a considerable amount of new data regarding the cellular and molecular mechanisms underlying AER function and structure has been obtained. In this review, we describe and discuss current knowledge of the regulatory...

Although the association between psoriasis and arthritis has been known since the original description by Alibert (1818), it is only recently that the condition has become widely acknowledged as a disease sui generis (Vilanova and Pifiol, 1951; Coste, Franqon, Touraine, and Loyau, 1958; Wright, 1959). The general acceptance of the disorder stems largely from epidemiological (Baker, 1965), clini...