MODIFICATION OF THE PHALANGEAL PATTERN OF THE DIGITS IN THE CHICK-EMBRYO LEG BUD BY LOCAL MICROINJECTION OF RA, STAUROSPORIN AND TGF-BETA-S

Many experimental studies show that in the avian chick limb the digits are specified at early stages of development by characteristic concen trations within the limb mesoderm of a still unidentified morphogen di ffusing from the posterior margin of the bud, linked with a specific p attern of homeobox gene expression. In all these studies, digits are d istinguished by their size, morpholgy and phalangeal pattern rather th an by their position within the autopodium. In this work we report the induction of digits that have otherwise normal morphology but lack an interphalangeal joint. This suggests that the patterning of these joi nts is not necessarily linked to the control of the outgrowth of the d igital rays. Missing interphalangeal joints were induced by microinjec tion into the third interdigital space of the leg bud of stage 28 to 3 1 chick embryos of retinoic Acid (RA), staurosporine and TGF beta1 and beta2, but not by microinjection of FGF or EGF. Our results also sugg est that the pattern of insertion of the long tendons and the formatio n of the flexor cutaneous pad at the plantar surface of the digits are both linked to the establishment of the interphalangeal joints.