MORPHOGENETIC POTENTIAL OF THE CHICK LEG INTERDIGITAL MESODERM WHEN DIVERTED FROM THE CELL-DEATH PROGRAM

There is evidence that the interdigital mesoderm may be in an undiffer entiated state, For example, under experimental manipulation in vivo i t may be diverted from cell death to digit formation, In the present w ork we wanted to analyze the maximum morphogenetic potential of the in terdigital cells, To do this we made recombinant limbs of three types, the first using dissociated-reaggregated leg interdigital mesoderm, t he second using the same tissue but without dissociation and the third adding a piece of polarizing region to the dissociated interdigit, In all three the massive cell death of the interdigit failed to occur, T he first type of recombinant formed a small nodule of cartilage while the other two formed a well-developed digit, Our data indicate that th e maximum morphogenetic potential of the interdigital tissue appears c onstrained to form digits and that dissociation of the tissue decrease d this ability; polarizing region restores the ability of dissociated cell recombinants to form a digit, We also analyzed in these recombina nts the expression of a battery of genes implicated in interdigital ce ll death or in digital morphogenesis. The pattern of expression of eac h gene analyzed was identical in the three types of recombinant limbs, The expression of Msx1 and Msx2 genes was maintained under the ridge indicating a good interaction between the interdigital cells, both dis sociated and undissociated, and the apical ridge, The expression of Ho xd-12, Hoxd-13 and Hoxa-13 genes was maintained in the recombinants, i ndicating that these cells carry information about their autopodial or igin, and this correlates well with their distal restricted morphogene tic potential. Finally, the patterns of expression of the Bmp-2, Bmp-4 and Bmp-7 genes indicated that they are independently regulated in th e recombinants and that Bmp-4 and Bmp-7 have wider expression domains than the areas of cell death that were only detected under the regress ing apical ridge during day 3 of the experiment. (C) 1997 Wiley-Liss, Inc.