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Presenting Author(s) Takanori Amano
Abstract Title Specification of the most anterior digit 2 in the developing chick wing bud.
Full author List Takanori Amano, Hiroyuki Ide, Koji Tamura
Text of abstract

All digits are originated from appropriate positions in the developing limb bud, and the position of each digit is thought to be determined according to the distance from the ZPA. In the chick wing bud, digit 4 is formed adjacent to the ZPA and digit 2 sited in the foremost part of the bud is formed in the most distant region from the ZPA.

To elucidate the mechanism of specification of digit 2, we performed several surgical experiments. The ZPA grafted to the anterior-most region caused the anterior mesenchyme to change its normal prospective fate to a posterior one as described previously. In this case, digit 3 always differentiated additionally in this most-anterior region (non-digit region), where no digits are normally derived, and an extra digit 4 was often formed there. However, the formation of an additional digit 2 was not observed in this non-digit region, and the additional digit 2 arose from the expanded digit 2 region, which normally gives rise to digit 2. To further investigate the different abilities of the anterior non-digit and digit regions to form digits, we excised the wing bud except for the target region (parallel to somite 16 for the non-digit region, somite 17 for digit 2 region, and somite 18 for digit 3 region) and grafted the ZPA tissue on the distal face of each region. Typically, all three regions gave rise to some digits, and, interestingly, the non-digit region (parallel to somite 16) never formed digit 2, although digits 3 and 4 were formed. These results, together with the results of molecular marker analysis using hoxd, tbx3, bmp4, fgf4, and an anterior marker, mario, suggest that the anterior non-digit region inhibits digit formation, particularly formation of digit 2. In normal development, this region may be involved in restricting the digit 2 region and in limiting the number of digits.

Which session is your work most relevant to: Limb patterning