DIGIT TIP REGENERATION CORRELATES WITH REGIONS OF MSX1 (HOX-7) EXPRESSION IN FETAL AND NEWBORN MICE

We report that during mouse fetal development transcripts of Msx1 and Msx2 become progressively restricted to cells that will form more dist al digit structures; the Msx2 expression domain is always more distal than Msx1. At birth both Msx1 and Msx2 are expressed in cells of the n ail bed and hair follicle. We have found that the regenerative ability of mouse digit tips is restricted to levels in which the amputation p lane is within the region of Msx1, but not Msx2, expression in early f etal digits and to levels where both Msx1 and Msx2 are expressed in la te fetal and neonatal digits. Fetal digit tip regeneration is rapid an d completed by birth, whereas neonatal digit tip regeneration requires 4 weeks and is sometimes imperfect. In both fetal and neonatal digits , we find that both Msx1 and Msx2 are expressed during regeneration, b ut not during wound healing associated with proximal amputations where no regenerative response is observed. These data support the hypothes is that the expression of Msx genes are important for digit cells to i nitiate and participate in a regenerative response.