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Abstract
Homeobox genes encode positional information during primary and secondary axis formation during development. For this reason, the Hox genes have attracted attention in regeneration research as well. At early stages of regeneration, Hox genes have been implicated in wound healing and the dedifferentiation process and at later stages in the patterning of the blastema. We studied the expression of three Abdominal B-type Hox genes in Xenopus: XHoxc10, XHoxa13, and XHoxd13 during normal limb development and during regeneration of limbs and tails. We compared their expression with nonregenerating and with wounded limbs and tails, respectively. We show that the temporal and spatial control of these three Hox genes in blastemas differs from normal development. All three are specific to regeneration, XHoxc10 is up-regulated at the right time and at the site where cells dedifferentiate and undifferentiated cells are recruited, whereas XHoxa13 is reexpressed slightly later in regeneration, when the blastemal cells proliferate and remains on during patterning of the blastema. XHoxd13 is not expressed until relatively late and appears to be involved only in patterning of the blastema.
Figure 2. Posterior Hox gene expression in embryos and developing limbs. In situ hybridisation in stage 30 embryos and various stages of developing limbs. A-D: XHoxc10 expression. E-H: XHoxa13 expression. I-L: XHoxd13 expression. White arrows indicate anterior expression boundary in the CNS. For the limbs, the orientation is natural, i.e., the viewer is looking down dorsally, proximal is to the left, anterior is down, and posterior up.
Figure 3. Posterior Hox gene expression in regenerating limbs. Stage 54 limbs were amputated at knee level and left to regenerate for 1 (A,E,I), 3 (B,F,J), or 5 (C,G,K) days before they were subjected to in situ hybridisation. Nonregenerating stage 57 limbs were amputated at knee level and left to heal for 5 days (H,L). D: Stage 54 limb was wounded in the flank and left to heal for 1 day (black arrow points to the wound). A-D: XHoxc10 expression, (E-H) XHoxa13 expression, and (I-L) XHoxd13 expression. Hash marks indicate level of resection. Looking down dorsally, proximal to the left and anterior down.
Figure 4. Posterior Hox gene expression in regenerating and wounded tadpole tails. In situ hybridisation of posterior Hox genes after tail resection or wounding. A-C: XHoxc10 expression. D-F: XHoxa13 expression. G-I: XHoxd13 expression. Stage 50-52 tails were amputated at mid-tail level and left to regenerate for 1 (A,D,G) or 3 days (B,E,H). Stage 54 tails were wounded mid-tail and fixed 1 day later (C,F,I). The black arrows point to the staining in the neural tube. All pictures are side views with rostral to the left.
hoxc10 (homeobox C10) gene expression in Xenopus laevis embryo via in situ hybridization, NF stage 29 & 30, lateral view, anterior left.
hoxa13(homeobox A13) gene expression in Xenopus laevis embryo via in situ hybridization, NF stage 29 & 30, lateral view, anterior left.
hoxd13 (homeobox D13) ggene expression in Xenopus laevis embryo via in situ hybridization, NF stage 29 & 30, lateral view, anterior left.
