These mutants show impaired blastema proliferation, which is consistent with the normal gene expression in the blastema.
We performed a detailed gene expression analysis using the adult fin regenerate and found that the genes are expressed in different regions within the blastema and wound epidermis (Fig.
Looking back at previous studies, a number of reports have described domains of gene expression in the wound epidermis and blastema.
In the wound epidermis, the bmp2 and ptcl genes, in addition to being expressed in the same cells of the basal layer of the epidermis as shh, are also expressed in a subset of blastema cells at the peripheral region (Laforest et ai, 1998) that are fated to the osteoblast lineage (Smith et ai, 2006; Brown et ai, 2009).
Furthermore, Nechiporuk and Keating (2002) suggested that the blastema cells are partitioned into the proliferative proximal cells and the most distal non-proliferative cells that express msxb.
However, it was recently proposed that several cell types such as skeleton, muscle, Schwann cells, and epidermis are produced from progenitor cells with restricted potential during regeneration (Kragl et al, 2009), suggesting that the blastema is a heterogeneous collection of progenitor cells with restricted fates that are not completely dedifferentiated to a pluripotent state.
For some reason, people and other nonurodele vertebrates lack this ability to create a blastema.
Gardiner, both at the University of California, Irvine, have turned to salamanders called axolotls to study how a blastema transforms itself into a limb.
The blastema first specifies which cells will form the axolotl "hand," concludes Bryant.
While a limb blastema can produce its own FGF-2, the scientists believe it needs an initial supply from nerves before it becomes self-sufficient.
The most significant seems to be that the worms do not dedifferentiate cells to create the blastema.