Differential expression of myogenic regulatory genes and Msx‐1 during dedifferentiation and redifferentiation of regenerating amphibian limbs

Abstract

An amputated limb of an adult urodele amphibian is capable of undergoing regeneration. The new structures form from an undifferentiated mass of cells called the regenerative blastema. The cells of the blastema are believed to derive from differentiated tissues of the adult limb. However, the exact source of these cells and the process by which they undergo dedifferentiation are poorly understood. In order to elucidate the molecular and cellular basis for dedifferentiation we isolated a number of genes which are potential regulators of the process. These include Msx‐1, which is believed to support the undifferentiated and proliferative state of cells in the embryonic limb bud; and two members of the myogenic regulatory gene family, MRF‐4 and Myf‐5, which are expressed in differentiated muscle and regulate muscle‐specific gene activity. As anticipated, we find that Msx‐1 is strongly up‐regulated during the initiation of regeneration. It remains expressed throughout regeneration but is not found in the fully regenerated limb. The myogenic gene MRF‐4 has the reverse expression pattern. It is expressed in adult limb muscle, is rapidly shut off in early regenerative blastemas, and is only reexpressed at the completion of regeneration. These kinetics are paralleled by those of a musclespecific Myosin gene. In contrast Myf‐5, a second member of the myogenic gene family, continues to be expressed throughout the regenerative process. Thus, MRF‐4 and Myf‐5 are likely to play distinct roles during regeneration. MRF‐4 may directly regulate muscle phenotype and as such its repression may be a key event in dedifferentiation. Myf‐5 may play a role in maintaining a distinct myogenic lineage during regeneration. © 1995 Wiley‐Liss, Inc.

Inhibition of zebrafish fin regeneration using in vivo electroporation of morpholinos against fgfr1 and msxb

“…Msxb was chosen as msx orthologs have been demonstrated to be expressed during regeneration in many different species (Akimenko et al, 1995;Crews et al, 1995;Reginelli et al, 1995;Simon et al, 1995;Carlson et al, 1998;Koshiba et al, 1998;Heber-Katz, 1999;Nechiporuk and Keating, 2002;Poss et al, 2002a,b) and there are data supporting a crucial functional role in regeneration in other vertebrates (Odelberg et al, 2000;Beck et al, 2003;Han et al, 2003).…”

“…Our second knock-down experiment utilized Msxb, as msx genes have been postulated to play a role in regeneration due to their specialized expression patterns during newt and axolotl limb regeneration (Crews et al, 1995;Simon et al, 1995;Carlson et al, 1998;Koshiba et al, 1998), murine digit tip regeneration (Reginelli et al, 1995;Han et al, 2003), murine ear punch healing (Heber-Katz, 1999), and zebrafish heart (Raya et al, 2003) and caudal fin regeneration (Akimenko et al, 1995;Nechiporuk and Keating, 2002;Poss et al, 2002a;Kawakami et al, 2004). There is also some correlative evidence for functional roles for Msx proteins in regeneration.…”

Mechanisms of urodele limb regeneration

“…Approaches to examining gene activity during regeneration involve quantifying the expression of individual genes and global analyses of gene and protein expression. Individual genes associated with progenitor status that are upregulated during blastema formation are msx1 , msx2 , nrad , rfrng , and notch (Cadinouche, Liversage, Muller, & Tsifildis, 1999; Carlson, Bryant, & Gardiner, 1998; Crews et al., 1995; Géraudie & Ferretti, 1998, for a review; Koshiba, Kuroiwa, Yamamoto, Tamura, & Ide, 1998; Shimizu‐Nishikawa, Tsuji, & Yoshizato, 2001; Simon et al., 1995). Msx1 inhibits myogenesis (Woloshin et al., 1995) and its forced expression in mouse C2C12 myotubes causes cellularization and reduced expression of muscle regulatory proteins (Odelberg, Kollhof, & Keating, 2001).…”

Looking proximally and distally: 100 years of limb regeneration and beyond

“…Hoxa and d, and Meis genes are involved in PD patterning (Gardiner et al, 1995;Torok et al, 1998;Mercader et al, 2005). Hoxd 10 is expressed at a 2-3-fold higher level in proximal versus distal blastemas (Simon and Tabin, 1993;Simon et al, 1995Simon et al, , 1997. Hoxa 9 is expressed throughout both proximal and distal blastemas, but Hoxa 13 expression is 30% higher in distal versus proximal blastemas (Gardiner et al, 1995).…”