Abstract
Our studies conducted on reptilian limb muscle development revealed, for the first time, early forelimb muscle differentiation at the morphological and molecular level. Sand lizard skeletal muscle differentiation in the early forelimb bud was investigated by light, confocal, and transmission electron microscopy as well as western blot. The early forelimb bud, filled with mesenchymal cells, is surrounded by monolayer epithelium cells. The immunocytochemical analysis revealed the presence of Pax3- and Lbx-positive cells in the vicinity of the ventro-lateral lip (VLL) of the dermomyotome, suggesting that VLL is the source of limb muscle progenitor cells. Furthermore, Pax3- and Lbx-positive cells were observed in the dorsal and ventral myogenic pools of the forelimb bud. Skeletal muscle development in the early limb bud is asynchronous, which is manifested by the presence of myogenic cells in different stages of differentiation: multinucleated myotubes with well-developed contractile apparatus, myoblasts, and mitotically active premyoblasts. The western blot analysis revealed the presence of MyoD and Myf5 proteins in all investigated developmental stages. The MyoD western blot analysis showed two bands corresponding to monomeric (mMyoD) and dimeric (dMyoD) fractions. Two separate bands were also detected in the case of Myf5. The observed bands were related to non-phosphorylated (Myf5) and phosphorylated (pMyf5) fractions of Myf5. Our investigations on sand lizard forelimb myogenesis showed that the pattern of muscle differentiation in the early forelimb bud shares many features with rodents and chicks.
Highlights
Vertebrate limb muscle differentiation and growth are one of the best known developmental processes, and this knowledge is obtained from chick and mouse embryonic studies
The sand lizard limb bud myogenesis was investigated at stages 21–23 by the use of a light microscope, confocal microscope, transmission electron microscope (TEM), and Western blot
No paired homeobox transcription factor 7 (Pax7)- positive cells are detected in the L. agilis forelimb bud, while in the L. agilis trunk Pax7-positive cells in the myotomes were previously observed at the same stage of embryogenesis (Rupik et al 2012; Lewandowski, unpublished)
Summary
Vertebrate limb muscle differentiation and growth are one of the best known developmental processes, and this knowledge is obtained from chick and mouse embryonic studies. The appearance of buds along the lateral body wall is the first step of limb development (Martin 1998). Both forelimbs and hind limbs develop from the lateral mesodermal plate and grow. The limb buds are composed of undifferentiated mesenchymal cells covered by an ectodermal cell layer. Mesenchymal cells of limb buds express one of the T-box transcription factor (TBX) family genes: TBX5 or TBX4 in the forelimb and hind limb respectively (Gibson-Brown et al 1996). The mentioned transcription factors upregulate fibroblast growth factor 10 (Fgf10) expression in mesenchymal cells.
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
