Abstract
Ephrin receptors are the most common tyrosine kinase effectors operating during development. Ephrin receptor genes are reported to be up-regulated in the regenerating tail of the Podarcis muralis lizard. Thus, in the current study, we investigated immunolocalization of ephrin receptors in the Podarcis muralis tail during regeneration. Weak immunolabelled bands for ephrin receptors were detected at 15–17 kDa, with a stronger band also detected at 60–65 kDa. Labelled cells and nuclei were seen in the basal layer of the apical wound epidermis and ependyma, two key tissues stimulating tail regeneration. Strong nuclear and cytoplasmic labelling were present in the segmental muscles of the regenerating tail, sparse blood vessels, and perichondrium of regenerating cartilage. The immunolocalization of ephrin receptors in muscle that gives rise to large portions of new tail tissue was correlated with their segmentation. This study suggests that the high localization of ephrin receptors in differentiating epidermis, ependyma, muscle, and cartilaginous cells is connected to the regulation of cell proliferation through the activation of programs for cell differentiation in the proximal regions of the regenerating tail. The lower immunolabelling of ephrin receptors in the apical blastema, where signaling proteins stimulating cell proliferation are instead present, helps maintain the continuous growth of this region.
Highlights
Among amniotes, only lizards regenerate a large organ such as their tail after loss (Alibardi, 2014, 2015, 2017a, 2018; Bellairs & Bryant, 1985; Cox, 1969; Fisher et al, 2012; Gilbert et al, 2015; Hughes & New, 1959; Lozito & Tuan, 2016)
Bioinformatics and Western blotting Bioinformatics analysis using the Clustal-W Muscle Program showed that at least three ephrin-receptor proteins in the lizard Anolis carolinensis possessed possible epitopes recognized by the antibody employed here; in particular, ephrin receptor-B4 showed a higher identity in comparison to ephrin receptor-B2 and -B3 (Figure 2)
The high up-regulation of ephrin receptors detected by previous transcriptome research (Vitulo et al, 2017a) in combination with the results of the present study suggest that ephrin receptors are present in the regenerating tail
Summary
Only lizards regenerate a large organ such as their tail after loss (Alibardi, 2014, 2015, 2017a, 2018; Bellairs & Bryant, 1985; Cox, 1969; Fisher et al, 2012; Gilbert et al, 2015; Hughes & New, 1959; Lozito & Tuan, 2016). While the growing tip of the blastema elongates the tail, the more proximal regions to the tail stump differentiate into axial tissues (Alibardi & MeyerRochow, 1989). The latter comprise a cartilaginous cylinder replacing the vertebral column and encasing the ependymal tube derived from the spinal cord and segmental myomeres of similar dimension (Figure 1). Regenerating muscles gradually grow from pro-muscle aggregates derived from the local fusion of myoblasts that give rise to elongating myotubes, while the segregated fibroblasts form the connective myosepta (Alibardi, 1995; Cox, 1969; Hughes & New, 1959)
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