Cytoarchitecture Of The Tail Regeneration In Scincella Tsinlingensis

The degree of regeneration seems to be different in different species and development stages,and this ability is gradually lost with the evolution of animals,which makes the regulatory mechanism of regeneration always be a research hotspot of developmental biology and one of the most challenging scientific problems in life sciences.Tail regeneration in lizards involve wound healing and tissues differentiation,which have been studied as an excellent amniote model of tissue regeneration.To explore the cytoarchitecture of the tail regeneration in lizard,it not only can enrich the morphological data of reptile tissue regeneration in China,but also provide a theoretical basis for elucidating the molecular mechanism of the tail regeneration in lizard at the molecular,cellular and tissue levels.The ovoviviparous lizard Scincella tsinlingensis is an endemic species to China.Multiple techniques about morphology,histology,histochemistry and immunohistochemistry are used to investigate morphological characteristic and cytoarchitecture of regeneration following tail autotomy in the lizard,which will help to unveil key gross morphological and histological criteria used to define the stages of tail regeneration.The main results as followed:1.The average growth rate of the regenerating tail in S.tsinlingensis shows seasonal variation,i.e.,0.788±0.297 mm/d in spring and winter and 1.014±0.38 mm/d in summer and autumn.There is a significant positive correlation between the length of regenerative tail and the regenerative days.In spring and winter,y=0.7097x-0.3045(r=0.9845,p<0.01),in summer and autumn y=0.8645x+0.1516(r=0.9779,p<0.01).2.Based on gross anatomy and histology,the process of the tail regeneration contains four stages in S.tsinlingensis,involving wound healing,blastema formation,cell differentiation and tail growth,which also can be subdivided into seven stages accordingto its regeneration duration.Stage I,0-48 h post-autotomy,the main feature is that autotomized vertebra is exposed but no adjacent muscle or connective tissue retracted.Spinal cord retracts within neural canal and is capped distally by a small blood clot and then epidermis begins to collapse around the wound site;Stage II,24 h-7 d post-autotomy,the vertebrae is exposed and then adjacent muscle or connective tissue retracted.The large blood clot covers the entire wound surface.The epidermis collapses around the wound site.Meanwhile,the wound epithelial cells proliferate and begin to spread across autotomy surface deep to clot.The blastema appears between retracted spinal cord and overlying clot;Stage III,5-10 d post-autotomy,the clot is lost and wound epithelium is completely exposed which continues to proliferate and thicken,thus the apical epithelial cap(AEC)is formed.The blastema spreads beyond neural canal to AEC distal end of the tail deep to wound epithelium.In addition,the angiogenesis begins in the blastema and ependymal tube and axons start to grow into blastema;Stage IV,7-15 d post-autotomy,regenerating tail is dome-shaped and its width is longer than length(length / diameter < 0.5);Stage V,10-25 d post-autotomy,regenerating tail is an elevated dome and width is similarly longer than length(0.5 < length / diameter < 1.0).The cartilage skeletons are formed around the ependymal tube and muscle tissue begins to differentiate.Epidermis appears to keratinize coincided with scales formation;Stage VI,20-30 d post-autotomy,regenerating tail is a tapering cone approaching a length: width of 1.0.The differentiated dermis appears for the first time,while the differentiation of cartilage,muscle and adipose tissue are about to be completed;Stage VII,45-160 d post-autotomy,regenerating tail is a tapering cone and its length is longer than width(length / diameter > 1.0).Proximal portion of the regenerate tail is equal in diameter to the distal portion of original tail and then pigmentation begins.3.The external morphology of the regenerative tail in S.tsinlingensis is similar to the original tail,but its internal structure is significantly different from the original tail.The main distinction is that the rigid hyaline cartilage tube in regenerative tail replaces the endoskeleton formed by the vertebrae in original tail.Regenerated muscle bundles with a high connective tissue content are loosely organized radially around the cartilage tube,but the original tail muscle tissue with the regular arrangement is divided into four quadrants.Theregenerative tail has a limited regenerative spinal cord compared to the original tail,but can support axonal growth.The ependymal layer of the the original spinal cord is pseudostratified with multiciliated cells and primary monociliated cells,but the ependymal layer cells of the regenerated spinal cord are organized into monolayer with a few of bicilicated cells.