Assessment of Extracellular Matrix Remodeling during Tail Regeneration in the Lizard Hemidactylus flaviviridis

Abstract

Epimorphic regeneration, as exemplified by lizard tail, involves the formation of regeneration blastema as a prerequisite for replacement growth. The formation of blastema is preceded by many regressive changes like tissue demolition, histolysis, inflammation, wound closure, dedifferentiation, cell migration and proliferation. The ECM components of a normal tail help maintain the differentiated state of the constituent heterogeneous tissue and tend to prevent cell migration and proliferation. Since the formation of a regeneration blastema involves many key cellular events like dedifferentiation, migration of dedifferentiated and other nomadic cells and cell proliferation, extensive reorganization of the extracellular matrix is likely to be a major event during post-autotomy period. To this end, total GAG content and gelatinase (MMP-2&9) activity were assayed during the first week post-caudal autotomy. The effect of MMP inhibition by doxycycline was also evaluated in terms of the number of days taken for wound closure and blastema formation as well as the length of detail regenerated at the end of twenty days from the time of initiation of growth. Significant progressive decrement in total GAG content up till 96 hours followed by a significant increment at 120 and 144 hours, together with a biphasic increment in gelatinase activity (first during 24-48 hours and second during 96-144 hours) have been recorded. The increased gelatinase activity and the decreased GAG content in the first 96 hours are suggestive of breakdown of proteoglycans and collagens (type IV, V, VII&X). The second phase of increase in GAG content is related with synthesis of hyaluronate, favoring dedifferentiation, proliferation and migration of cells. MMP inhibition by doxycycline significantly retarded tail regeneration. From these results it is concluded that ECM remodeling is crucial in the immediate post-autotomy period for the formation of an effective blastema and that MMPs play a crucial role in the same.