Mfge8 Knockout Affects Tail Resorption Speed During Xenopus Metamorphosis

To elucidate the control mechanism of tail resorption during <i>Xenopus</i> metamorphosis, the expression of <i>mfge8</i>, a macrophage-apoptotic cell bridging molecule that promotes phagocytosis in mammals, was examined. In both <i>Xenopus tropicalis</i> and <i>Xenopus laevis</i>, the <i>mfge8</i> expression in the tail increased significantly during metamorphosis, reaching its peak at the metamorphic climax, when the tail shortens rapidly. This finding suggests that the up-regulation of <i>mfge8</i> at metamorphic climax is involved in the clearance of apoptotic tail muscles. To investigate the significance of <i>mfge8</i> up-regulation, <i>mfge8</i>-deficient <i>X. tropicalis</i> tadpoles were generated using the CRISPR/Cas9 method, and the effects of <i>mfge8</i>-deletion were examined. Delayed tail resorption process was observed in the <i>mfge8</i>-deficient mutants (from 9.8 days [wild type] to 13.2 days [F2 mutant]), suggesting that elevated <i>mfge8</i> expression during the metamorphic climax contributes to the tail resorption.