Pc-AIF1 Is Expressed in Hemocyte-Rich and Neural Tissues and Links Immune Response and Regeneration in the Snail Model Pomacea canaliculata

Allograft inflammatory factor-1 (AIF1) is a conserved calcium-binding protein involved in inflammatory and neuro-immune responses and expressed in Pomacea canaliculata (Pc-AIF1) during cephalic tentacle regeneration. Here, we investigated the expression and distribution of Pc-AIF1 in control conditions and during cephalic tentacle regeneration. A transcriptomic analysis of 315 RNA-seq datasets revealed maximal Pc-AIF1 expression in circulating hemocytes and hemocyte-rich tissues. Pc-AIF1 was also highly expressed in neural ganglia. Fluorescence in situ hybridization (FISH) evidenced Pc-AIF1 in circulating hemocytes and in the phagocytic hemocyte aggregates in the posterior kidney. qPCR showed the constitutive expression of Pc-AIF1 in cerebral ganglia. FISH experiments showed Pc-AIF1-positive cells within the cephalic tentacle blastema at 24 h post-amputation (hpa). Even if the amputation left them untouched, both the ipsilateral and contralateral cerebral ganglia increased Pc-AIF1 expression until 48 hpa. Immunocytochemical experiments evidenced positive cells to RCA120 (a microglial marker in mammals) among circulating hemocytes, in the connective tissue surrounding the cerebral ganglia, and within the regenerating tentacles. These findings suggest that Pc-AIF1 is a neuro-immune marker constitutively expressed in hemocyte populations and neural tissues; it is associated with the immediate hemocyte response to wounding and the neuro-immune interplay during the regeneration of sensory organs.