SHEA, E.K.; CALDWELL, S.; LAPPING-CARR, G.; HOLLYDAY, M.; Bryn Mawr College; Bryn Mawr College; Bryn Mawr College; Bryn Mawr College: Programmed cell death in the separating tentacles of the paralarval squid Ommastrephes bartramii.

Newly-hatched squids in the family Ommastrephidae are unique within the decapod cephalopods because their tentacles are joined into a single structure. The fused-tentacles separate during development to form the two adult tentacles. Although the ontogeny of the tentacles is well documented, the separation mechanism has never been examined. We used transmission electron microscopy (TEM) and Terminal deoxynucleotidyl transferase mediated dUTP nick end labelling (TUNEL) assays to assess whether cells in the fused tentacle of Ommastrephes bartramii die via pre-programmed cellular death (PCD). We found the transverse muscle mass is TUNEL positive, indicating genomic DNA is being cleaved and a PCD pathway has been initiated. However, the characteristic nuclear morphology associated with apoptosis does not appear to be present. TUNEL positive cells are dispersed throughout the transverse muscle mass, and not exclusively at the midline, indicating the separation process is not a localized disruption but involves a radical re-organization of the entire musculature. These results suggest that during separation, the fused-tentacles are probably not fully functional, and not useful for prey capture.