New Cell Model for Endosymbiosis Research: Spontaneous Dissociation of Endoderm Cells Based on Tissue Polarity in Coral

Abstract

Regulatory mechanism of marine endosymbiosis in Cnidarian-dinoflagellate association remains unknown. In order to investigate cellular and molecular interactions between symbionts and their host endoderm cells, an homogeneous population of endoderm cell is required. We explore a novel strategy to isolate endoderm cells, based on the polar distribution of different tissues in tentacles of stony coral Euphyllia glabrescens. Inversion of tentacle fragments re-arranges the orientation of endoderm. Change in orientation results in dissociation of both symbiotic and aposymbiotic endoderm cells upon mechanical swirling within an hour. The homogeneity of collected endoderm cells was found to be higher than 95%. Microscopic examination of dissociated symbiotic endoderm cells indicated the presence of multiple numbers of symbionts within a single endoderm cell. Membrane labeling using fluorescent probe FM1-43 demonstrates membrane trafficking between the endoderm cell membrane and the symbiosome membrane that encloses the symbiont. In addition, the fluorescent study revealed significant membrane internalization in aposymbiotic endoderm cells, suggesting a dynamic nature of membrane in these cells. The inverted manipulation of the tentacles also provides an in vitro system to in estigate effects of host tissue arrangement on the photosynthetic activity of resident symbionts. The present work not only provides a new cell preparation for the study of molecular and cell regulation of endosymbiosis in marine invertebrates, but also sheds new insight on the relationship of tissue arrangement and symbiotic activity.