Diversity, isolation and physiological function of Echinodermata coelomocytes: use of echinoids as model organisms

Author(s)

Vinicius Queiroz Araujo

• Document type: Doctoral Thesis
• Press: São Paulo.
• Institution: Universidade de São Paulo (USP). Instituto de Biociências (IBIOC/SB)
• Defense date: 2020-03-20

Examining board members

Márcio Reis Custódio; Gustavo Muniz Dias; José Eduardo Amoroso Rodriguez Marian; Jose Roberto Machado Cunha da Silva

• Advisor: Márcio Reis Custódio

Abstract

To vertebrates, the circulatory system may be seen as an important system that integrates the organism. Among the roles performed directly by it, through the blood and its components, one of the most important ones is to patrol the body for foreign particles and/or substances. In this context, the blood cells (specifically the leukocytes), are responsible to accomplish this mission. In the invertebrates, within your restrictions, the circulatory system also performs similar functions accomplished by its circulating cells. Depending on the group, these cells have been named hemocytes of coelomocytes. To the echinoderms, the cells in their coelomic cavity (coelomocytes) are involved in most of the immune reactions, being the main effectors responsible to fight against foreign bodies and substances. However, differently from the vertebrates, the level of knowledge about the echinoderm immune effectors is considerably lower. Even to the Echinoidea - the best-studied group in Echinodermata - the basic aspects still needs further studies. Basic questions, such as the diversity of cells in the class Echinoidea, the real number of cell subpopulations in sea urchins, and the physiological role of the less studied cells (e.g. spherulocytes and vibratile cells) remain unsolved. In this context, this study aims to investigate the diversity and the physiological function of echinoderm coelomocytes, using echinoids as model organisms. We found five main cell types, comprising 14 subpopulations, a number significantly different from the pointed out in the general literature (three and four, respectively). The cells of Paracentrotus sea urchins were studied, one of the most important models in echinoderm research (i.e. P. lividus), revealing new cell types to these species. Additionally, we provided a model that explains the maturation sequence of the spherulocytes of Paracentrotus. Still, a detailed characterization of Eucidaris tribuloides vibratile cells\' was made, and on the light of these new data, a discussion on the function of the vibratile cell is provided. Through an unusual flow cytometry technique (i.e. image flow cytometry - IFC), we obtained for the first time gates with isolated coelomocyte subpopulation, and through infection experiments analyzed by IFC, we observed the involvement of vibratile cells in immune reactions. Lastly, we elucidate how red spherulocytes release the echinochrome-A, which is a mechanism completely different from the speculated in the literature, and reported a study case where physiological alterations in a sea urchin seemed to be caused by a bryozoan during a symbiotic association. Thus, the results obtained in this study shed light on some crucial aspects of echinoderm physiology and immunobiology, providing the first steps on these important questions (AU)

• FAPESP's process: 15/21460-5 - Physiological function, chemical composition and ontogeny of Echinoid spherulocytes (Echinodermata).
• Grantee: Vinicius Queiroz Araújo
• Support Opportunities: Scholarships in Brazil - Doctorate