Evolução molecular de genes do sistema imunológico adaptativo em mamíferos aquáticos

Author(s)

Bruna Cristina Dias

• Document type: Master's Dissertation
• Press: Campinas, SP.
• Institution: Universidade Estadual de Campinas (UNICAMP). Instituto de Biologia
• Defense date: 2021-07-09

Examining board members

Mariana Freitas Nery; Juliana de Abreu Vianna; Marcelo Mendes Brandão

• Advisor: Mariana Freitas Nery

Abstract

Despite the constant microbial challenges from the environment, the body prevents infections by a specific and incredibly diverse system that can fight myriad pathogens. The adaptive immune system (AIS) is a very complex defense mechanism. The AIS has two different groups of cells and molecules, called B and T lymphocytes, that defend against extracellular microbes and intracellular microbes. B lymphocytes exclusively synthesize antibodies - collectively called immunoglobulins (IG) - produced in great variety, each with different DNA sequences and, consequently, different antigen-binding sites. Recombination-activating genes 1 (RAG1) and 2 (RAG2) genes complex catalyzes random assembly of variable (V), diversity (D), and joining (J) gene segments that are present in the genome in numerous copies and generate the enormous variety of the assembled antibodies and antigen receptors. It is believed that the RAGs origin must have been crucial for adaptive immunity, as all of the BCR and TCR genes use the same mechanism of V(D)J rearrangement. The occupation of new environments is a favorable scenario for the emergence and diversification of new species, and the molecular changes taking place in the genome of organisms during this occupation have ceased to be a mystery. Tetrapods’ transition from land to water is a classic example of the occupation of new environments, characterized by great morphological and physiological transformations. Cetaceans and sirenians make an interesting model species to study considering their environmental changes from land to water, as well as their second radiation from marine to fluvial environments. In order to deepen our knowledge about the adaptive immune system of aquatic mammals through an evolutionary perspective considering different environmental transitions, Chapter 1 brings evolutionary analyses of the RAG1 and RAG2 genes in Cetaceans, demonstrating that RAG1 and RAG2 genes remained fairly conserved among tetrapods, and differential evolution happening in these closely linked genes in the Cetacea lineage, with RAG1 being less conserved when compared to other mammals of the phylogeny. Chapter 2 is the first characterization of both Trichechus manatus and Trichechus inunguis immunoglobulin light chain locus, showing that the number of genomically encoded segments and, consequently, the segmental diversity is limited in manatees. Manatees seem to have only a few V pseudogenes within the lambda chain organized in a different manner as seen in most tetrapods, enabling manatees to create very little antibody diversity through the immunoglobulin light chain region (AU)

• FAPESP's process: 17/14831-2 - Molecular evolution of immune system genes in aquatic mammals: identifying molecular footprints of the colonization of new environment
• Grantee: Bruna Cristina Dias
• Support Opportunities: Scholarships in Brazil - Master