USING HAP2 FOR IDENTIFICATION OF GAMETE FUSOGENS

GUDIÑO, VIRGINIA; AGUILAR, PABLO S.

VIRTUAL

Congreso; LVII SAIB Annual Meeting - XVI SAMIGE Meeting (virtual); 2021

SAIB-SAMIGE

The fusion of the biological membranes is not spontaneous. Specific proteins, called fusogens, catalyze this fusion in a precise way and under strict spatial and temporal control. In contrast to enveloped virus fusion and intracellular fusion, the fusogensthat catalyze cell fusion are hardly known. In this sense, different research work shows that the HAP2/GCS1 protein is involved in the fusion of gametes of organisms as diverse as: Arabidopsis thaliana, Chlamydomonas reinhardtii, Tetrahymenathermophila, Plasmodium falciparum and Dictyostelium discoideum (Speijer et al. 2015, doi: 10.1073/pnas.1501725112). In collaboration with others, our group showed that A. thaliana HAP2 (AtHAP2) is enough to promote cell-cell fusion. Thispositions this protein as a true cell fusogen. Through phylogenetic and structural studies of HAP2, somatic cell fusogens (FFs) and class II viral fusogens we found out that these proteins share common ancestry (Valansi et al. 2017, doi:10.1083/jcb.201610093). Furthermore, they are all involved in membrane fusion processes in the extracellular environment. Accordingly, we call this superfamily FUSEXINS (FUSion proteins essential for Sexual reproduction and EXoplasmic merger of plasma membranes). Fusexins are ancestral and, therefore, they are present in most eukaryotic lineages. However, they have not been detected in fungal and vertebrate genomes yet. The aim of this study is to identify and characterize candidate genes to participate in the gamete fusion reaction in humans and other species of interest. In this way, the purpose of this research is to contribute to the understanding of a basic life process such as fertilization. In this work, the mating of yeast Saccharomyces cerevisiae is the gamete fusion model used for the identification and characterization of cellular fusogens. Differentinvestigations support a model in which the integral plasma membrane protein Prm1 controls the fusion mechanism to prevent cell lysis. In the absence of extracellular calcium and Prm1, the cell fusion reaction is deregulated. This leads to a decrease incell fusion efficiency and to cell lysis as a by-product. This work uses this phenotype of prm1 mutants to evaluate whether AtHAP2 can complement its fusion defect. If it can complement, we will be able to carry out a genetic screening to search formutants that are incapable of forming diploids and that are only complemented by AtHAP2. The genes affected in these mutants will be considered as candidate genes involved in cell fusion. In addition, the high conservation observed between HAP2, viral fusogens and FFs, suggest that it is possible that this research contributes to understanding mechanisms involved in viral invasion and in tissue development dependent on cell-cell fusion.