A Surface Glycoprotein Indispensable for Gamete Fusion in the Social Amoeba Dictyostelium discoideum

Abstract

bSexual reproduction is essential for the maintenance of species in a wide variety of multicellular organisms, and even unicellular organisms that normally proliferate asexually possess a sexual cycle because of its contribution to increased genetic diversity. Information concerning the molecules involved in fertilization is accumulating for many species of the metazoan, plant, and fungal lineages, and the evolutionary consideration of sexual reproduction systems is now an interesting issue. Macrocyst formation in the social amoeba Dictyostelium discoideum is a sexual process in which cells become sexually mature under dark and submerged conditions and fuse with complementary mating-type cells. In the present study, we isolated D. discoideum insertional mutants defective in sexual cell fusion and identified the relevant gene, macA, which encodes a highly glycosylated, 2,041-amino-acid membrane protein (MacA). Although its overall similarity is restricted to proteins of unknown function within dictyostelids, it contains LamGL and discoidin domains, which are implicated in cell adhesion. The growth and development of macA-null mutants were indistinguishable from those of the parental strain. The overexpression of macA using the V18 promoter in a macA-null mutant completely restored its sexual defects. Although the macA gene encoded exactly the same protein in a complementary mating-type strain, it was expressed at a much lower level. These results suggest that MacA is indispensable for gamete interactions in D. discoideum, probably via cell adhesion. There is a possibility that it is controlled in a mating-typedependent manner.

Stepwise Evolution of Coral Biomineralization Revealed with Genome-Wide Proteomics and Transcriptomics

“…Briefly, peptide digests were analyzed using a capillary liquid chromatography system (Ultima3000; DIONEX) connected online to a mass spectrometer (LTQ-XL, Thermo Scientific). Raw spectra were processed using SEQUEST software to extract peak lists [ 38 ]. Resulting peak lists were analyzed using an in-house MASCOT (ver.…”

Two HAP2-GCS1 homologs responsible for gamete interactions in the cellular slime mold with multiple mating types: Implication for common mechanisms of sexual reproduction shared by plants and protozoa and for male-female differentiation

“…A disruption construct was made by sequential fusion PCR ( Kuwayama et al, 2002 ); the left and right arms were first amplified using genomic DNA as a template and the specific primer sets shown in Table S1 , and the fragments were connected to the left and right of the bsR cassette composed of the act 15 promoter, bsr gene, and act8 terminator. An over-expression vector was constructed by inserting a cDNA between the v18 promoter and act8 terminator of pTMV18 ( Araki et al, 2012 ).…”

“…To date, the molecular functions of the genes are undetermined. In addition to these genes, cell surface glycoprotein, MacA, coded by macA gene, is indispensable for sexual cell interactions in D. discoideum ( Araki et al, 2012 ). This protein is unique to the dictyostelid lineage and its evolutionary relationship to proteins of other organisms could not be traced.…”

“…This protein is unique to the dictyostelid lineage and its evolutionary relationship to proteins of other organisms could not be traced. Since the structure and expression of both macA and matA genes were unaltered in cell fusion-defective type-I mutants, we inferred that a third gene is involved in gamete interactions ( Araki et al, 2012 ). A homolog of the HAP2-GCS1 gene was a candidate based on its role in gamete fusion in wide-ranging taxa.…”

Sex and macrocyst formation in Dictyostelium

“…Another membrane protein named MacA that is unrelated to HAP2-GCS1, also functions during gamete fusion in D. discoideum and may be important for cell-cell interactions prior to fusion (Araki et al, 2012). In the homothallic DM7 isolate, which is related to D. clavatum and D. longosporum (Mohri et al, 2018) ethylene promotes zygote formation, likely helping to trigger gamete fusion (Amagai, 1989).…”