Genetics and Epigenetics of Mating Type Determination in Paramecium and Tetrahymena

• Published in: Annual review of microbiology Vol. 71; no. 1; pp. 133 - 156
• Main Authors: Orias, Eduardo, Singh, Deepankar Pratap, Meyer, Eric
• Format: Journal Article
• Language: English
• Published: United States Annual Reviews 08-09-2017; Annual Reviews, Inc
• Subjects: Biological evolution; Ciliates; Deoxyribonucleic acid; Differentiation; DNA; DNA, Protozoan - genetics; Epigenetics; Epigenomics; Genetics; Genomes; Heredity; Inbreeding; inbreeding outbreeding balance; Incompatibility; Mating; Mating types; Membrane proteins; nuclear differentiation; Nuclei; Outbreeding; Paramecium; Paramecium - genetics; Paramecium - growth & development; programmed genome editing; Proteins; Protozoa; Recombination; self nonself recognition; Self-incompatibility; sexual reorganization; Stochasticity; Tetrahymena; Tetrahymena - genetics; Tetrahymena - growth & development; transmembrane proteins; self/nonself recognition; transmembrane proteins; programmed genome editing; inbreeding/outbreeding balance; nuclear differentiation; sexual reorganization
• ISSN: 0066-4227; 1545-3251
• DOI: 10.1146/annurev-micro-090816-093342

While sex is an ancient and highly conserved eukaryotic invention, self-incompatibility systems such as mating types or sexes appear to be derived limitations that show considerable evolutionary plasticity. Within a single class of ciliates,
Paramecium
and
Tetrahymena
species have long been known to present a wide variety of mating type numbers and modes of inheritance, but only recently have the genes involved been identified. Although similar transmembrane proteins mediate self nonself recognition in both ciliates, the mechanisms of mating type determination differ widely, ranging from Mendelian systems to developmental nuclear differentiation, either stochastic or maternally inherited. The non-Mendelian systems rely on programmed editing of the germline genome that occurs during differentiation of the somatic nucleus, and they have co-opted different DNA recombination mechanisms-some previously unknown. Here we review the recent molecular advances and some remaining unsolved questions and discuss the possible implications of these diverse mechanisms for inbreeding outbreeding balance regulation.