E. Przybos

Genome-defence small RNAs exapted for epigenetic mating-type inheritance

In the ciliate Paramecium, transposable elements and their single-copy remnants are deleted during the development of somatic macronuclei from germline micronuclei, at each sexual generation. Deletions are targeted by scnRNAs, small RNAs produced from the germ line during meiosis that first scan the maternal macronuclear genome to identify missing sequences, and then allow the zygotic macronucleus to reproduce the same deletions. Here we show that this process accounts for the maternal inheritance of mating types in Paramecium tetraurelia, a long-standing problem in epigenetics. Mating type E depends on expression of the transmembrane protein mtA, and the default type O is determined during development by scnRNA-dependent excision of the mtA promoter. In the sibling species Paramecium septaurelia, mating type O is determined by coding-sequence deletions in a different gene, mtB, which is specifically required for mtA expression. These independently evolved mechanisms suggest frequent exaptation of the scnRNA pathway to regulate cellular genes and mediate transgenerational epigenetic inheritance of essential phenotypic polymorphisms.

Genetic analysis of the Paramecium aurelia species complex (Protozoa: Ciliophora) by classical and molecular methods

Abstract The Paramecium aurelia complex includes 15 species (sibling species) and is characterised by inbreeding (to varying degrees in different species), causing an increase in intra‐specific differentiation. Investigations into inter‐ and intraspecific differentiation of strains originating from remote habitats within species of the complex were carried out by classical inter‐strain crosses and molecular analyses (RAPD‐PCR fingerprints, ARDRA riboprints, RFLP‐PCR analysis). RAPD analysis showed that all species in the complex possessed characteristic band patterns and the majority were also polymorphic intra‐specifically. A correlation exists between the degree of inbreeding characteristic for a species with differentiation of DNAgenotypes revealed by RAPD analysis within species, where inbreeders showed substantial variability of band patterns and moderate inbreeders were highly similar. RFLP analysis (a 480bp fragment of the gene coding the Hsp 70 protein) with the application of restriction enzyme TruII distinguished among species, while digestion with restriction enzyme AluI distinguished groups of species (clusters) and both enzymes revealed intra‐species polymorphism within P. dodecaurelia. ARDRA riboprinting (using a fragment of SSU‐LSU rDNA, about 2400 bp) with restriction enzymes HhaI, AluI, HinfI, TaqI distinguished groups of species with different band patterns. The majority of enzymes also demonstrated intra‐specific differentiation within P. dodecaurelia. TaqI also revealed intraspecific differences in P. biaurelia and P. tetraurelia. All species in the P. aurelia complex showed a high percentage of surviving hybrid clones in F 1 obtained by conjugation and F2 obtained by autogamy in inter‐strain crosses. A low percentage was observed only in F2 inter‐strain hybrids of P. tredecaurelia, however no cytological changes in the nuclear apparatuses were detected and similar band patterns existed in the studied strains. Future studies, including sequencing of rDNA fragments, may disclose deeper relationships of the species.

Distribution of the Paramecium aurelia Species Complex (Protozoa, Ciliophora) in the Carpathian Chain of Poland*

Four species of the Paramecium aurelia complex were found in the Carpathian chain: P. primaurelia, P. biaurelia, P. tetraurelia and P. novaurelia. However, variation in the frequency of settlement of these species in the region was observed; P. biaurelia and P. novaurelia appeared with the greatest frequency, P. Primaurelia occurred less frequently. while P. tetraurelia was rather rare being found only in the Tatras.

Species of the Paramecium aurelia complex (Protozoa, Ciliophora) in the Middle Sudetes of Poland

Four species of the Paramecium aurelia complex were found in the studied territory (Klodzko Basin) of the Middle Sudetes in Poland, i.e. Paramecium primaurelia, P. biaurelia, P. tetraurelia and P. novaurelia. Of these, P. biaurelia and P. novaurelia appeared with greater frequency than P. primaurelia. Both species dominated over P. primaurelia in the number of determined habitats, as well as in the number of examined clones. Paramecium tetraurelia was rare in the area, being found in only one habitat.

Paramecium tredecaurelia: A Unique Non-Polymorphic Species of the P. aurelia spp. Complex (Oligohymenophorea, Ciliophora)

New stands of Paramecium tredecaurelia , a rare species of the P. aurelia spp. complex, were identified in Thailand and Madagascar on the basis of mating reactions and molecular markers (rDNA and mtDNA). Analysis of DNA fragments showed that all P. tredecaurelia strains, the recently recorded ones and the ones known previously from France, Mexico, and Israel, form a monophyletic and well-defined clade in the P. aurelia species trees. All of these strains, collected from different localities around the world, represent identical or nearly identical haplotypes in terms of all the studied DNA fragments. Given the huge distances between particular collection sites, such a low level of variability of the studied sequences may result from a slow rate of evolution in P. tredecaurelia .