Mitochondrial coding genome analysis of tropical root-knot nematodes (Meloidogyne) supports haplotype based diagnostics and reveals evidence of recent reticulate evolution

The polyphagous parthenogenetic root-knot nematodes of the genus Meloidogyne are considered to be the most significant nematode pest in sub-tropical and tropical agriculture. Despite the crucial need for correct diagnosis, identification of these pathogens remains problematic. The traditionally used diagnostic strategies, including morphometrics, host-range tests, biochemical and molecular techniques, now appear to be unreliable due to the recently-suggested hybrid origin of root-knot nematodes. In order to determine a suitable barcode region for these pathogens nine quickly-evolving mitochondrial coding genes were screened. Resulting haplotype networks revealed closely related lineages indicating a recent speciation, an anthropogenic-aided distribution through agricultural practices, and evidence for reticulate evolution within M. arenaria. Nonetheless, nucleotide polymorphisms harbor enough variation to distinguish these closely-related lineages. Furthermore, completeness of lineage sorting was verified by screening 80 populations from widespread geographical origins and variable hosts. Importantly, our results indicate that mitochondrial haplotypes are strongly linked and consistent with traditional esterase isozyme patterns, suggesting that different parthenogenetic lineages can be reliably identified using mitochondrial haplotypes. The study indicates that the barcode region Nad5 can reliably identify the major lineages of tropical root-knot nematodes.

Cloning, expression and localization of DacaCSP2 and DacaCSP3 during different reproductive stages in Daphnia carinata

Daphnia carinata are unique freshwater crustaceans that undergo both sexual and asexual reproduction, depending on environmental factors. While the molecular mechanism behind the reproductive transformation has been unknown, chemosensory proteins (CSPs) may be involved. We have cloned the cDNA sequences of two CSP genes from D. carinata using primers based on homologous sequences and rapid amplification of cDNA ends (RACE). The full-length cDNA of DacaCSP2 (GenBank accession no: KM624608) was 632 bp, with an ORF (open reading frame) of 330 bp encoding a 12.02 kDa protein; and the full-length cDNA of DacaCSP3 (GenBank accession no: KM624609) was 935 bp, with an ORF of 342 bp encoding a 12.78kDa protein. Both CSPs encoded an N-terminal signal peptide, four conserved cysteines, an OS-D superfamily domain, a 2Fe-2S ferredoxin domain, an anaphylatoxin domain and an EGF-like domain. DaCaCSP2 and DaCaCSP3 proteins were most closely related to CSPs from Daphnia pulex and were more distantly related to CSPs from other insects. Using quantitative PCR, we found expression levels of DaCaCSP2 and DaCaCSP3 mRNA were highest in sexual females, followed by parthenogenetic females, and lowest in males. The expression levels of DaCaCSP2 and DaCaCSP3 mRNA also increased at lower temperatures, which suggested they could respond to environmental cues. Whole mount in situ hybridization (ISH) showed that DaCaCSP2 and DaCaCSP3 were expressed mainly in the ovaries, summer eggs, thoracic limbs, rectum and second antennae in sexual females; while they were expressed mainly in the ovaries, thoracic limbs, rectum and second antennae in parthenogenetic females. Together, these results suggest that DacaCSP2 and DacaCSP3 may respond to environmental cues and control the reproductive switch from sexual to asexual reproduction in D. carinata.

Uncovering Cryptic Asexuality in Daphnia magna by RAD Sequencing

The breeding systems of many organisms are cryptic and difficult to investigate with observational data, yet they have profound effects on a species' ecology, evolution, and genome organization. Genomic approaches offer a novel, indirect way to investigate breeding systems, specifically by studying the transmission of genetic information from parents to offspring. Here we exemplify this method through an assessment of self-fertilization vs. automictic parthenogenesis in Daphnia magna. Self-fertilization reduces heterozygosity by 50% compared to the parents, but under automixis, whereby two haploid products from a single meiosis fuse, the expected heterozygosity reduction depends on whether the two meiotic products are separated during meiosis I or II (i.e., central vs. terminal fusion). Reviewing the existing literature and incorporating recombination interference, we derive an interchromosomal and an intrachromosomal prediction of how to distinguish various forms of automixis from self-fertilization using offspring heterozygosity data. We then test these predictions using RAD-sequencing data on presumed automictic diapause offspring of so-called nonmale producing strains and compare them with "self-fertilized" offspring produced by within-clone mating. The results unequivocally show that these offspring were produced by automixis, mostly, but not exclusively, through terminal fusion. However, the results also show that this conclusion was only possible owing to genome-wide heterozygosity data, with phenotypic data as well as data from microsatellite markers yielding inconclusive or even misleading results. Our study thus demonstrates how to use the power of genomic approaches for elucidating breeding systems, and it provides the first demonstration of automictic parthenogenesis in Daphnia.

Genetic Diversity of the Invasive Gall Wasp Leptocybe invasa (Hymenoptera: Eulophidae) and of its Rickettsia Endosymbiont, and Associated Sex-Ratio Differences

The blue-gum chalcid Leptocybe invasa Fisher & LaSalle (Hymenoptera: Eulophidae) is a gall wasp pest of Eucalyptus species, likely native to Australia. Over the past 15 years it has invaded 39 countries on all continents where eucalypts are grown. The worldwide invasion of the blue gum chalcid was attributed to a single thelytokous morphospecies formally described in 2004. Subsequently, however, males have been recorded in several countries and the sex ratio of field populations has been found to be highly variable in different areas. In order to find an explanation for such sex ratio differences, populations of L. invasa from a broad geographical area were screened for the symbionts currently known as reproductive manipulators, and both wasps and symbionts were genetically characterized using multiple genes. Molecular analyses suggested that L. invasa is in fact a complex of two cryptic species involved in the rapid and efficient spread of the wasp, the first recovered from the Mediterranean region and South America, the latter from China. All screened specimens were infected by endosymbiotic bacteria belonging to the genus Rickettsia. Two closely related Rickettsia strains were found, each infecting one of the two putative cryptic species of L. invasa and associated with different average sex ratios. Rickettsia were found to be localized in the female reproductive tissues and transovarially transmitted, suggesting a possible role of Rickettsia as the causal agent of thelytokous parthenogenesis in L. invasa. Implications for the variation of sex ratio and for the management of L. invasa are discussed.

[Characterization of retrotransposon Bov-B LINE reverse transcriptase gene sequences in parthenogenetic lizards Darevskia unisexualis and bisexual species D. nairensis and D. valentini]

Cloning and sequencing of the partial reverse transcriptase gene (750 bp) of the Bov-B LINE retrotransposon have been held in parthenogenetic lizards Darevskia unisexualis and its assumed parental bisexual species D. nairensis and D.valentini. It was shown that the percentage of transcriptionally active copies of this gene, which does not contain a stop codon, is almost the same in the three species and is about 75%. The intragenomic divergence level of these sequences is low and was found to be 2.6% in D. unisexualis, 1.9% in D. nairensis, and 1.6% in D. valentini. The phylogenetic analysis shows the distribution of copies of D. unisexualis in each of the two clusters of RT sequences characteristic of D. nairensis and D. valentini. This result supports the view of the hybrid origin of D. unisexualis and does not exclude intraspecific hybridization between D. nairensis and D. valentini.

Evolutionary dynamics of R2 retroelement and insertion inheritance in the genome of bisexual and parthenogenetic Bacillus rossius populations (Insecta Phasmida)

Theoretical and empirical studies have shown differential management of transposable elements in organisms with different reproductive strategies. To investigate this issue, we analysed the R2 retroelement structure and variability in parthenogenetic and bisexual populations of Bacillus rossius stick insects, as well as insertions inheritance in the offspring of parthenogenetic isolates and of crosses. The B. rossius genome hosts a functional (R2Br(fun) ) and a degenerate (R2Br(deg) ) element, their presence correlating with neither reproductive strategies nor population distribution. The median-joining network method indicated that R2Br(fun) duplicates through a multiple source model, while R2Br(deg) is apparently still duplicating via a master gene model. Offspring analyses showed that unisexual and bisexual offspring have a similar number of R2Br-occupied sites. Multiple or recent shifts from gonochoric to parthenogenetic reproduction may explain the observed data. Moreover, insertion frequency spectra show that higher-frequency insertions in unisexual offspring significantly outnumber those in bisexual offspring. This suggests that unisexual offspring eliminate insertions with lower efficiency. A comparison with simulated insertion frequencies shows that inherited insertions in unisexual and bisexual offspring are significantly different from the expectation. On the whole, different mechanisms of R2 elimination in unisexual vs bisexual offspring and a complex interplay between recombination effectiveness, natural selection and time can explain the observed data.

Genetic control of contagious asexuality in the pea aphid

Although evolutionary transitions from sexual to asexual reproduction are frequent in eukaryotes, the genetic bases of such shifts toward asexuality remain largely unknown. We addressed this issue in an aphid species where both sexual and obligate asexual lineages coexist in natural populations. These sexual and asexual lineages may occasionally interbreed because some asexual lineages maintain a residual production of males potentially able to mate with the females produced by sexual lineages. Hence, this species is an ideal model to study the genetic basis of the loss of sexual reproduction with quantitative genetic and population genomic approaches. Our analysis of the co-segregation of ∼ 300 molecular markers and reproductive phenotype in experimental crosses pinpointed an X-linked region controlling obligate asexuality, this state of character being recessive. A population genetic analysis (>400-marker genome scan) on wild sexual and asexual genotypes from geographically distant populations under divergent selection for reproductive strategies detected a strong signature of divergent selection in the genomic region identified by the experimental crosses. These population genetic data confirm the implication of the candidate region in the control of reproductive mode in wild populations originating from 700 km apart. Patterns of genetic differentiation along chromosomes suggest bidirectional gene flow between populations with distinct reproductive modes, supporting contagious asexuality as a prevailing route to permanent parthenogenesis in pea aphids. This genetic system provides new insights into the mechanisms of coexistence of sexual and asexual aphid lineages.

Expression of stress-related genes in the parthenogenetic forms of the pea aphid, Acyrthosiphon pisum

Aphids are an economically important group of insects that have an intricate life cycle with seasonal polyphenism. This study aimed to explore the physiological background of aphid migration from unfavorable nutritional conditions to a new, intact host plant. Specifically, the relative expression of stress/metabolism-related genes and changes in metabolic reserves were determined for the winged and wingless forms of female pea aphids, Acyrthosiphon pisum, under two different nutritional conditions. The expression level was determined for the following sets of genes: the adipokinetic hormone (AKH) and its receptor, enzymes involved in carbohydrate and lipid metabolism, detoxifying enzymes, and genes encoding exoskeleton/cuticular proteins and cytoskeleton proteins. In both forms, the transcription of the adipokinetic hormone was upregulated during nutritional stress, whereas its receptor mRNA levels remained unchanged. Similarly, the expression of genes engaged in glycogen and triglyceride degradation was elevated. Glycogen reserves and phospholipids appeared to be used during stress. In comparison, nutrient rich reproductively active females of both forms appeared to use triglycerides. Moreover, we revealed changes in the mRNA level of the detoxifying genes delta-class glutathione S-transferase (GST-δ) and cytochrome P450 monooxygenase (CYP450), as well as the CP gene (which encodes exoskeleton/cuticular proteins) and the cofilin gene (the products of which influence cytoskeleton organization). These results indicate the possible correlation between nutritional stress, energy content, AKH, and the stress-related enzymes of different metabolic pathways in winged and wingless forms of A. pisum.

Amino acid supplementation affects imprinted gene transcription patterns in parthenogenetic porcine blastocysts

To determine whether exogenous amino acids affect gene transcription patterns in parthenogenetic porcine embryos, we investigated the effects of amino acid mixtures in culture medium. Parthenogenetic embryos were cultured in PZM3 medium under four experimental conditions: 1) control (no amino acids except L-glutamine and taurine); 2) nonessential amino acids (NEAA); 3) essential amino acids (EAA); and 4) NEAA and EAA. The rate of development of embryos to the four-cell stage was not affected by treatment. However, fewer (P<0.05) embryos cultured with EAA (12.8%) reached the blastocyst stage as compared with the control group (25.6%) and NEAA group (30.3%). Based on these findings, we identified genes with altered expression in parthenogenetic embryos exposed to medium with or without EAAs. The results indicated that EAA influenced gene expression patterns, particularly those of imprinted genes (e.g., H19, IGF2R, PEG1, XIST). However, NEAAs did not affect impaired imprinted gene expressions induced by EAA. The results also showed that mechanistic target of rapamycin (MTOR) mRNA expression was significantly increased by EAA alone as compared with control cultures, and that the combined treatment with NEAA and EAA did not differ significantly from those of control cultures. Our results revealed that gene transcription levels in porcine embryos changed differentially depending on the presence of EAA or NEAA. However, the changes in the H19 mRNA observed in the parthenogenetic blastocysts expression level was not related to the DNA methylation status in the IGF2/H19 domain. The addition of exogenous amino acid mixtures affected not only early embryonic development, but also gene transcription levels, particularly those of imprinted genes. However, this study did not reveal how amino acids affect expression of imprinted genes under the culture conditions used. Further studies are thus required to fully evaluate how amino acids affect transcriptional regulation in porcine embryos.

Parthenogenesis in a whitetip reef shark Triaenodon obesus involves a reduction in ploidy

Genetic analysis of a female whitetip reef shark Triaenodon obesus and her stillborn pup, assumed to be of parthenogenetic origin, revealed that the pup was homozygous at all 24 nuclear-encoded microsatellites assayed, consistent with the idea that diploidy in the pup had been restored via terminal fusion. Flow cytometric analysis, however, indicated that the genome size of the pup was no more than half that of the mother, and microscopy revealed that nuclear volume was c. 1.73 times larger in the mother than in the pup. Together these data suggest that the pup was genetically haploid, developing directly from an unfertilized egg; as far as is known, this is the first observation of a spontaneously produced haploid vertebrate.

Karyotype characterization of in vivo- and in vitro-derived porcine parthenogenetic cell lines

Mammalian haploid cell lines provide useful tools for both genetic studies and transgenic animal production. To derive porcine haploid cells, three sets of experiments were conducted. First, genomes of blastomeres from 8-cell to 16-cell porcine parthenogenetically activated (PA) embryos were examined by chromosome spread analysis. An intact haploid genome was maintained by 48.15% of blastomeres. Based on this result, two major approaches for amplifying the haploid cell population were tested. First, embryonic stem-like (ES-like) cells were cultured from PA blastocyst stage embryos, and second, fetal fibroblasts from implanted day 30 PA fetuses were cultured. A total of six ES-like cell lines were derived from PA blastocysts. No chromosome spread with exactly 19 chromosomes (the normal haploid complement) was found. Four cell lines showed a tendency to develop to polyploidy (more than 38 chromosomes). The karyotypes of the fetal fibroblasts showed different abnormalities. Cells with 19–38 chromosomes were the predominant karyotype (59.48–60.91%). The diploid cells were the second most observed karyotype (16.17%–22.73%). Although a low percentage (3.45–8.33%) of cells with 19 chromosomes were detected in 18.52% of the fetus-derived cell lines, these cells were not authentic haploid cells since they exhibited random losses or gains of some chromosomes. The haploid fibroblasts were not efficiently enriched via flow cytometry sorting. On the contrary, the diploid cells were efficiently enriched. The enriched parthenogenetic diploid cells showed normal karyotypes and expressed paternally imprinted genes at extremely low levels. We concluded that only a limited number of authentic haploid cells could be obtained from porcine cleavage-stage parthenogenetic embryos. Unlike mouse, the karyotype of porcine PA embryo-derived haploid cells is not stable, long-term culture of parthenogenetic embryos, either in vivo or in vitro, resulted in abnormal karyotypes. The porcine PA embryo-derived diploid fibroblasts enriched from sorting might be candidate cells for paternally imprinted gene research.

Dickkopf-related protein 1 inhibits the WNT signaling pathway and improves pig oocyte maturation

The ability to mature oocytes in vitro provides a tool for creating embryos by parthenogenesis, fertilization, and cloning. Unfortunately the quality of oocytes matured in vitro falls behind that of in vivo matured oocytes. To address this difference, transcriptional profiling by deep sequencing was conducted on pig oocytes that were either matured in vitro or in vivo. Alignment of over 18 million reads identified 1,316 transcripts that were differentially represented. One pathway that was overrepresented in the oocytes matured in vitro was for Wingless-type MMTV integration site (WNT) signaling. In an attempt to inhibit the WNT pathway, Dickkopf-related protein 1 was added to the in vitro maturation medium. Addition of Dickkopf-related protein 1 improved the percentage of oocytes that matured to the metaphase II stage, increased the number of nuclei in the resulting blastocyst stage embryos, and reduced the amount of disheveled segment polarity protein 1 protein in oocytes. It is concluded that transcriptional profiling is a powerful method for detecting differences between in vitro and in vivo matured oocytes, and that the WNT signaling pathway is important for proper oocyte maturation.

Characterization of the altered gene expression profile in early porcine embryos generated from parthenogenesis and somatic cell chromatin transfer

The in vitro production of early porcine embryos is of particular scientific and economic interest. In general, embryos produced from in vitro Assisted Reproductive Technologies (ART) manipulations, such as somatic cell chromatin transfer (CT) and parthenogenetic activation (PA), are less developmentally competent than in vivo–derived embryos. The mechanisms underlying the deficiencies of embryos generated from PA and CT have not been completely understood. To characterize the altered genes and gene networks in embryos generated from CT and PA, comparative transcriptomic analyses of in vivo (IVV) expanded blastocysts (XB), IVV hatched blastocyst (HB), PA XB, PA HB, and CT HB were performed using a custom microarray platform enriched for genes expressed during early embryonic development. Differential expressions of 1492 and 103 genes were identified in PA and CT HB, respectively, in comparison with IVV HB. The “eIF2 signalling”, “mitochondrial dysfunction”, “regulation of eIF4 and p70S6K signalling”, “protein ubiquitination”, and “mTOR signalling” pathways were down-regulated in PA HB. Dysregulation of notch signalling–associated genes were observed in both PA and CT HB. TP53 was predicted to be activated in both PA and CT HB, as 136 and 23 regulation targets of TP53 showed significant differential expression in PA and CT HB, respectively, in comparison with IVV HB. In addition, dysregulations of several critical pluripotency, trophoblast development, and implantation-associated genes (NANOG, GATA2, KRT8, LGMN, and DPP4) were observed in PA HB during the blastocyst hatching process. The critical genes that were observed to be dysregulated in CT and PA embryos could be indicative of underlying developmental deficiencies of embryos produced from these technologies.

Concise review: parthenote stem cells for regenerative medicine: genetic, epigenetic, and developmental features

Embryonic stem cells (ESCs) have the potential to provide unlimited cells and tissues for regenerative medicine. ESCs derived from fertilized embryos, however, will most likely be rejected by a patient's immune system unless appropriately immunomatched. Pluripotent stem cells (PSCs) genetically identical to a patient can now be established by reprogramming of somatic cells. However, practical applications of PSCs for personalized therapies are projected to be unfeasible because of the enormous cost and time required to produce clinical-grade cells for each patient. ESCs derived from parthenogenetic embryos (pESCs) that are homozygous for human leukocyte antigens may serve as an attractive alternative for immunomatched therapies for a large population of patients. In this study, we describe the biology and genetic nature of mammalian parthenogenesis and review potential advantages and limitations of pESCs for cell-based therapies.

Chromosomes in the porcine first polar body possess competence of second meiotic division within enucleated MII stage oocytes

To determine whether chromosomes in the porcine first polar body (PB1) can complete the second meiotic division and subsequently undergo normal pre-implantation embryonic development, we examined the developmental competence of PB1 chromosomes injected into enucleated MII stage oocytes by nuclear transfer method (chromosome replacement group, CR group). After parthenogenetic activation (PA) or in vitro fertilization (IVF), the cleavage rate of reconstructed oocytes in the IVF group (CR-IVF group, 36.4 ± 3.2%) and PA group (CR-PA group, 50.8 ± 4.2%) were significantly lower than that of control groups in which normal MII oocytes were subjected to IVF (MII-IVF group, 75.8 ± 1.5%) and PA (MII-PA group, 86.9 ± 3.7%). Unfertilized rates was significantly higher in the CR-IVF group (48.6 ± 3.3%) than in the MII-IVF group (13.1 ± 3.4%). The blastocyst formation rate was 8.3 ± 1.9% in the CR-PA group, whereas no blastocyst formation was observed in the CR-IVF group. To produce tetraploid parthenogenetic embryos, intact MII stage oocytes injected with PB1 chromosomes were electrically stimulated, treated with 7.5 μg/mL cytochalasin B for 3 h (MII oocyte + PB1 + CB group), and then cultured without cytochalasin B. The average cleavage rate of reconstructed oocytes was 72.5% (48 of 66), and the blastocyst formation rate was 18.7% (9 of 48). Chromosome analysis showed similar proportions of haploid and diploid cells in the control (normal MII oocytes) and CR groups after PA; overall, 23.6% of blastocysts were tetraploid in the MII oocyte + PB1 + CB group. These results demonstrate that chromosomes in PB1 can participate in normal pre-implantation embryonic development when injected into enucleated MII stage oocytes, and that tetraploid PA blastocysts are produced (although at a low proportion) when PB1 chromosomes are injected into intact MII stage oocytes.

The imprinted polycomb group gene Sfmbt2 is required for trophoblast maintenance and placenta development

Imprinted genes play important roles in placenta development and function. Parthenogenetic embryos, deficient in paternally expressed imprinted genes, lack extra-embryonic tissues of the trophoblast lineage. Parthenogenetic trophoblast stem cells (TSCs) are extremely difficult to derive, suggesting that an imprinted gene(s) is necessary for TSC establishment or maintenance. In a candidate study, we were able to narrow the list to one known paternally expressed gene, Sfmbt2. We show that mouse embryos inheriting a paternal Sfmbt2 gene trap null allele have severely reduced placentae and die before E12.5 due to reduction of all trophoblast cell types. We infected early embryos with lentivirus vectors expressing anti-Sfmbt2 shRNAs and found that TSC derivation was significantly reduced. Together, these observations support the hypothesis that loss of SFMBT2 results in defects in maintenance of trophoblast cell types necessary for development of the extra-embryonic tissues, the placenta in particular.

Mitochondrial DNA suggests a single maternal origin for the widespread triploid parthenogenetic pest species, Paratanytarsus grimmii, but microsatellite variation shows local endemism

Parthenogenesis is common among invasive pest species, with many parthenogenetic species also showing polyploidy. Parthenogenetic polyploid species often have multiple hybrid origins and the potential to rapidly spread over vast geographical areas. In this study, we examine patterns of mitochondrial and microsatellite variation in a widespread triploid parthenogenetic chironomid pest species, Paratanytarsus grimmii. Based on samples from five countries, including Australia, England, Germany, Japan, and Canada, we found extremely low mitochondrial diversity (<0.14%), with most individuals sharing a common and widespread haplotype. In contrast, microsatellite diversity revealed 41 clonal variants, which were regionally endemic. These findings suggest a single invasive maternal lineage of P. grimmii is likely to have recently spread over a broad geographical range. High levels of genotypic endemism suggest P. grimmii populations have remained relatively isolated after an initial spread, with little ongoing migration. This, in part, can be attributed to rapid genetic differentiation via mutations of common clonal genotypes after P. grimmii spread, but multiple polyploidization and subsequent founder events are also likely to be contributing factors.

Inventory and phylogenetic analysis of meiotic genes in monogonont rotifers

A long-standing question in evolutionary biology is how sexual reproduction has persisted in eukaryotic lineages. As cyclical parthenogens, monogonont rotifers are a powerful model for examining this question, yet the molecular nature of sexual reproduction in this lineage is currently understudied. To examine genes involved in meiosis, we generated partial genome assemblies for 2 distantly related monogonont species, Brachionus calyciflorus and B. manjavacas. Here we present an inventory of 89 meiotic genes, of which 80 homologs were identified and annotated from these assemblies. Using phylogenetic analysis, we show that several meiotic genes have undergone relatively recent duplication events that appear to be specific to the monogonont lineage. Further, we compare the expression of "meiosis-specific" genes involved in recombination and all annotated copies of the cell cycle regulatory gene CDC20 between obligate parthenogenetic (OP) and cyclical parthenogenetic (CP) strains of B. calyciflorus. We show that "meiosis-specific" genes are expressed in both CP and OP strains, whereas the expression of one of the CDC20 genes is specific to cyclical parthenogenesis. The data presented here provide insights into mechanisms of cyclical parthenogenesis and establish expectations for studies of obligate asexual relatives of monogononts, the bdelloid rotifer lineage.

[Intra- and interspecific polymorphism of (AAT)n in microsatellite locus du47D in parthenogenetic species of the genus Darevskia]

The molecular structure of the allelic variants of (AAT)n of the Du47D microsatellite locus was determined in parthenogenetic lizards Darevskia dahli, D. armeniaca, and D. rostombekovi. Comparative analysis of these alleles showed that they were characterized by perfect structure of microsatellite cluster, and were different in the number of (AAT) monomeric units, as well as in the combinations of species-specific substitutions and deletions in the microsatellite flanking regions. Molecular structure of microsatellite cluster, species-specific single nucleotide polymorphism (SNP), and different representation of alleles Du47 in the samples of parthenogenetic species examined point to the origin of the alleles from different bisexual species, which is consistent with the hybrid nature of unisexual species of the genus Darevskia. In addition, these data reflect different combination patterns of interspecific hybridization events with the participation of the same bisexual species upon the formation of hybrid genomes of parthenogenetic species. Possible application of the allelic variants of microsatellite loci of parthenogenetic lizards as the genetic markers for the analysis of the genomes of parthenogenetic species in the light of evolution, ecology, and parthenogenetic type of reproduction in vertebrates is discussed.

Genetic positioning of centromeres through half-tetrad analysis in gynogenetic diploid families of the Zhikong scallop (Chlamys farreri)

Centromere mapping is a powerful tool for improving linkage maps, investigating crossover events, and understanding chiasma interference during meiosis. Ninety microsatellite markers selected across all linkage groups (LGs) from a previous Chlamys farreri genetic map were studied in three artificially induced meiogynogenetic families for centromere mapping by half-tetrad analysis. Inheritance analyses showed that all 90 microsatellite loci conformed to Mendelian inheritance in the control crosses, while 4.4 % of the microsatellite loci showed segregation departures from an expected 1:1 ratio of two homozygote classes in meiogynogenetic progeny. The second division segregation frequency (y) of the microsatellites ranged from 0.033 to 0.778 with a mean of 0.332, confirming the occurrence of partial chiasma interference in this species. Heterogeneity of y is observed in one of 42 cases in which markers were typed in more than one family, suggesting variation in gene-centromere recombination among families. Centromere location was mostly in accordance with the C. farreri karyotype, but differences in marker order between linkage and centromere maps occurred. Overall, this study makes the genetic linkage map a more complete and informative tool for genomic studies and it will also facilitate future research of the structure and function of the scallop centromeres.

[Line class retroposon is the component of the DNA polymorphic fragments pattern of trematode Himasthla elongata parthenitae]

We have determined that S-SAP method (Sequence specific amplification polymorphism) reveals clonal variability in the genomes of larvae of flatworm Himasthla elongata (Trematoda, Echinostomatidae). Being parthenogenetic the larvae were previously considered to be genetically homogeneous. Cloning and sequencing of a -500 bp conservative fragment (B1) from the fragments' pattern has been performed. Sequence analysis of B1 has shown that this fragment has maximum homology with LINE elements from CR1 family of Hydra and sparrow. In situ hybridization (FISH) has detected dispersed distribution of B1. Several other fragments cloned from the same lane of agarose electrophoresis correspond to conservative domain of reverse transcriptase (RT) from CR1 family. Thus, we have shown that 1) cercariae of trematode H. elongata have clonal variability; 2) the S-SAP method allows to obtaining patterns of fragment distribution characteristic of individual cercariae; 3) conservative domain of RT of CR1 family participates in the pattern of polymorphic fragments generation. Identification of the CR1 transcripts in cercariae of H. elongata transcriptome is the aim of the future work. Cloning of the variable fragments from the fragments' pattern is in progress.

Characterization of the procera tomato mutant shows novel functions of the SlDELLA protein in the control of flower morphology, cell division and expansion, and the auxin-signaling pathway during fruit-set and development

procera (pro) is a tall tomato (Solanum lycopersicum) mutant carrying a point mutation in the GRAS region of the gene encoding SlDELLA, a repressor in the gibberellin (GA) signaling pathway. Consistent with the SlDELLA loss of function, pro plants display a GA-constitutive response phenotype, mimicking wild-type plants treated with GA₃. The ovaries from both nonemasculated and emasculated pro flowers had very strong parthenocarpic capacity, associated with enhanced growth of preanthesis ovaries due to more and larger cells. pro parthenocarpy is facultative because seeded fruits were obtained by manual pollination. Most pro pistils had exserted stigmas, thus preventing self-pollination, similar to wild-type pistils treated with GA₃ or auxins. However, Style2.1, a gene responsible for long styles in noncultivated tomato, may not control the enhanced style elongation of pro pistils, because its expression was not higher in pro styles and did not increase upon GA₃ application. Interestingly, a high percentage of pro flowers had meristic alterations, with one additional petal, sepal, stamen, and carpel at each of the four whorls, respectively, thus unveiling a role of SlDELLA in flower organ development. Microarray analysis showed significant changes in the transcriptome of preanthesis pro ovaries compared with the wild type, indicating that the molecular mechanism underlying the parthenocarpic capacity of pro is complex and that it is mainly associated with changes in the expression of genes involved in GA and auxin pathways. Interestingly, it was found that GA activity modulates the expression of cell division and expansion genes and an auxin signaling gene (tomato AUXIN RESPONSE FACTOR7) during fruit-set.

The significance of sex

Sexual and asexual modes of proliferation are associated with advantages and disadvantages, yet a profound percept that would account for both ways of reproduction is missing. On the basis of the 2nd law of thermodynamics we find that both sexual and asexual reproduction can be regarded as a means to consume free energy in least time. Parthenogenesis is a fast way to consume a rich repository of free energy, e.g., an ample stock of food with a large number of individuals, whereas sexual reproduction is a fast way to consume diverse and dispersed resources with a large variety of individuals. Most organisms have adapted to their surroundings accordingly and some organisms switch from one mode of reproduction to the other depending on the amount and dispersion of free-energy sources. We conclude that the least-time free energy consumption in respective surroundings, as the general criterion of natural selection, determines also sexual and asexual modes of reproduction.