Mosquito transposable elements

Proteomics informed by transcriptomics for characterising active transposable elements and genome annotation in Aedes aegypti

BACKGROUND

Aedes aegypti is a vector for the (re-)emerging human pathogens dengue, chikungunya, yellow fever and Zika viruses. Almost half of the Ae. aegypti genome is comprised of transposable elements (TEs). Transposons have been linked to diverse cellular processes, including the establishment of viral persistence in insects, an essential step in the transmission of vector-borne viruses. However, up until now it has not been possible to study the overall proteome derived from an organism's mobile genetic elements, partly due to the highly divergent nature of TEs. Furthermore, as for many non-model organisms, incomplete genome annotation has hampered proteomic studies on Ae. aegypti.

RESULTS

We analysed the Ae. aegypti proteome using our new proteomics informed by transcriptomics (PIT) technique, which bypasses the need for genome annotation by identifying proteins through matched transcriptomic (rather than genomic) data. Our data vastly increase the number of experimentally confirmed Ae. aegypti proteins. The PIT analysis also identified hotspots of incomplete genome annotation, and showed that poor sequence and assembly quality do not explain all annotation gaps. Finally, in a proof-of-principle study, we developed criteria for the characterisation of proteomically active TEs. Protein expression did not correlate with a TE's genomic abundance at different levels of classification. Most notably, long terminal repeat (LTR) retrotransposons were markedly enriched compared to other elements. PIT was superior to 'conventional' proteomic approaches in both our transposon and genome annotation analyses.

CONCLUSIONS

We present the first proteomic characterisation of an organism's repertoire of mobile genetic elements, which will open new avenues of research into the function of transposon proteins in health and disease. Furthermore, our study provides a proof-of-concept that PIT can be used to evaluate a genome's annotation to guide annotation efforts which has the potential to improve the efficiency of annotation projects in non-model organisms. PIT therefore represents a valuable new tool to study the biology of the important vector species Ae. aegypti, including its role in transmitting emerging viruses of global public health concern.

Proteomics informed by transcriptomics for characterising active transposable elements and genome annotation in Aedes aegypti

BACKGROUND

Aedes aegypti is a vector for the (re-)emerging human pathogens dengue, chikungunya, yellow fever and Zika viruses. Almost half of the Ae. aegypti genome is comprised of transposable elements (TEs). Transposons have been linked to diverse cellular processes, including the establishment of viral persistence in insects, an essential step in the transmission of vector-borne viruses. However, up until now it has not been possible to study the overall proteome derived from an organism's mobile genetic elements, partly due to the highly divergent nature of TEs. Furthermore, as for many non-model organisms, incomplete genome annotation has hampered proteomic studies on Ae. aegypti.

RESULTS

We analysed the Ae. aegypti proteome using our new proteomics informed by transcriptomics (PIT) technique, which bypasses the need for genome annotation by identifying proteins through matched transcriptomic (rather than genomic) data. Our data vastly increase the number of experimentally confirmed Ae. aegypti proteins. The PIT analysis also identified hotspots of incomplete genome annotation, and showed that poor sequence and assembly quality do not explain all annotation gaps. Finally, in a proof-of-principle study, we developed criteria for the characterisation of proteomically active TEs. Protein expression did not correlate with a TE's genomic abundance at different levels of classification. Most notably, long terminal repeat (LTR) retrotransposons were markedly enriched compared to other elements. PIT was superior to 'conventional' proteomic approaches in both our transposon and genome annotation analyses.

CONCLUSIONS

We present the first proteomic characterisation of an organism's repertoire of mobile genetic elements, which will open new avenues of research into the function of transposon proteins in health and disease. Furthermore, our study provides a proof-of-concept that PIT can be used to evaluate a genome's annotation to guide annotation efforts which has the potential to improve the efficiency of annotation projects in non-model organisms. PIT therefore represents a valuable new tool to study the biology of the important vector species Ae. aegypti, including its role in transmitting emerging viruses of global public health concern.

Proteomics informed by transcriptomics for characterising active transposable elements and genome annotation in Aedes aegypti

BACKGROUND

Aedes aegypti is a vector for the (re-)emerging human pathogens dengue, chikungunya, yellow fever and Zika viruses. Almost half of the Ae. aegypti genome is comprised of transposable elements (TEs). Transposons have been linked to diverse cellular processes, including the establishment of viral persistence in insects, an essential step in the transmission of vector-borne viruses. However, up until now it has not been possible to study the overall proteome derived from an organism's mobile genetic elements, partly due to the highly divergent nature of TEs. Furthermore, as for many non-model organisms, incomplete genome annotation has hampered proteomic studies on Ae. aegypti.

RESULTS

We analysed the Ae. aegypti proteome using our new proteomics informed by transcriptomics (PIT) technique, which bypasses the need for genome annotation by identifying proteins through matched transcriptomic (rather than genomic) data. Our data vastly increase the number of experimentally confirmed Ae. aegypti proteins. The PIT analysis also identified hotspots of incomplete genome annotation, and showed that poor sequence and assembly quality do not explain all annotation gaps. Finally, in a proof-of-principle study, we developed criteria for the characterisation of proteomically active TEs. Protein expression did not correlate with a TE's genomic abundance at different levels of classification. Most notably, long terminal repeat (LTR) retrotransposons were markedly enriched compared to other elements. PIT was superior to 'conventional' proteomic approaches in both our transposon and genome annotation analyses.

CONCLUSIONS

We present the first proteomic characterisation of an organism's repertoire of mobile genetic elements, which will open new avenues of research into the function of transposon proteins in health and disease. Furthermore, our study provides a proof-of-concept that PIT can be used to evaluate a genome's annotation to guide annotation efforts which has the potential to improve the efficiency of annotation projects in non-model organisms. PIT therefore represents a valuable new tool to study the biology of the important vector species Ae. aegypti, including its role in transmitting emerging viruses of global public health concern.

Evolvability, epigenetics and transposable elements

Evolvability can be defined as the capacity of an individual to evolve and thus to capture adaptive mutations. Transposable elements (TE) are an important source of mutations in organisms. Their capacity to transpose within a genome, sometimes at a high rate, and their copy number regulation are environment-sensitive, as are the epigenetic pathways that mediate TE regulation in a genome. In this review we revisit the way we see evolvability with regard to transposable elements and epigenetics.

A cis-regulatory sequence driving metabolic insecticide resistance in mosquitoes: functional characterisation and signatures of selection

Although cytochrome P450 (CYP450) enzymes are frequently up-regulated in mosquitoes resistant to insecticides, no regulatory motifs driving these expression differences with relevance to wild populations have been identified. Transposable elements (TEs) are often enriched upstream of those CYP450s involved in insecticide resistance, leading to the assumption that they contribute regulatory motifs that directly underlie the resistance phenotype. A partial CuRE1 (Culex Repetitive Element 1) transposable element is found directly upstream of CYP9M10, a cytochrome P450 implicated previously in larval resistance to permethrin in the ISOP450 strain of Culex quinquefasciatus, but is absent from the equivalent genomic region of a susceptible strain. Via expression of CYP9M10 in Escherichia coli we have now demonstrated time- and NADPH-dependant permethrin metabolism, prerequisites for confirmation of a role in metabolic resistance, and through qPCR shown that CYP9M10 is >20-fold over-expressed in ISOP450 compared to a susceptible strain. In a fluorescent reporter assay the region upstream of CYP9M10 from ISOP450 drove 10× expression compared to the equivalent region (lacking CuRE1) from the susceptible strain. Close correspondence with the gene expression fold-change implicates the upstream region including CuRE1 as a cis-regulatory element involved in resistance. Only a single CuRE1 bearing allele, identical to the CuRE1 bearing allele in the resistant strain, is found throughout Sub-Saharan Africa, in contrast to the diversity encountered in non-CuRE1 alleles. This suggests a single origin and subsequent spread due to selective advantage. CuRE1 is detectable using a simple diagnostic. When applied to C. quinquefasciatus larvae from Ghana we have demonstrated a significant association with permethrin resistance in multiple field sites (mean Odds Ratio = 3.86) suggesting this marker has relevance to natural populations of vector mosquitoes. However, when CuRE1 was excised from the allele used in the reporter assay through fusion PCR, expression was unaffected, indicating that the TE has no direct role in resistance and hence that CuRE1 is acting only as a marker of an as yet unidentified regulatory motif in the association analysis. This suggests that a re-evaluation of the assumption that TEs contribute regulatory motifs involved in gene expression may be necessary.

ATon, abundant novel nonautonomous mobile genetic elements in yellow fever mosquito (Aedes aegypti)

Background

Mosquitoes are important pathogen vectors affecting human and other animals. Studies on genetic control of mosquito mediated disease transmission gained traction recently due to mosquito transgenesis technology. Active transposons are considered valuable tools to propagate pathogen resistance transgenes among mosquitoes, rendering the whole population recalcitrant to diseases. A major hurdle in this approach is the inefficient remobilization activity after the integration of heterologous transposon vectors bearing transgenes into chromosomes. Therefore, endogenous active transposons in mosquito genomes are highly desirable.

Results

Starting with the transposable element database of the yellow fever mosquito Aedes aegypti genome, detailed analyses of the members of each TE family were performed to identify sequences with multiple identical copies, an indicator of their latest or current transposition activity. Among a dozen of potentially active TE families, two DNA elements (TF000728 and TF000742 in TEfam) are short and nonautonomous. Close inspection of the elements revealed that these two families were previously mis-categorized and, unlike other known TEs, insert specifically at dinucleotide “AT”. These two families were therefore designated as ATon-I and ATon-II. ATon-I has a total copy number of 294, among which three elements have more than 10 identical copies (146, 61 and 17). ATon-II has a total copy number of 317, among which three elements have more than 10 identical copies (84, 15 and 12). Genome wide searches revealed additional 24 ATon families in A. aegypti genome with nearly 6500 copies in total. Transposon display analysis of ATon-1 family using different A. aegypti strains suggests that the elements are similarly abundant in the tested mosquito strains.

Conclusion

ATons are novel mobile genetic elements bearing terminal inverted repeats and insert specifically at dinucleotide “AT”. Five ATon families contain elements existing at more than 10 identical copies, suggesting very recent or current transposition activity. A total of 24 new TE families with nearly 6000 copies were identified in this study.

A de novo transcriptome assembly of Lucilia sericata (Diptera: Calliphoridae) with predicted alternative splices, single nucleotide polymorphisms and transcript expression estimates

The blow fly Lucilia sericata (Diptera: Calliphoridae) (Meigen) is a nonmodel organism with no reference genome that is associated with numerous areas of research spanning the ecological, evolutionary, medical, veterinary and forensic sciences. To facilitate scientific discovery in this species, the transcriptome was assembled from more than six billion bases of Illumina and twenty-one million bases of 454 sequence derived from embryonic, larval, pupal, adult and larval salivary gland libraries. The assembly was carried out in a manner that enabled identification of putative single nucleotide polymorphisms (SNPs) and alternative splices, and that provided expression estimates for various life history stages and for salivary tissue. The assembled transcriptome was also used to identify transcribed transposable elements in L. sericata. The results of this study will enable blow fly biologists, dipterists and comparative genomicists to more rapidly develop and test molecular and genetic hypotheses, especially those regarding blow fly development and salivary gland biology.

Bioinformatics and genomic analysis of transposable elements in eukaryotic genomes

A major portion of most eukaryotic genomes are transposable elements (TEs). During evolution, TEs have introduced profound changes to genome size, structure, and function. As integral parts of genomes, the dynamic presence of TEs will continue to be a major force in reshaping genomes. Early computational analyses of TEs in genome sequences focused on filtering out "junk" sequences to facilitate gene annotation. When the high abundance and diversity of TEs in eukaryotic genomes were recognized, these early efforts transformed into the systematic genome-wide categorization and classification of TEs. The availability of genomic sequence data reversed the classical genetic approaches to discovering new TE families and superfamilies. Curated TE databases and their accurate annotation of genome sequences in turn facilitated the studies on TEs in a number of frontiers including: (1) TE-mediated changes of genome size and structure, (2) the influence of TEs on genome and gene functions, (3) TE regulation by host, (4) the evolution of TEs and their population dynamics, and (5) genomic scale studies of TE activity. Bioinformatics and genomic approaches have become an integral part of large-scale studies on TEs to extract information with pure in silico analyses or to assist wet lab experimental studies. The current revolution in genome sequencing technology facilitates further progress in the existing frontiers of research and emergence of new initiatives. The rapid generation of large-sequence datasets at record low costs on a routine basis is challenging the computing industry on storage capacity and manipulation speed and the bioinformatics community for improvement in algorithms and their implementations.

An automated homology-based approach for identifying transposable elements

Background

Transposable elements (TEs) are mobile sequences found in nearly all eukaryotic genomes. They have the ability to move and replicate within a genome, often influencing genome evolution and gene expression. The identification of TEs is an important part of every genome project. The number of sequenced genomes is rapidly rising, and the need to identify TEs within them is also growing. The ability to do this automatically and effectively in a manner similar to the methods used for genes is of increasing importance. There exist many difficulties in identifying TEs, including their tendency to degrade over time and that many do not adhere to a conserved structure. In this work, we describe a homology-based approach for the automatic identification of high-quality consensus TEs, aimed for use in the analysis of newly sequenced genomes.

Results

We describe a homology-based approach for the automatic identification of TEs in genomes. Our modular approach is dependent on a thorough and high-quality library of representative TEs. The implementation of the approach, named TESeeker, is BLAST-based, but also makes use of the CAP3 assembly program and the ClustalW2 multiple sequence alignment tool, as well as numerous BioPerl scripts. We apply our approach to newly sequenced genomes and successfully identify consensus TEs that are up to 99% identical to manually annotated TEs.

Conclusions

While TEs are known to be a major force in the evolution of genomes, the automatic identification of TEs in genomes is far from mature. In particular, there is a lack of automated homology-based approaches that produce high-quality TEs. Our approach is able to generate high-quality consensus TE sequences automatically, requiring the user to only provide a few basic parameters. This approach is intentionally modular, allowing researchers to use components separately or iteratively. Our approach is most effective for TEs with intact reading frames. The implementation, TESeeker, is available for download as a virtual appliance, while the library of representative TEs is available as a separate download.

From population structure to genetically-engineered vectors: New ways to control vector-borne diseases?

Epidemiological studies on vectors and the pathogens they can carry (such as Borrelia burgdorferi) are showing some correlations between infection rates and biodiversity highlighting the "dilution" effects on potential vectors. Meanwhile other studies comparing sympatric small rodent species demonstrated that rodent species transmitting more pathogens are parasitized by more ectoparasite species. Studies on population structure and size have also proven a difference on the intensity of the parasitic infection. Furthermore, preliminary results in genetic improvement in mosquitoes (genetic markers, sexing, and genetic sterilization) will also increase performance as it has already been shown in field applications in developing countries. Recent results have greatly improved the fitness of genetically-modified insects compared to wild type populations with new approaches such as the post-integration elimination of transposon sequences, stabilising any insertion in genetically-modified insects. Encouraging results using the Sterile Insect Technique highlighted some metabolism manipulation to avoid the viability of offspring from released parent insect in the wild. Recent studies on vector symbionts would also bring a new angle in vector control capabilities, while complete DNA sequencing of some arthropods could point out ways to block the deadly impact on animal and human populations. These new potential approaches will improve the levels of control or even in some cases would eradicate vector species and consequently the vector-borne diseases they can transmit. In this paper we review some of the population biology theories, biological control methods, and the genetic techniques that have been published in the last years that are recommended to control for vector-borne diseases.

Coadaptation and malaria control

Malaria emerges from a disequilibrium of the system 'human-plasmodium-mosquito' (HPM). If the equilibrium is maintained, malaria does not ensue and the result is asymptomatic plasmodium infection. The relationships among the components of the system involve coadaptive linkages that lead to equilibrium. A vast body of evidence supports this assumption, including the strategies involved in the relationships between plasmodium and human and mosquito immune systems, and the emergence of resistance of plasmodia to antimalarial drugs and of mosquitoes to insecticides. Coadaptive strategies for malaria control are based on the following principles: (1) the system HPM is composed of three highly complex and dynamic components, whose interplay involves coadaptive linkages that tend to maintain the equilibrium of the system; (2) human and mosquito immune systems play a central role in the coadaptive interplay with plasmodium, and hence, in the maintenance of the system's equilibrium; the under- or overfunction of human immune system may result in malaria and influence its severity; (3) coadaptation depends on genetic and epigenetic phenomena occurring at the interfaces of the components of the system, and may involve exchange of infectrons (genes or gene fragments) between the partners; (4) plasmodia and mosquitoes have been submitted to selective pressures, leading to adaptation, for an extremely long while and are, therefore, endowed with the capacity to circumvent both natural (immunity) and artificial (drugs, insecticides, vaccines) measures aiming at destroying them; (5) since malaria represents disequilibrium of the system HPM, its control should aim at maintaining or restoring this equilibrium; (6) the disequilibrium of integrated systems involves the disequilibrium of their components, therefore the maintenance or restoration of the system's equilibrium depend on the adoption of integrated and coordinated measures acting on all components, that means, panadaptive strategies. Coadaptive strategies for malaria control should consider that: (1) host immune response has to be induced, since without it, no coadaptation is attained; (2) the immune response has to be sustained and efficient enough to avoid plasmodium overgrowth; (3) the immune response should not destroy all parasites; (4) the immune response has to be well controlled in order to not harm the host. These conditions are mostly influenced by antimalarial drugs, and should also be taken into account for the development of coadaptive malaria vaccines.

nanos gene control DNA mediates developmentally regulated transposition in the yellow fever mosquito Aedes aegypti

Transposable elements (TEs) are proposed as a basis for developing drive systems to spread pathogen resistance genes through vector mosquito populations. The use of transcriptional and translational control DNA elements from genes expressed specifically in the insect germ line to mediate transposition offers possibilities for mitigating some of the concerns about transgene behavior in the target vector species and eliminating effects on nontarget organisms. Here, we describe the successful use of the promoter and untranslated regions from the nanos (nos) orthologous gene of the yellow fever mosquito, Aedes aegypti, to control sex- and tissue-specific expression of exogenously derived mariner MosI transposase-encoding DNA. Transgenic mosquitoes expressed transposase mRNA in abundance near or equal to the endogenous nos transcript and exclusively in the female germ cells. In addition, MosI mRNA was deposited in developing oocytes and localized and maintained at the posterior pole during early embryonic development. Importantly, four of five transgenic lines examined were capable of mobilizing a second MosI transgene into the mosquito genome, indicating that functional transposase was being produced. Thus, the nos control sequences show promise as part of a TE-based gene drive system.

Transposon-mediated resistance to Bacillus sphaericus in a field-evolved population of Culex pipiens (Diptera: Culicidae)

The binary toxin is the major active component of Bacillus sphaericus, a microbial larvicide used for controlling some vector mosquito-borne diseases. B. sphaericus resistance has been reported in many part of the world, leading to a growing concern for the usefulness of this environmental friendly insecticide. Here we characterize a novel mechanism of resistance to the binary toxin in a natural population of the West Nile virus vector, Culex pipiens. We show that the insertion of a transposable element-like DNA into the coding sequence of the midgut toxin receptor induces a new mRNA splicing event, unmasking cryptic donor and acceptor sites located in the host gene. The creation of the new intron causes the expression of an altered membrane protein, which is incapable of interacting with the toxin, thus providing the host mosquito with an advantageous phenotype. As a large portion of insect genomes is composed of transposable elements or transposable elements-related sequences, this new mechanism may be of general importance to appreciate their significance as potent agents for insect resistance to the microbial insecticides.

Insertion polymorphism of transposable elements and population structure of Anopheles gambiae M and S molecular forms in Cameroon

The insertion polymorphism of five transposable element (TE) families was studied by Southern blots in several populations of the M and S molecular forms of the mosquito Anopheles gambiae sensu stricto from southern Cameroon. We showed that the mean TE insertion site number and the within-population insertion site polymorphism globally differed between the M and S molecular forms. The comparison of the TE insertion profiles of the populations revealed a significant differentiation between these two molecular forms (0.163 < Phi(ST) < 0.371). We cloned several insertions of a non-LTR retrotransposon (Aara8) that were fixed in one form and absent in the other one. The only insertion that could be clearly located on a chromosome arm mapped to cytological division 6 of chromosome X, confirming the importance of this region in the ongoing speciation between the M and S molecular forms.

Distribution and Phylogeny of Penelope-Like Elements in Eukaryotes

Penelope-like elements (PLEs) are a relatively little studied class of eukaryotic retroelements, distinguished by the presence of the GIY-YIG endonuclease domain, the ability of some representatives to retain introns, and the similarity of PLE-encoded reverse transcriptases to telomerases. Although these retrotransposons are abundant in many animal genomes, the reverse transcriptase moiety can also be found in several protists, fungi, and plants, indicating its ancient origin. A comprehensive phylogenetic analysis of PLEs was conducted, based on extended sequence alignments and a considerably expanded data set. PLEs exhibit the pattern of evolution similar to that of non-LTR retrotransposons, which form deep-branching clades dating back to the Precambrian era. However, PLEs seem to have experienced a much higher degree of lineage losses than non-LTR retrotransposons. It is suggested that PLEs and non-LTR retrotransposons are included into a larger eTPRT (eukaryotic target-primed) group of retroelements, characterized by 5' truncation, variable target-site duplication, and the potential of the 3' end to participate in formation of non-autonomous derivatives.

Identification of Active Transposon dTok , a Member of the hAT Family, in Rice

Recent completion of the sequencing of the rice genome has revealed that it contains >40% repetitive sequences, most of which are related to inactive transposable elements. During the molecular analysis of the floral organ number 1/multiple pistil 2 (fon1/mp2) mutant, we identified an active transposable element dTok0 that was inserted at the kinase domain of FON1, a homolog of CLAVATA1. Insertion of the element into FON1 generated an 8 bp duplication of its target sites, which is one of the major characteristics of the hAT family of transposons. The dTok0 element was actively transposed out of the FON1 gene, leaving 5-8 bp footprints. Reinsertion into a new location was observed at a low frequency. Analysis of the genome sequence showed that the rice cultivar 'Nipponbare' contains 25 copies of dTok elements; similar numbers were present in all the Oryza species examined. Because dTok0 does not encode a transposase, enzyme activity should be provided in trans. We identified a putative autonomous transposon, Tok1 that contains an intact open reading frame of the Ac-like transposase.

Gene drive systems for insect disease vectors

The elegant mechanisms by which naturally occurring selfish genetic elements, such as transposable elements, meiotic drive genes, homing endonuclease genes and Wolbachia, spread at the expense of their hosts provide some of the most fascinating and remarkable subjects in evolutionary genetics. These elements also have enormous untapped potential to be used in the control of some of the world's most devastating diseases. Effective gene drive systems for spreading genes that can block the transmission of insect-borne pathogens are much needed. Here we explore the potential of natural gene drive systems and discuss the artificial constructs that could be envisaged for this purpose.

Reversible introduction of transgenes in natural populations of insects

The most serious challenge concerning genetically modified insects remains their invasion ability. Indeed, transgenic insects often show lower fitness than wild individuals, and the transgene does not seem able to spread through a natural population without a driving system. The use of remobilizable vectors, based on the invading properties of transposable elements, has been frequently suggested. Simulations show that this strategy can be efficient. Moreover, if the transgene is designed to use transposition machinery already present in the genome, the transgene invasion appears to be potentially reversible after a few hundred generations, leading to new experimental perspectives.

Mutant Mos1 mariner transposons are hyperactive in Aedes aegypti

The development of genetic strategies to control the spread of mosquito-borne diseases through the use of class II transposons has been hampered by suboptimal rates of transformation and the absence of post-integration mobility for all transposons evaluated to date. Two Mos1 mariner transposase mutants were produced by the site-directed mutagenesis of amino acids, E137 and E264, to K and R, respectively. The effects of these mutations on the transpositional activities of Mos1-derived transposon constructs were evaluated by interplasmid transposition assays in Escherichia coli and Aedes aegypti. The transpositional activities of two Mos1 transposons, one with imperfect wild type inverted terminal repeats (ITRs) and another that contained two perfectly matched 3' ITRs, were increased when the mutant transposases were supplied in trans in E. coli. The use of the perfect repeat transposon with wild type transposase did not result in an increase in transposition frequency in Ae. aegypti. However, an improvement in the integrity of the transposition process did occur, as evidenced by a lower rate of recombination events in which the transgene was transferred. An increase in the transpositional activity of the perfect repeat transposon was observed in the mosquito in the presence of either mutant transposase, and in the case of the E264R transposase, the observed increase in transposition frequency was also accompanied by a further improvement in the integrity of transposition. We discuss the possible contributions of these mutant residues to the transposition of the perfect repeat Mos1 transposon, the implications of these results with respect to the molecular evolution of Mos1, and the potential uses of the perfect repeat transposon and mutant transposases for the improvement of Mos1 mediated germ line transformation of Ae. aegypti.