The local environment and germline genetic variation predict cancer risk in the UK Biobank prospective cohort.

BACKGROUND: There is a growing body of evidence on the effect of the local environment exposure on cancer susceptibility. Nonetheless, several of the associations remain controversial. Moreover, our understanding of the possible interaction between the local environment and the genetic variability is still very limited. OBJECTIVE: The aim of this study was to clarify the role of the local environment and its possible interplay with genetics on common cancers development. METHODS: Using the UK Biobank (UKBB) prospective cohort, we selected 12 local environment exposures: nitrogen oxides, nitrogen dioxides, particulate matter (10 and 2.5 µm), noise pollution, urban traffic, living distance from the coast, percentage of greenspace, natural environment, water, and domestic garden within 1000 m from the residential coordinates of each participant. All these exposures were tested for association with 17 different types of cancer for a total of 53,270 cases and 302,645 controls. Additionally, a polygenic score (PGS) was computed for each cancer, to test possible gene-environment interactions. Finally, mediation analyses were carried out. RESULTS: Thirty-six statistically significant associations considering multiple testing (p < 2.19 × 10-4) were observed. Among the novel associations we observed that individuals living farther from the coast had a higher risk of developing prostate cancer (OR = 1.13, CI95% = 1.06-1.20, P = 1.98 × 10-4). This association was partially mediated by physical activity (indirect effect (IE) = -8.48 × 10-7) and the time spent outdoor (IE = 9.07 × 10-6). All PGSs showed statistically significant associations. Finally, genome-environment interaction analysis showed that local environment and genetic variability affect cancer risk independently. DISCUSSION: Living close to the coast and air pollution were associated with a decreased risk of prostate cancer and skin melanoma, respectively. These findings from the UKBB support the role of the local environment on cancer development, which is independent from genetics and may be mediated by several lifestyle factors.

Comparison of immediate germline sequencing and multi-step screening for Lynch syndrome detection in high-risk endometrial and colorectal cancer patients.

OBJECTIVE: Lynch syndrome (LS) is a hereditary cancer predisposition syndrome with a significantly increased risk of colorectal and endometrial cancers. Current standard practice involves universal screening for LS in patients with newly diagnosed colorectal or endometrial cancer using a multi-step screening protocol (MSP). However, MSP may not always accurately identify LS cases. To address this limitation, we compared the diagnostic performance of immediate germline sequencing (IGS) with MSP in a high-risk group. METHODS: A total of 31 Taiwanese women with synchronous or metachronous endometrial and colorectal malignancies underwent MSP which included immunohistochemical staining of DNA mismatch repair (MMR) proteins, MLH1 promoter hypermethylation analysis, and germline sequencing to identify pathogenic variants. All patients who were excluded during MSP received germline sequencing for MMR genes to simulate IGS for the detection of LS. RESULTS: Our findings indicate that IGS surpassed MSP in terms of diagnostic yield (29.0% vs. 19.4%, respectively) and sensitivity (90% vs. 60%, respectively). Specifically, IGS successfully identified nine LS cases, which is 50% more than the number detected through MSP. Additionally, germline methylation analysis revealed one more LS case with constitutional MLH1 promoter hypermethylation, bringing the total LS cases to ten (32.3%). Intriguingly, we observed no significant differences in clinical characteristics or overall survival between patients with and without LS in our cohort. CONCLUSION: Our study suggests that IGS may potentially offer a more effective approach compared to MSP in identifying LS among high-risk patients. This advantage is evident when patients have been pre-selected utilizing specific clinical criteria.

Germline and sporadic mTOR pathway mutations in low-grade oncocytic tumor of the kidney.

Low-grade oncocytic tumor (LOT) of the kidney is a recently described entity with poorly understood pathogenesis. Using next-generation sequencing (NGS) and complementary approaches, we provide insight into its biology. We describe 22 LOT corresponding to 7 patients presenting with a median age of 75 years (range 63-86 years) and male to female ratio 2:5. All 22 tumors demonstrated prototypical microscopic features. Tumors were well-circumscribed and solid. They were composed of sheets of tumor cells in compact nests. Tumor cells had eosinophilic cytoplasm, round to oval nuclei (without nuclear membrane irregularities), focal subtle perinuclear halos, and occasional binucleation. Sharply delineated edematous stromal islands were often observed. Tumor cells were positive for PAX8, negative for CD117, and exhibited diffuse and strong cytokeratin-7 expression. Six patients presented with pT1 tumors. At a median follow-up of 29 months, four patients were alive without recurrence (three patients had died from unrelated causes). All tumors were originally classified as chromophobe renal cell carcinoma, eosinophilic variant (chRCC-eo). While none of the patients presented with known syndromic features, one patient with multiple bilateral LOTs was subsequently found to have a likely pathogenic germline TSC1 mutation. Somatic, likely activating, mutations in MTOR and RHEB were identified in all other evaluable LOTs. As assessed by phospho-S6 and phospho-4E-BP1, mTOR complex 1 (mTORC1) was activated across all cases but to different extent. MTOR mutant LOT exhibited lower levels of mTORC1 activation, possibly related to mTORC1 dimerization and the preservation of a wild-type MTOR copy (retained chromosome 1). Supporting its distinction from related entities, gene expression analyses showed that LOT clustered separately from classic chRCC, chRCC-eo, and RO. In summary, converging mTORC1 pathway mutations, mTORC1 complex activation, and a distinctive gene expression signature along with characteristic phenotypic features support LOT designation as a distinct entity with both syndromic and non-syndromic cases associated with an indolent course.

Misleading Germ Cell Phenotype in Pulmonary NUT Carcinoma Harboring the ZNF532-NUTM1 Fusion.

NUT carcinoma (aka NUT midline carcinoma) is a rare, still significantly underrecognized aggressive malignancy. Although historically considered a midline malignancy of children and young adults, NUT carcinoma can originate in almost any body site and in any age group. Beside the classic BRD4-NUTM1 fusion, less common fusion partners include BRD3, NSD3, ZNF532, and ZNF592. Other fusions, including CIC, MGA, MXD4, MXD1, and BCORL1 are associated with sarcomas or cancers of unknown histogenesis. Involvement of the Z4 zinc finger protein (ZNF) family members ZNF532 and ZNF592 is exceedingly rare with only 3 recently reported cases. We herein describe a ZNF532-NUTM1-rearranged NUT carcinoma presenting as a 7.5 cm mass in the left lower lung lobe of a 65-year-old woman. Histology revealed undifferentiated monotonous small round cells with focal epithelioid and rhabdoid elements within a variably myxoid stroma. Immunohistochemistry revealed paucity of keratins and variable p63 combined with extensive CD30 and PLAP expression, leading to initial diagnoses of combined small cell carcinoma, CD30-positive unclassified hematolymphoid malignancy and malignant germ cell neoplasm. Negativity for other more specific germ cell markers justified seeking a fourth opinion, which revealed diffuse expression of the NUT antibody. The diagnosis was then confirmed by fluorescence in situ hybridization. Targeted RNA sequencing revealed the ZNF532-NUTM1 fusion. Screening of 7 NUT carcinomas (5 with BRD4-NUTM1 and 2 with NSD3-NUTM1 fusions) for germ cell markers revealed focal SALL4 reactivity in 3 cases (combined with variable AFP expression in 2), but none expressed CD30 or PLAP. An aberrant germ cell immunophenotype should be considered in NUT carcinoma to avoid misinterpretation as genuine germ cell malignancy as both diseases predominantly affect the young population, frequently involve the mediastinum and can be associated with elevated serum AFP.

Comparative evaluation of the antioxidant, antimicrobial and nutritive properties of gluten-free flours.

Gluten-free flours are interesting alternative to wheat flours. They could be by-products of oilseed processing, characterized by high content of bioactive compounds. Therefore the aim of the study was to determine the antioxidant, antimicrobial properties, amino acid and fatty acid profile of flours obtained as by-products from the oil industry. The highest total polyphenol content and antioxidant activity was found to have evening primrose flour. The widest spectrum of microbial growth inhibition was indicated for corn germ extract which showed no antimicrobial activity only against Bacillus subtilis. The highest protein content was found in pumpkin, peanut and almond flours (more than 50 g/100 g). The major abundant amino acids in all the analysed oilseed cake flours were aspartic acid, glutamic acid and arginine. The analysed gluten-free flours were found to be a good source of polyunsaturated fatty acids (PUFAs), which comprised mainly linoleic acid and α-linolenic acid, whereas the best source of PUFAs was evening primrose flour. The results suggest that the cold-pressed seed flours possess valuable chemical composition and may be considered for improvement of the nutritional properties of food products.

Postulated Process of Axoneme Organization in the Male Gametogenesis of Malaria Parasite Plasmodium berghei.

The ultrastructural features of axoneme organization within the cytoplasm and exflagellation were investigated in detail in microgametes of a malaria parasite, Plasmodium berghei, by electron and fluorescence microscopy. The kinetosomes (basal bodies) of the microgamete were characterized by an electron dense mass in which singlet microtubules (MTs) were embedded. Around the kinetosomes, several singlet and doublet MTs were recognized in transverse sections. Incomplete doublets with growing B-tubule were also observed. As precursors of the axoneme, arrays of over three doublets showed a tendency to encircle the central pair MTs. Some of the doublet MTs were already equipped with inner and outer dynein arms. In the microgamete, which lacks an intraflagellar transport (IFT) system, self-assembly of microtubular and associated components appeared to proceed stepwise from singlet MTs through arrays of one to nine doublet MTs, surrounding the central pair, to form the complete axoneme in a quite short time. At exflagellation, some extra doublets were occasionally included between the axoneme and the flagellar membrane. At high magnification, the outer dynein arm of the Plasmodium microgamete had a pistol-like shape representing a three-headed dynein molecule like that of other Alveolata.

Evaluating DNA damage response through immunofluorescence staining of primordial germ cells in Caenorhabditis elegans L1 larva.

C. elegans L1 larvae have two well-defined primordial germ cells embedded in a niche comprising two somatic gonad precursor cells. Thus, C. elegans provides an ideal model for studying intercellular signaling in response to DNA damage. However, existing staining protocols are focused on worms in later developmental stages and are not optimized for the L1 larvae. Here, we present a revised protocol for assessing the DNA damage response utilizing immunofluorescence staining specifically in C. elegans L1 larva. For complete details on the use and execution of this protocol, please refer to Ou et al. (2019).

Distinctive regulatory architectures of germline-active and somatic genes in C. elegans.

RNA profiling has provided increasingly detailed knowledge of gene expression patterns, yet the different regulatory architectures that drive them are not well understood. To address this, we profiled and compared transcriptional and regulatory element activities across five tissues of Caenorhabditis elegans, covering ∼90% of cells. We find that the majority of promoters and enhancers have tissue-specific accessibility, and we discover regulatory grammars associated with ubiquitous, germline, and somatic tissue-specific gene expression patterns. In addition, we find that germline-active and soma-specific promoters have distinct features. Germline-active promoters have well-positioned +1 and -1 nucleosomes associated with a periodic 10-bp WW signal (W = A/T). Somatic tissue-specific promoters lack positioned nucleosomes and this signal, have wide nucleosome-depleted regions, and are more enriched for core promoter elements, which largely differ between tissues. We observe the 10-bp periodic WW signal at ubiquitous promoters in other animals, suggesting it is an ancient conserved signal. Our results show fundamental differences in regulatory architectures of germline and somatic tissue-specific genes, uncover regulatory rules for generating diverse gene expression patterns, and provide a tissue-specific resource for future studies.

Sex and sex-related differences in gamete development progression impinge on biomarker responsiveness in sentinel mussels.

In marine pollution monitoring, the biomarkers recorded in sentinel organisms are influenced by natural confounding factors that may jeopardise their interpretation. Among these confounding factors, little is known about the influence of sex along the annual reproductive cycle. The present investigation aims at contributing to understand how sex and sex-related differences in gamete development progression impinge on biomarker baseline values and on biomarker responsiveness to pollution in sentinel mussels. Mussels (Mytilus galloprovincialis) were collected from a relatively clean locality and from a chronically polluted site in the Basque Coast (Bay of Biscay) in January, April, August and November. Sex and gametogenesis stages were determined for each mussel. Tissue concentration of metals and PAHs was analysed. A battery of biomarkers was investigated: cytochrome c oxidase, pyruvate kinase and phosphoenolpyruvate carboxykinase enzyme activities; levels of protein carbonyls, malondialdehyde and 4-hydroxy-2-nonenal; lysosomal enlargement and membrane stability; intracellular neutral lipid accumulation; cell type composition and thinning of the digestive gland epithelium; and survival-in-air. Sex- and reproductive stage-related differences were found in bioaccumulation and in the values and responsiveness of most of the biomarkers. However, the patterns of sex-related differences were not consistent across all biomarkers. The differences in the biomarker responses between females and males also depended on the season, reflecting the progression of the gametogenesis cycle. Thus, selecting mussels of one specific sex does not seem to be a crucial requisite to carry out biomarker-based monitoring; yet, it is highly recommended to identify sex condition and gamete developmental stage of each mussel to test for the potentially confounding effects of sex, reproductive status and sex-related variability along the reproductive cycle.

Micronuclei in germ cells of hybrid frogs from Pelophylax esculentus complex contain gradually eliminated chromosomes.

In most organisms, cells typically maintain genome integrity, as radical genome reorganization leads to dramatic consequences. However, certain organisms, ranging from unicellular ciliates to vertebrates, are able to selectively eliminate specific parts of their genome during certain stages of development. Moreover, partial or complete elimination of one of the parental genomes occurs in interspecies hybrids reproducing asexually. Although several examples of this phenomenon are known, the molecular and cellular processes involved in selective elimination of genetic material remain largely undescribed for the majority of such organisms. Here, we elucidate the process of selective genome elimination in water frog hybrids from the Pelophylax esculentus complex reproducing through hybridogenesis. Specifically, in the gonads of diploid and triploid hybrids, but not those of the parental species, we revealed micronuclei in the cytoplasm of germ cells. In each micronucleus, only one centromere was detected with antibodies against kinetochore proteins, suggesting that each micronucleus comprises a single chromosome. Using 3D-FISH with species-specific centromeric probe, we determined the role of micronuclei in selective genome elimination. We found that in triploid LLR hybrids, micronuclei preferentially contain P. ridibundus chromosomes, while in diploid hybrids, micronuclei preferentially contain P. lessonae chromosomes. The number of centromere signals in the nuclei suggested that germ cells were aneuploid until they eliminate the whole chromosomal set of one of the parental species. Furthermore, in diploid hybrids, misaligned P. lessonae chromosomes were observed during the metaphase stage of germ cells division, suggesting their possible elimination due to the inability to attach to the spindle and segregate properly. Additionally, we described gonocytes with an increased number of P. ridibundus centromeres, indicating duplication of the genetic material. We conclude that selective genome elimination from germ cells of diploid and triploid hybrids occurs via the gradual elimination of individual chromosomes of one of the parental genomes, which are enclosed within micronuclei.

Genome Size and Sex Chromosome Variability of Bed Bugs Feeding on Animal Hosts Compared to Cimex lectularius Parasitizing Human (Heteroptera: Cimicidae).

Genome size and chromosome number of five Cimicidae species were compared with the similar data recently received from Cimex lectularius parasitizing human. The average nuclear DNA content (males) was 2C = 1.47 pg in C. hemipterus, 2C = 1.61 pg in C. hirundinis, 2C = 1.80 pg in C. lectularius from bats, 2C = 1.68 pg in C. pipistrelli, and 2C = 1.22 pg in Paracimex cf. chaeturus. In the genomes of all cimicid species analyzed, the average GC content ranged from 32.74% in C. pipistrelli to 35.87% in P. cf. chaeturus. Chromosome variability with two male cytotypes, 2n = 28 + X1 X2 Y and 28 + X1 X2 X3 Y, was confirmed in C. pipistrelli. In addition, intraspecific variability in chromosome number was revealed in C. lectularius from bats with 2n = 26 + X1 X2 Y and 26 + X1 X2 X3 Y. We suggest that the origin of intraspecific variability in chromosome number of C. lectularius from bats and C. pipistrelli is not only the result of simple fragmentation, but additive rearrangements like duplications are probably also involved. © 2019 International Society for Advancement of Cytometry.

Broad Heterochromatic Domains Open in Gonocyte Development Prior to De Novo DNA Methylation.

Facultative heterochromatin forms and reorganizes in response to external stimuli. However, how the initial establishment of such a chromatin state is regulated in cell-cycle-arrested cells remains unexplored. Mouse gonocytes are arrested male germ cells, at which stage the genome-wide DNA methylome forms. Here, we discovered transiently accessible heterochromatin domains of several megabases in size in gonocytes and named them differentially accessible domains (DADs). Open DADs formed in gene desert and gene cluster regions, primarily at transposons, with the reprogramming of histone marks, suggesting DADs as facultative heterochromatin. De novo DNA methylation took place with two waves in gonocytes: the first region specific and the second genome-wide. DADs were resistant to the first wave and their opening preceded the second wave. In addition, the higher-order chromosome architecture was reorganized with less defined chromosome compartments in gonocytes. These findings suggest that multiple layers of chromatin reprogramming facilitate de novo DNA methylation.

High-resolution analysis of germ cells from men with sex chromosomal aneuploidies reveals normal transcriptome but impaired imprinting.

BACKGROUND: The most common sex chromosomal aneuploidy in males is Klinefelter syndrome, which is characterized by at least one supernumerary X chromosome. While these men have long been considered infertile, focal spermatogenesis can be observed in some patients, and sperm can be surgically retrieved and used for artificial reproductive techniques. Although these gametes can be used for fertility treatments, little is known about the molecular biology of the germline in Klinefelter men. Specifically, it is unclear if germ cells in Klinefelter syndrome correctly establish the androgenetic DNA methylation profile and transcriptome. This is due to the low number of germ cells in the Klinefelter testes available for analysis. RESULTS: Here, we overcame these difficulties and successfully investigated the epigenetic and transcriptional profiles of germ cells in Klinefelter patients employing deep bisulfite sequencing and single-cell RNA sequencing. On the transcriptional level, the germ cells from Klinefelter men clustered together with the differentiation stages of normal spermatogenesis. Klinefelter germ cells showed a normal DNA methylation profile of selected germ cell-specific markers compared with spermatogonia and sperm from men with normal spermatogenesis. However, germ cells from Klinefelter patients showed variations in the DNA methylation of imprinted regions. CONCLUSIONS: These data indicate that Klinefelter germ cells have a normal transcriptome but might present aberrant imprinting, showing impairment in germ cell development that goes beyond mere germ cell loss.

Recognition of Listeria Infection by Germline Elements of the Vγ1.1 Vδ6.3 TCR.

γδNKT cells are an abundant γδT cell population with restricted Vγ1.1 Vδ6.3 gene usage and phenotypic and functional similarity to conventional αß-invariant NKT cells. The γδNKT population responds to Listeria infections, but specific ligands are not known. In this work, we studied the CDR3 requirements of the γδNKT TCR, Vγ1.1Vδ6.3 for recognizing naive macrophages, and macrophages infected with Listeria We expressed four different variants of the Vγ1.1Vδ6.3 TCR in TCR-deficient hybridomas, one with germline-encoded sequences and three with nongermline-encoded sequences. All of the hybridomas were activated when cultured in the presence of macrophages, and the activation was increased when the macrophages were infected with Listeria This indicates that these TCRs can recognize a self-ligand present in macrophages and suggests that the ligand is modified or upregulated when the cells are infected with Listeria One of the three nongermline-encoded Vγ1.1 variants induced a lower activation level compared with the other variants tested in this study, suggesting that recognition of the Listeria-induced ligand involves the CDR3γ region of the TCR.

'Significant breakthrough' in evolutionary avian genetics.

Georgina Mills discusses recent research into songbirds, which looked at how they differ from other avian species.

Bacterial expression, purification and biophysical characterization of wheat germ agglutinin and its four hevein-like domains.

Wheat germ agglutinin (WGA), a chitin binding lectin, has attracted increasing interest because of its unique characteristics such as conformational stability, binding specificity and transcytosis capacity. To pave the way for the study of the molecular basis of WGA's structural stability and binding capacity, as well as to facilitate its use in biomedical and biotechnological developments, we produced recombinant WGA and its 4 isolated hevein-like domains in a bacterial system. All the proteins were expressed as fusion constructs linked to a thioredoxin domain, which was enzymatically or chemically released. The structural and ligand-binding properties of recombinant WGA were similar to the wild lectin. The 4 isolated domains folded and were ligand-binding competent, indicating that each domain constitutes an independent folding unity. The biophysical characterization of the recombinant domains sheds new light on the intricate folding and binding behavior of this emblematic lectin.

Germline genetic testing for inherited prostate cancer in practice: Implications for genetic testing, precision therapy, and cascade testing.

BACKGROUND: Genetic testing capability and guidelines are rapidly expanding to assess inherited prostate cancer (PCA). Clinical genetic data from multigene testing can provide insights into the germline pathogenic variant (PV) spectrum and correlates in men with PCA unselected for metastatic disease to optimize identification of men for genetic evaluation and management. METHODS: A retrospective cross-sectional analysis was conducted of de-identified clinical genetic testing data from a large commercial genetic testing laboratory in the US. ICD-10 claims codes were used to identify men with PCA, along with family history data. Gleason score was abstracted from test request forms. Overall PV rate among men with PCA was estimated, along with PVs in DNA repair genes. Family history and Gleason score association to germline DNA repair PVs was assessed using Fisher's exact test with correction for false-discovery. RESULTS: As of August 2017, genetic results were available on 1328 men with PCA. Overall PV rate was 15.6%, with 10.9% of PV in DNA repair genes. PVs were most commonly identified in BRCA2 (4.5%), CHEK2 (2.2%), ATM (1.8%), and BRCA1 (1.1%). Breast cancer family history was significantly associated with germline DNA repair PVs (OR 1.89, [95%CI 1.33, 2.68], P = 0.003). Among men with Gleason score>= 6 (n = 706), Gleason> = 8 was significantly associated with DNA repair PVs (OR 1.85 [95%CI 1.22, 2.80], P = 0.004). CONCLUSIONS: A substantial proportion of men with PCA unselected for metastatic disease carry germline DNA repair PVs. Breast cancer family history and high Gleason score are important predictors to identify men with PCA who may carry germline DNA repair PVs. Our findings support current NCCN guidelines and have implications for genetic assessment, therapeutic management, and cascade testing for men with PCA and their families.

Dnd is required for primordial germ cell specification in Oryzias celebensis.

Dead end (dnd) is a germ plasm component that plays an essential role for primordial germ cell (PGC) development in vertebrates. Previously, we have found that dnd is the first fish PGC specifier in medaka. Here, we present an additional evidence that dnd is the determinant for PGC specification in Oryzias celebensis. In adult tissues, the O. celebensis dnd (Ocdnd) RNA shows germ cells specific expression in gonads. In the testis, Ocdnd RNA is strongly detected in spermatogonia and meiotic cells and gradually decreases during the spermatogenesis. In the ovary, Ocdnd RNA is present throughout oogenesis. In the embryos, Ocdnd RNA is maternally provided and asymmetrically localized to prominent particles of presumptive PGCs before gastrulation stage and restricted to PGCs subsequently. In addition, Ocdnd 3' UTR can induce specific and stabilized GFP reporter expression in PGCs. Furthermore, knockdown of Ocdnd by morpholino (MO) injection abolishes the PGCs formation and this can be rescued by co-injection of medaka dnd (Oldnd) mRNA. More importantly, overexpression of Oldnd mRNA surprisingly boosts PGCs number. These results provide insights into function of dnd as a conserved specifier of PGCs in the genus Oryzias.

Key role of piRNAs in telomeric chromatin maintenance and telomere nuclear positioning in Drosophila germline.

BACKGROUND: Telomeric small RNAs related to PIWI-interacting RNAs (piRNAs) have been described in various eukaryotes; however, their role in germline-specific telomere function remains poorly understood. Using a Drosophila model, we performed an in-depth study of the biogenesis of telomeric piRNAs and their function in telomere homeostasis in the germline. RESULTS: To fully characterize telomeric piRNA clusters, we integrated the data obtained from analysis of endogenous telomeric repeats, as well as transgenes inserted into different telomeric and subtelomeric regions. The small RNA-seq data from strains carrying telomeric transgenes demonstrated that all transgenes belong to a class of dual-strand piRNA clusters; however, their capacity to produce piRNAs varies significantly. Rhino, a paralog of heterochromatic protein 1 (HP1) expressed exclusively in the germline, is associated with all telomeric transgenes, but its enrichment correlates with the abundance of transgenic piRNAs. It is likely that this heterogeneity is determined by the sequence peculiarities of telomeric retrotransposons. In contrast to the heterochromatic non-telomeric germline piRNA clusters, piRNA loss leads to a dramatic decrease in HP1, Rhino, and trimethylated histone H3 lysine 9 in telomeric regions. Therefore, the presence of piRNAs is required for the maintenance of telomere chromatin in the germline. Moreover, piRNA loss causes telomere translocation from the nuclear periphery toward the nuclear interior but does not affect telomere end capping. Analysis of the telomere-associated sequences (TASs) chromatin revealed strong tissue specificity. In the germline, TASs are enriched with HP1 and Rhino, in contrast to somatic tissues, where they are repressed by Polycomb group proteins. CONCLUSIONS: piRNAs play an essential role in the assembly of telomeric chromatin, as well as in nuclear telomere positioning in the germline. Telomeric arrays and TASs belong to a unique type of Rhino-dependent piRNA clusters with transcripts that serve simultaneously as piRNA precursors and as their only targets. Telomeric chromatin is highly sensitive to piRNA loss, implying the existence of a novel developmental checkpoint that depends on telomere integrity in the germline.