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Protein homeostasis involves the ubiquitously expressed heterodimeric protein NAC (ribosome associated nascent polypeptide complex), consisting of α- and β-subunits. We previously found inDrosophila melanogasterthe presence of germline-specific paralogous genes for NAC subunits (gNACs): unique for the α-subunit and several highly homologous amplified genes for the β-subunit, indistinguishable by the antibodies used, while they were detected as different phosphorylated isoforms in 2D electrophoresis with immunostaining. The distinct increase in gNAC expression in growing spermatocytes compared with their predecessors, gonioblasts, is accompanied by a clear presence of gNAC in the cytoplasm of dividing meiotic cells and spermatids. In oogenesis, gNAC expression is significantly lower than in the testis, but gNAC accumulation is found at the posterior pole of the mature oocyte, known as the germplasm region responsible for the germ cell formation in the offspring. gNAC-associated ribosomes from mature oocytes are enriched in mRNA sets encoding known germplasm and centrosome proteins. gNAC is also detected in a pericentriolar component of centrosomes: in syncytial dividing nuclei in the early embryos, in primordial germ cells and spermatocytes, including meiotic divisions stage. CRISPR/Cas9-mediated deficiency of the gNAC-alpha subunit causes female infertility. We propose the role of the gNAC phosphoregulatory paralog system as a component of the germline proteostasis network, coordinated with the centrosome functions. Here, we also extended our results by identifying cross-links between ubiquitous and germline-specific NAC-β paralogs, finding an additional case of functional cross-talk between heterodimeric ubNAC and gNAC α-subunit paralogs, which may maintain the robustness of proteostasis and fly fecundity.

The nascent polypeptide-associated complex (NAC) consisting of α- and β-subunits is an essential conserved ribosome-associated protein in eukaryotes. NAC is considered as a ubiquitously expressed co-translational regulator of nascent protein folding and sorting providing homeostasis of cellular proteins. Here we discovered the germline-specific NACαβ paralogs (gNACs), whose β-subunits, non-distinguishable by ordinary immunodetection, being encoded by five highly homologous gene copies while α-subunit is encoded by the single αNAC gene. Immunostaining detects the gNAC expression in the primordial embryonic and adult gonads. The germline specific α and β subunits differ from the ubiquitously expressed paralogs by the acquisition of extended intrinsically disordered regions (IDRs) at the N- and C-ends of coding regions, respectively, which were predicted to be phosphorylated. The presence of distinct phosphorylated isoforms of gNAC-β subunits is confirmed by comparison of their profiles by 2D-isoeletrophocusing resolution before and after phosphatase treatment of testis ribosomes. We propose IDR-dependent molecular crowding and specific coordination of the NAC and other proteostasis regulatory factors in the ribosomes of germinal cells. A possibility of the functional crosstalk’s between the germinal and ubiquitous α- and β- subunits is revealed by assessing their depletion effects on the fly viability and gonad development.

Eukaryotic genomes harbor hundreds of rRNA genes, many of which are transcriptionally silent. However, little is known about selective regulation of individual rDNA units. In Drosophila melanogaster, some rDNA repeats contain insertions of the R2 retrotransposon, which is capable to be transcribed only as part of pre-rRNA molecules. rDNA units with R2 insertions are usually inactivated, although R2 expression may be beneficial in cells with decreased rDNA copy number. Here we found that R2-inserted rDNA units are enriched with HP1a and H3K9me3 repressive mark, whereas disruption of the heterochromatin components slightly affects their silencing in ovarian germ cells. Surprisingly, we observed a dramatic upregulation of R2-inserted rRNA genes in ovaries lacking Udd (Under-developed) or other subunits (TAF1b and TAF1c-like) of the SL1-like complex, which is homologues to mammalian Selective factor 1 (SL1) involved in rDNA transcription initiation. Derepression of rRNA genes with R2 insertions was accompanied by a reduction of H3K9me3 and HP1a enrichment. We suggest that the impairment of the SL1-like complex affects a mechanism of selective activation of intact rDNA units which competes with heterochromatin formation. We also propose that R2 derepression may serve as an adaptive response to compromised rRNA synthesis.

In the Drosophila ovary, somatic escort cells (ECs) form a niche that promotes differentiation of germline stem cell (GSC) progeny. The piRNA (Piwi-interacting RNA) pathway, which represses transposable elements (TEs), is required in ECs to prevent the accumulation of undifferentiated germ cells (germline tumor phenotype). The soma-specific piRNA cluster flamenco (flam) produces a substantial part of somatic piRNAs. Here, we characterized the biological effects of somatic TE activation on germ cell differentiation in flam mutants. We revealed that the choice between normal and tumorous phenotypes of flam mutant ovaries depends on the number of persisting ECs, which is determined at the larval stage. Accordingly, we found much more frequent DNA breaks in somatic cells of flam larval ovaries than in adult ECs. The absence of Chk2 or ATM checkpoint kinases dramatically enhanced oogenesis defects of flam mutants, in contrast to the germline TE-induced defects that are known to be mostly suppressed by сhk2 mutation. These results demonstrate a crucial role of checkpoint kinases in protecting niche cells against deleterious TE activation and suggest substantial differences between DNA damage responses in ovarian somatic and germ cells.

In Drosophila ovarian somatic cells, PIWI-interacting small RNAs (piRNAs) against transposable elements are mainly produced from the ∼180-kb flamenco ( flam) locus. flam transcripts are gathered into foci, located close to the nuclear envelope, and processed into piRNAs in the cytoplasmic Yb bodies. The mechanism of Yb body formation remains unknown. Using RNA fluorescence in situ hybridization, we found that in the follicle cells of ovaries the 5′-ends of flam transcripts are usually located in close proximity to the nuclear envelope and outside of Yb bodies, whereas their extended downstream regions mostly overlap with Yb bodies. In flamKGmutant ovaries, flam transcripts containing the first and, partially, second exons but lacking downstream regions are gathered into foci at the nuclear envelope, but Yb bodies are not assembled. Strikingly, piRNAs from the protein-coding gene transcripts accumulate at higher levels in flamKGovaries indicating that piRNA biogenesis may occur without Yb bodies. We propose that normally in follicle cells, flam downstream transcript regions function not only as a substrate for generation of piRNAs but also as a scaffold for Yb body assembly, which competitively decreases piRNA production from the protein-coding gene transcripts. By contrast, in ovarian somatic cap and escort cells Yb body assembly does not require flam transcription.

Telomeres are nucleoprotein complexes that protect the ends of eukaryotic linear chromosomes from degradation and fusions. Telomere dysfunction leads to cell growth arrest, oncogenesis, and premature aging. Telomeric RNAs have been found in all studied species; however, their functions and biogenesis are not clearly understood. We studied the mechanisms of development disorders observed upon overexpression of telomeric repeats in Drosophila. In somatic cells, overexpression of telomeric retrotransposon HeT-A is cytotoxic and leads to the accumulation of HeT-A Gag near centrosomes. We found that RNA and RNA-binding protein Gag encoded by the telomeric retrotransposon HeT-A interact with Polo and Cdk1 mitotic kinases, which are conserved regulators of centrosome biogenesis and cell cycle. The depletion of proteins Spindle E, Ccr4 or Ars2 resulting in HeT-A overexpression in the germline was accompanied by mislocalization of Polo as well as its abnormal stabilization during oogenesis and severe deregulation of centrosome biogenesis leading to maternal-effect embryonic lethality. These data suggest a mechanistic link between telomeric HeT-A ribonucleoproteins and cell cycle regulators that ensures the cell response to telomere dysfunction.

This article pursues the aim of scrutinizing stand-up comedy in order to analyze and determine the impact of globalization and internationalization set on entertainment industry as a whole and the way comedians perform their acts in particular. It is the first time the acts of comedians from three different cultures are analyzed in the light of phono-pragmatic research. Perceptive analysis is implemented to find out the main suprasegmental characteristics used by the comedians. This work presents an interdisciplinary research based on social and pragmatic linguistics, sociophonetics, phono-pragmatic analysis where comedians` social, cultural and geographical background, the context as well as social and linguistic peculiarities of this genre are taken into consideration. Alongside with these methods a proper linguistic method is used: a method of socio-phonetic and pragma-phonetic investigation. The authors arrive at the conclusion that the speakers tend to stick to their style of performance and their native manner of pronunciation. Meanwhile, their stand-up is preserved in the international manner of the genre. The research data supports the claim that the comedians adopt the stylistic features of American stand-up and sound American if they perform in a style of a stand-up. Thus, the results of this work allow to speak about unification concerning the style, genre and some speech patterns regardless of the actor’s geographical, social and cultural origin.

Eukaryotic genomes contain hundreds of nearly identical rRNA genes, many of which are transcriptionally silent. However, the mechanisms of selective regulation of individual rDNA units remain poorly understood. InDrosophila melanogaster, rDNA repeats containing insertions of R1/R2 retrotransposons within the 28S rRNA sequence undergo inactivation. Here we found that rRNA genes with insertions are specifically enriched with H3K9me3 and HP1a repressive marks, but disruption of heterochromatin components only slightly affects their silencing. Intriguingly, the loss of Udd (Under-developed) protein interacting with Pol I transcription initiation complex, causes an upregulation of R2-inserted rDNA copies in germ cells by two orders of magnitude that is accompanied by the reduction of heterochromatin marks. Thus, for the first time we revealed a factor required for distinguishing between active and silent rDNA units to such a large extent. To clarify a relationship between the rDNA transcriptional status and heterochromatin establishment, we showed that inhibition of transcription by actinomycin D increases the level of H3K9me3 mark erasing the epigenetic differences between inserted and uninserted rRNA genes. Altogether, we suggest that Udd coupled with Pol I transcription initiation machinery defines activation or silencing of individual rDNA units, whereas their transcription level consequently dictates their chromatin state.

How the nuclear lamina (NL) impacts on global chromatin architecture is poorly understood. Here, we show that NL disruption in Drosophila S2 cells leads to chromatin compaction and repositioning from the nuclear envelope. This increases the chromatin density in a fraction of topologically-associating domains (TADs) enriched in active chromatin and enhances interactions between active and inactive chromatin. Importantly, upon NL disruption the NL-associated TADs become more acetylated at histone H3 and less compact, while background transcription is derepressed. Two-colour FISH confirms that a TAD becomes less compact following its release from the NL. Finally, polymer simulations show that chromatin binding to the NL can per se compact attached TADs. Collectively, our findings demonstrate a dual function of the NL in shaping the 3D genome. Attachment of TADs to the NL makes them more condensed but decreases the overall chromatin density in the nucleus by stretching interphase chromosomes., The role of the nuclear lamina (NL) in chromatin architecture is still poorly understood. Here, the authors provide evidence that disruption of the NL in Drosophila cells leads to overall chromatin compaction and repositioning from the nuclear envelope, whereas lamina-associated regions become less compacted and transcription within them is increased.

Piwi in a complex with Piwi-interacting RNAs (piRNAs) triggers transcriptional silencing of transposable elements (TEs) in Drosophila ovaries, thus ensuring genome stability. To do this, Piwi must scan the nascent transcripts of genes and TEs for complementarity to piRNAs. The mechanism of this scanning is currently unknown. Here we report the DamID-seq mapping of multiple Piwi-interacting chromosomal domains in somatic cells of Drosophila ovaries. These domains significantly overlap with genomic regions tethered to Nuclear Pore Complexes (NPCs). Accordingly, Piwi was coimmunoprecipitated with the component of NPCs Elys and with the Xmas-2 subunit of RNA transcription and export complex, known to interact with NPCs. However, only a small Piwi fraction has transient access to DNA at nuclear pores. Importantly, although 36% of the protein-coding genes overlap with Piwi-interacting domains and RNA-immunoprecipitation results demonstrate promiscuous Piwi binding to numerous genic and TE nuclear transcripts, according to available data Piwi does not silence these genes, likely due to the absence of perfect base-pairing between piRNAs and their transcripts.

In Drosophila ovarian somatic cells, PIWI-interacting small RNAs (piRNAs) against transposable elements are mainly produced from the ∼180-kb flamenco (flam) locus. flam transcripts are gathered into foci, located close to the nuclear envelope, and processed into piRNAs in the cytoplasmic Yb bodies. The mechanism of Yb body formation remains unknown. Using RNA fluorescence in situ hybridization, we found that in the follicle cells of ovaries the 5′-ends of flam transcripts are usually located in close proximity to the nuclear envelope and outside of Yb bodies, whereas their extended downstream regions mostly overlap with Yb bodies. In flamKG mutant ovaries, flam transcripts containing the first and, partially, second exons but lacking downstream regions are gathered into foci at the nuclear envelope, but Yb bodies are not assembled. Strikingly, piRNAs from the protein-coding gene transcripts accumulate at higher levels in flamKG ovaries indicating that piRNA biogenesis may occur without Yb bodies. We propose that normally in follicle cells, flam downstream transcript regions function not only as a substrate for generation of piRNAs but also as a scaffold for Yb body assembly, which competitively decreases piRNA production from the protein-coding gene transcripts. By contrast, in ovarian somatic cap and escort cells Yb body assembly does not require flam transcription.

The Piwi protein and its orthologs are considered as the key components of the piRNA machinery implicated in transcriptional silencing of transposons. Неre, we show that nuclear localization of the Piwi protein is required not only for transposon repression, but also for proper differentiation of germline stem cells (GSCs). piwi Nt mutation that causes loss of nuclear Piwi and its retention in the cytoplasm leads to the accumulation of undifferentiated GSC-like cells. The analysis of piwi Nt mutation in combination with a bam gene mutation blocking GSC differentiation shows that the loss of nuclear Piwi decreases GSC proliferation rate. This is accompanied by the accumulation of DNA double-strand breaks in GSCs that may be caused by transposition events. Here, for the first time a set of transposons repressed by Piwi in GSCs and surrounding niche cells has been identified. The present study together with our previous data show that nuclear and cytoplasmic Piwi can regulate different stages of the functioning of germinal cells: cytoplasmic Piwi is sufficient to maintain GSCs, while nuclear Piwi localization is necessary for their proper proliferation and differentiation.

Background In most mammalian cell lines, chromatin located at the nuclear periphery is represented by condensed heterochromatin, as evidenced by microscopy observations and DamID mapping of lamina-associated domains (LADs) enriched in dimethylated Lys9 of histone H3 (H3K9me2). However, in Kc167 cell culture, the only Drosophilla cell type where LADs have previously been mapped, they are neither H3K9me2-enriched nor overlapped with the domains of heterochromatin protein 1a (HP1a). Results Here, using cell type-specific DamID we mapped genome-wide LADs, HP1a and Polycomb (Pc) domains from the central brain, Repo-positive glia, Elav-positive neurons and the fat body of Drosophila third instar larvae. Strikingly, contrary to Kc167 cells of embryonic origin, in neurons and, to a lesser extent, in glia and the fat body, HP1a domains appear to overlap strongly with LADs in both the chromosome arms and pericentromeric regions. Accordingly, centromeres reside closer to the nuclear lamina in neurons than in Kc167 cells. As expected, active gene promoters are mostly not present in LADs, HP1a and Pc domains. These domains are occupied by silent or weakly expressed genes with genes residing in the HP1a-bound LADs expressed at the lowest level. Conclusions In various differentiated Drosophila cell types, we discovered the existence of peripheral heterochromatin, similar to that observed in mammals. Our findings support the model that peripheral heterochromatin matures enhancing the repression of unwanted genes as cells terminally differentiate. Electronic supplementary material The online version of this article (10.1186/s13072-018-0235-8) contains supplementary material, which is available to authorized users.

The evolutionarily conserved nuclear Piwi protein of Drosophila melanogaster is the defining member of the Argonaute small RNA-binding protein family. Guided by piRNAs, Piwi functions in transposon silencing in somatic and germ cells of gonads. We found that in ovarian somatic and germ cells, as well as in the established ovarian somatic cell line, Piwi accumulates predominantly in the nucleolus, the main nuclear compartment which participates not only in rRNA synthesis, but also in various cell stress responses. We have shown the colocalization of Piwi with the nucleolar marker proteins fibrillarin and Nopp140. The piwi Nt mutation which prevents the transport of Piwi to the nucleus and disrupts transposon silencing led to 6-8 fold upregulation of rRNA gene expression, as assessed by the level of transcripts of transposon insertions in 28S rRNA genes. RNase treatment of live cultured ovarian somatic cells depleted Piwi from the nucleolus. The same effect was observed upon inhibition of the activity of RNA polymerase I, which transcribes rRNA genes, but not RNA polymerase II. In contrast, upon heat shock, Piwi concentrated in the nucleolus and was depleted from the nucleoplasm. These results implicate Piwi in RNA polymerase I activity modulation and stress response in the nucleolus. Possible noncanonical Piwi functions are discussed, which are not related to the role of Piwi in transposon silencing.

The development of the reproductive organs and the gametogenesis in animals are complex and multistage processes that require the precise and efficient regulation. In this review, we summarized the recent findings about the essential functions of microRNAs (miRNAs) in the regulation of gene expression during the differentiation of germ cells in spermatogenesis and oogenesis. Most likely, main and common functions of the conserved and highly expressed miRNAs in the male and female reproductive organs of mammals are the control of differentiation and proliferation of cells. Also we discussed a possible involvement of germline-expressed miRNAs in the formation of reproductive barriers and speciation.

Piwi-interacting RNAs (piRNAs) and Piwi proteins have the evolutionarily conserved function of silencing of repetitive genetic elements in germ lines. The founder of the Piwi subfamily, Drosophila nuclear Piwi protein, was also shown to be required for the maintenance of germ-line stem cells (GSCs). Hence, null mutant piwi females exhibit two types of abnormalities, overexpression of transposons and severely underdeveloped ovaries. It remained unknown whether the failure of GSC maintenance is related to transposon derepression or if GSC self-renewal and piRNA silencing are two distinct functions of the Piwi protein. We have revealed a mutation, piwi Nt , removing the nuclear localization signal of the Piwi protein. piwi Nt females retain the ability of GSC self-renewal and a near-normal number of egg chambers in the ovarioles but display a drastic transposable element derepression and nuclear accumulation of their transcripts in the germ line. piwi Nt mutants are sterile most likely because of the disturbance of piRNA-mediated transposon silencing. Analysis of chromatin modifications in the piwi Nt ovaries indicated that Piwi causes chromatin silencing only of certain types of transposons, whereas others are repressed in the nuclei without their chromatin modification. Thus, Piwi nuclear localization that is required for its silencing function is not essential for the maintenance of GSCs. We suggest that the Piwi function in GSC self-renewal is independent of transposon repression and is normally realized in the cytoplasm of GSC niche cells.

Complexes of Piwi family proteins with short piRNAs (Piwi-interacting RNAs) are responsible for silencing transposable elements in animal reproductive organs. In Drosophila melanogaster, three proteins (Piwi, Aub, and Ago3) are members of the Piwi family. Piwi is the nuclear protein of somatic and germinal ovarian cells, whereas Aub and Ago3 are cytoplasmic proteins involved in piRNA amplification in perinuclear granules that constitute special organelles of germinal cells called nuage. Mutations in genes of the piRNA system are known to cause derepression of several transposable elements. In this study, we compared quantitatively changes in expression of a larger number of elements in the case of mutations in the piwi gene, genes aub, mael, and spn-E, which encode proteins of nuage granules, and armi gene coding an RNA helicase, the lack of which does not interfere with cytoplasmic piRNA amplification but disturbs nuclear localization of Piwi protein. We found that the genes piwi, armi, aub, spn-E, and mael interact to induce silencing of some retrotransposons (HMS-Beagle, Gate and HeT-A); the same genes, except piwi, are involved in repression of I and G elements. We propose that Armi is involved in control of not only nuclear Piwi localization. Our data suggest the relation of nuage proteins Aub, Spn-E, and Mael to Piwi-mediated silencing of retrotransposons Gate and HMS-Beagle in the nucleus. In general, our results corroborate the idea of genome stabilization by means of various silencing strategies specific to different transposable elements. At the same time, our data suggest the existence of yet unknown mechanisms of interplay between nuclear and cytoplasmic components of the piRNA machinery in germinal cells.

Recent advances enabled by the Hi-C technique have unraveled many principles of chromosomal folding that were subsequently linked to disease and gene regulation. In particular, Hi-C revealed that chromosomes of animals are organized into topologically associating domains (TADs), evolutionary conserved compact chromatin domains that influence gene expression. Mechanisms that underlie partitioning of the genome into TADs remain poorly understood. To explore principles of TAD folding inDrosophila melanogaster, we performed Hi-C and poly(A)+RNA-seq in four cell lines of various origins (S2, Kc167, DmBG3-c2, and OSC). Contrary to previous studies, we find that regions between TADs (i.e., the inter-TADs and TAD boundaries) inDrosophilaare only weakly enriched with the insulator protein dCTCF, while another insulator protein Su(Hw) is preferentially present within TADs. However,Drosophilainter-TADs harbor active chromatin and constitutively transcribed (housekeeping) genes. Accordingly, we find that binding of insulator proteins dCTCF and Su(Hw) predicts TAD boundaries much worse than active chromatin marks do. Interestingly, inter-TADs correspond to decompacted inter-bands of polytene chromosomes, whereas TADs mostly correspond to densely packed bands. Collectively, our results suggest that TADs are condensed chromatin domains depleted in active chromatin marks, separated by regions of active chromatin. We propose the mechanism of TAD self-assembly based on the ability of nucleosomes from inactive chromatin to aggregate, and lack of this ability in acetylated nucleosomal arrays. Finally, we test this hypothesis by polymer simulations and find that TAD partitioning may be explained by different modes of inter-nucleosomal interactions for active and inactive chromatin.

MicroRNAs are a wide class of ~22 nt non-coding RNAs of metazoans capable of inhibiting target mRNAs translation by binding to partially complementary sites in their 3′UTRs. Due to their regulatory potential, miRNAs are implicated in functioning of a broad range of biological pathways and processes. Here we investigate the functions of the miR-959-964 cluster expressed predominantly in testes ofDrosophila melanogaster. The deletion of miR-959-964 resulted in male sterility due to the disturbance of the spermatid individualization process. Analysis of the transcriptome by microarray followed by luciferase reporter assay revealeddidum,for,fdland CG10512 as the targets of miR-959-964. Moreover, the deletion of miR-959-964 is accompanied by a decreased the expression of genes responsible for microtubule-based movement and spermatid differentiation. Thus, we suggest that miR-959-964 can control the process of spermatid individualization by direct and indirect modulating the expression of different components of the individualization process. In addition, we have shown that in comparison to other miRNAs, the rate of evolution of the testis-specific miR-959-964 cluster is unusually high, indicating its possible involvement in speciation via reproductive isolation.

A mucin-type glycoprotein (GP) from cultured embryonic cells of Drosophila melanogaster was isolated and used to raise monoclonal antibodies (MAbs). Epitope(s) recognized by MAbs were sensitive to the treatment by O-glycanase, which specifically cleaves off O-linked mucin-type Gal(beta 1,3)GalNAc disaccharide, representing the major part of the carbohydrate moiety of Drosophila GP. Using high-affinity MAbs against carbohydrate epitopes of the Drosophila mucin GP we demonstrated its accumulation in culture medium, as well as in cultured cells, which proved to be regulated by 20-hydroxyecdysone. Mucin GPs carrying Gal(beta 1,3)GalNAc disaccharide recognized by the MAbs were immunochemically localized in several Drosophila tissues of ectodermal, mesodermal and germ line origin, including epidermal and follicle cells capable of their secretion.

Theoretical models suggest that gene silencing at the nuclear periphery may involve "closing" of chromatin by transcriptional repressors, such as histone deacetylases (HDACs). Here we provide experimental evidence confirming these predictions. Histone acetylation, chromatin compactness, and gene repression in lamina-interacting multigenic chromatin domains were analyzed in Drosophila S2 cells in which B-type lamin, diverse HDACs, and lamina-associated proteins were downregulated by dsRNA. Lamin depletion resulted in decreased compactness of the repressed multigenic domain associated with its detachment from the lamina and enhanced histone acetylation. Our data reveal the major role for HDAC1 in mediating deacetylation, chromatin compaction, and gene silencing in the multigenic domain, and an auxiliary role for HDAC3 that is required for retention of the domain at the lamina. These findings demonstrate the manifold and central involvement of class I HDACs in regulation of lamina-associated genes, illuminating a mechanism by which these enzymes can orchestrate normal and pathological development.

A secreted glycoprotein (GP) with apparent molecular mass of 90 kDa produced by cultured embryonic cells of Drosophila melanogaster was isolated and partially characterized. GP is enriched by Ser + Thr and Pro residues that constitute up to 30% of the total number of amino acids. An abundant carbohydrate moiety (40% of molecular mass) is mainly represented by vertebrate mucin-type O-linked disaccharide units Gal(β1–3)-GalNAc, occupying about a half of the total number of Ser + Thr residues and rendering the GP molecule high resistance to protease action. A few of N-glycans are also present in GP. These characteristics allow to consider the Drosophila GP (termed ‘mucin-D’) as a first representative of invertebrate mucin-type glycoproteins.