Chromatoid Body Research Articles

Maybe repressed mRNAs are not stored in the chromatoid body in mammalian spermatids

The chromatoid body is a dynamic organelle that is thought to coordinate the cytoplasmic regulation of mRNA translation and degradation in mammalian spermatids. The chromatoid body is also postulated to function in repression of mRNA translation by sequestering dormant mRNAs where they are inaccessible to the translational apparatus. This review finds no convincing evidence that dormant mRNAs are localized exclusively in the chromatoid body. This discrepancy can be explained by two hypotheses. First, experimental artifacts, possibly related to peculiarities of the structure and function of the chromatoid body, preclude obtaining an accurate indication of mRNA localization. Second, mRNA is not stored in the chromatoid body, because, like perinuclear P granules in Caenorhabditis elegans, the chromatoid body functions as a center for mRNP remodeling and export to other cytoplasmic sites.

Tudor domain containing 7 ( Tdrd7 ) is essential for dynamic ribonucleoprotein (RNP) remodeling of chromatoid bodies during spermatogenesis

In the male germline in mammals, chromatoid bodies, a specialized assembly of cytoplasmic ribonucleoprotein (RNP), are structurally evident during meiosis and haploidgenesis, but their developmental origin and regulation remain elusive. The tudor domain containing proteins constitute a conserved class of chromatoid body components. We show that tudor domain containing 7 (Tdrd7), the deficiency of which causes male sterility and age-related cataract (as well as glaucoma), is essential for haploid spermatid development and defines, in concert with Tdrd6, key biogenesis processes of chromatoid bodies. Single and double knockouts of Tdrd7 and Tdrd6 demonstrated that these spermiogenic tudor genes orchestrate developmental programs for ordered remodeling of chromatoid bodies, including the initial establishment, subsequent RNP fusion with ubiquitous processing bodies/GW bodies and later structural maintenance. Tdrd7 suppresses LINE1 retrotransposons independently of piwi-interacting RNA (piRNA) biogenesis wherein Tdrd1 and Tdrd9 operate, indicating that distinct Tdrd pathways act against retrotransposons in the male germline. Tdrd6, in contrast, does not affect retrotransposons but functions at a later stage of spermiogenesis when chromatoid bodies exhibit aggresome-like properties. Our results delineate that chromatoid bodies assemble as an integrated compartment incorporating both germline and ubiquitous features as spermatogenesis proceeds and that the conserved tudor family genes act as master regulators of this unique RNP remodeling, which is genetically linked to the male germline integrity in mammals.

Chromatoid body and small RNAs in male germ cells

The chromatoid body (CB) is a germ granule in the cytoplasm of postmeiotic haploid round spermatids that is loaded with RNA and RNA-binding proteins. Following the discovery of small non-coding RNA-mediated gene regulation and the identification of PIWI-interacting RNAs (piRNAs) that have crucial roles in germ line development, the function of the CB has slowly begun to be revealed. Male germ cells utilise small RNAs to control the complex and specialised process of sperm production. Several microRNAs have been identified during spermatogenesis. In addition, a high number of piRNAs are present both in embryonic and postnatal male germ cells, with their expression being impressively induced in late meiotic cells and haploid round spermatids. At postmeiotic stage of germ cell differentiation, the CB accumulates piRNAs and proteins of piRNA machinery, as well as several other proteins involved in distinct RNA regulation pathways. All existing evidence suggests a role for the CB in mRNA regulation and small RNA-mediated gene control, but the mechanisms remain uncharacterised. In this review, we summarise the current knowledge of the CB and its association with small RNA pathways.

Étude ultrastructurale de l’ovogenèse chez la planaire Schmidtea mediterranea (Plathelminthe, Paludicole)

The ovary of the freshwater planarian Schmidtea mediterranea has been studied for the first time using both light and electron microscopy methods. The ultrastructure of the ovary revealed two types of cells: accessory cells and germinal cells at various stages of differentiation, distributed along a maturation axis. Initially, oogonia underwent cytoplasm growth due to the development of organelles, such as endoplasmic reticulum, Golgi complex, and mitochondria, which are all involved in the production of cytoplasmic inclusions or yolk globules. It is shown that the chromatoid body and fibrogranular aggregates may participate in the synthesis of vitelline inclusions. When completely mature, the oocytes have become larger, due to the accumulation of nutritive inclusions, which are round in shape and have a paracrystalline structure. These inclusions are interpreted as being yolk globules and may represent a kind of nutritive material for the developing embryo. These ultrastructural features of the ovary agree with the available phylogenetic tree, based on morphological and karyological characters that considers Schmidtea group as a genus and not a subgenus. The presence of sperm between the oocytes suggests that fertilization may occur within the ovary, representing an uncommon condition within the Triclads, in which fertilization usually takes places outside of the ovaries.

Pinpointing the expression of piRNAs and function of the PIWI protein subfamily during spermatogenesis in the mouse

PIWI proteins and piRNAs have been linked to transposon silencing in the primordial mouse testis, but their function in the adult testis remains elusive. Here we report the cytological characterization of piRNAs in the adult mouse testis and the phenotypic analysis of Miwi−/−; Mili−/− mice. We show that piRNAs are specifically present in germ cells, especially abundant in spermatocytes and early round spermatids, regardless of the type of the genomic sequences to which they correspond. piRNAs and PIWI proteins are present in both the cytoplasm and nucleus. In the cytoplasm, they are enriched in the chromatoid body; whereas in the nucleus they are enriched in the dense body, a male-specific organelle associated with synapsis and the formation of the XY body during meiosis. Moreover, by generating Miwi−/−; Mili−/− mice, which lack all PIWI proteins in the adult, we show that PIWI proteins and presumably piRNAs in the adult are required only for spermatogenesis. Spermatocytes without PIWI proteins are arrested at the pachytene stage, when the sex chromosomes undergo transcriptional silencing to form the XY body. These results pinpoint a function of the PIWI protein subfamily to meiosis during spermatogenesis.

TDRD5 is required for retrotransposon silencing, chromatoid body assembly, and spermiogenesis in mice

The Tudor domain-containing proteins (TDRDs) are an evolutionarily conserved family of proteins involved in germ cell development. We show here that in mice, TDRD5 is a novel component of the intermitochondrial cements (IMCs) and the chromatoid bodies (CBs), which are cytoplasmic ribonucleoprotein granules involved in RNA processing for spermatogenesis. Tdrd5-deficient males are sterile because of spermiogenic arrest at the round spermatid stage, with occasional failure in meiotic prophase. Without TDRD5, IMCs and CBs are disorganized, with mislocalization of their key components, including TDRD1/6/7/9 and MIWI/MILI/MIWI2. In addition, Tdrd5-deficient germ cells fail to repress LINE-1 retrotransposons with DNA-demethylated promoters. Cyclic adenosine monophosphate response element modulator (CREM) and TRF2, key transcription factors for spermiogenesis, are expressed in Tdrd5-deficient round spermatids, but their targets, including Prm1/Prm2/Tnp1, are severely down-regulated, which indicates the importance of IMC/CB-mediated regulation for postmeiotic gene expression. Strikingly, Tdrd5-deficient round spermatids injected into oocytes contribute to fertile offspring, demonstrating that acquisition of a functional haploid genome may be uncoupled from TDRD5 function.

Ultrastructure of spermatogenesis in the white-lined broad-nosed bat, Platyrrhinus lineatus (Chiroptera: Phyllostomidae)

Spermatogenesis, the remarkable process of morphological and biochemical transformation and cell division of diploid stem cells into haploid elongated spermatozoa, is one of the most complex cell differentiations found in animals. This differentiation process has attracted extensive studies, not only because the process involves many radical changes in the cell shape and biochemistry, but also because the phases and steps of differentiation have provided a better basis for analyzing the seminiferous epithelium cycle. Thus, this study aimed to characterize ultrastructurally the spermatogenesis process in the bat Platyrrhinus lineatus in order to provide a basis for determining the stages of spermatogenesis and to facilitate comparisons of the process between bat species and other vertebrates. Based on ultrastructural characteristics three main types of spermatogonia could be accurately identified: A d, A p and B; the differentiation of spermatids was clearly divided into 12 steps (steps 1–3: Golgi phase, steps 4–5: cap phase, steps 6–9: acrosomal phase and steps 10–12: maturation phase). The ultrastructure of spermatozoa, Leydig cells and Sertoli cells was characterized; and some processes including nucleolar disorganization and the formation of synaptonemal complexes, acrosome and chromatoid body were discussed. Based on our results we may conclude that the spermatogenic process of P. lineatus follows the pattern of mammals with some specificity, as the process of formation of the acrosome and the presence of the perfuratorium. By other side, the simpler ultrastructure of its spermatozoon shows a pattern more closely related to the sperm cells of humans and other primates.

Differential Conservation and Divergence of Fertility Genes boule and dazl in the Rainbow Trout

BackgroundThe genes boule and dazl are members of the DAZ (Deleted in Azoospermia) family encoding RNA binding proteins essential for germ cell development. Although dazl exhibits bisexual expression in mitotic and meiotic germ cells in diverse animals, boule shows unisexual meiotic expression in invertebrates and mammals but a bisexual mitotic and meiotic expression in medaka. How boule and dazl have evolved different expression patterns in diverse organisms has remained unknown.Methodology and Principal FindingsHere we chose the fish rainbow trout (Oncorhynchus mykiss) as a second lower vertebrate model to investigate the expression of boule and dazl. By molecular cloning and sequence comparison, we identified cDNAs encoding the trout Boule and Dazl proteins, which have a conserved RNA-recognition motif and a maximal similarity to their homologs. By RT-PCR analysis, adult RNA expression of trout boule and dazl is restricted to the gonads of both sexes. By chromogenic and two-color fluorescence in situ hybridization, we revealed bisexual and germline-specific expression of boule and dazl. We found that dazl displays conserved expression throughout gametogenesis and concentrates in the Balbinani's body of early oocytes and the chromatoid body of sperm. Surprisingly, boule exhibits mitotic and meiotic expression in the male but meiosis-specific expression in the female.ConclusionsOur data underscores differential conservation and divergence of DAZ family genes during vertebrate evolution. We propose a model in which the diversity of boule expression in sex and stage specificity might have resulted from selective loss or gain of its expression in one sex and mitotic germ cells.

Thesis Abstract Chagas disease and triatomine biology (Heteroptera, Triatominae), with emphasis on aspects of spermatogenesis

A century after the discovery of Chagas disease, it is still one of the most important parasitic diseases affecting humans. The subfamily Triatominae is important in medical health, because these insects are vectors of Trypanosoma cruzi, the etiologic agent of Chagas disease. These insects are also of important cytological relevance because they have particular cell characteristics, such as persistence of nucleolar material in spermatogenesis. The germ cells of the animal kingdom have chromatoid bodies (CBs) in their cytoplasm that can originate from nucleolar material that is fragmented in the early stages of spermatogenesis and plays an important role in cellular communication between the spermatids during spermiogenesis. Currently, there are few studies on the function and formation of the CB in nucleologenesis, especially with emphasis on the ultrastructure of the cells involved in spermatogenesis of insects. Considering the importance of knowledge about the triatomine fauna, we conducted a study of the biogeography and reports of these insects and a survey of patients with Chagas disease in the northwestern region of Sao Paulo State. Data collected from 1995 to 2009 indicated 700 individuals with Chagas disease, demonstrating a range of 0 to 40 years, which shows that the disease may be active in this region. Moreover, of the 1150 patients treated for cardiomyopathy, 44% were chagasic. Regarding the triatomines noted and captured in the period from 2004 to 2009, the species were Triatoma sordida and Rhodnius neglectus, with T. sordida being the most abundant. In addition, some triatomines were infected by T. cruzi in various developmental stages. We also analyzed the nucleolar cycle and fibrillarin nucleolar protein expression in CB of spermatogenic cells of T. infestans and T. sordida, using histological, ultrastructural and immunocytochemical techniques. The results revealed fibrillarin nucleolar protein expression in the nucleus and in some cytoplasmic spots of germ cells during spermatogenesis in triatomines. These data suggest that fibrillarin could be a constituent of CB, which was most likely derived from nucleolar fragmentation. This is the first time that fibrillarin protein expression has been shown in CB during spermatogenesis progression in triatomines. Knowledge about the biology of triatomines was deepened in this study and, in particular, the structural and ultrastructural aspects of spermatogenesis in triatomines. This study showed that the disease may be active in the northwestern region of Sao Paulo and expanded our knowledge of the biology of triatomines, the main vectors of Chagas disease.

Non-coding RNAs enter mitosis: functions, conservation and implications

Nuage (or commonly known as chromatoid body in mammals) is a conserved germline-specific organelle that has been linked to the Piwi-interacting RNA (piRNA) pathway. piRNAs are a class of gonadal-specific RNAs that are ~23-29 nucleotides in length and protect genome stability by repressing the expression of deleterious retrotransposons. More recent studies in Drosophila have implicated the piRNA pathway in other functions including canalization of embryonic development, regulation of maternal gene expression and telomere protection. We have recently shown that Vasa (known as Mouse Vasa Homolog in mouse), a nuage component, plays a mitotic role in promoting chromosome condensation and segregation by facilitating robust chromosomal localization of condensin I in the Drosophila germline. Vasa functions together with Aubergine (a PIWI family protein) and Spindle-E/mouse TDRD-9, two other nuage components that are involved in the piRNA pathway, therefore providing a link between the piRNA pathway and mitotic chromosome condensation. Here, we propose and discuss possible models for the role of Vasa and the piRNA pathway during mitosis. We also highlight relevant studies implicating mitotic roles for RNAs and/or nuage in other model systems and their implications for cancer development.

Regulation of Translational Suppression in Post-Meiotic Germ Cells: Crosstalk Between MicroRNAs and Actin-Associated Proteins.

During male germ cell development, the vast majority of mRNAs is translationally repressed at the post-meiotic stage. While individual components implicated in the transcriptional and posttranscriptional control of specific germ cell gene expression have been identified, the mechanism that coordinates widespread translational suppression during germ cell differentiation remains unclear. In this study, we established that the cross-talk between miRNAs and actin-associated protein sets the tone for the mRNA-specific as well as general uncoupling of transcription and translation during post-meiotic germ cell maturation. Our study reveals that loss of the miRNA-processing enzyme Dicer function in haploid spermatids causes altered translational activation of several post-meiotic germ cell-specific transcripts, resulting in abnormal chromatin compaction and impaired fertility. We identified a specific miRNA-targeted actin-associated protein 2/3 complex (Arpc) subunit that plays a crucial role in this process as it sequesters germ cell-specific transcripts through their 3' UTR into translationally inert RNP complexes, and making them inaccessible to translational machinery. Interestingly, this actin-associated protein mediates translational suppression by interacting with GW182, a component of processing and chromatoid bodies, discrete cytoplasmic foci in the somatic and germ cells, respectively, believed to play an instrumental role in the storage and degradation of translationally suppressed mRNA. Collectively, our findings suggest that miRNAs are important checkpoint regulators that control timely expression of genes critical for post-meiotic germ cell differentiation and add a new dimension to the increasing role of actin and actin-associated proteins in post-transcriptional gene regulation. In light of recent studies showing an association between altered expression of actin-binding proteins and poor semen quality in human males, we propose that miRNA(s) targeting this Arpc subunit may serve as novel biomarkers for defective sperm and impaired male fertility. This research is funded by the NIH (HD053774-03). (platform)

Nucleolar cycle and chromatoid body formation: Is there a relationship between these two processes during spermatogenesis of Dendropsophus minutus (Amphibia, Anura)?

The goals of this study were to monitor the nucleolar material distribution during Dendropsophus minutus spermatogenesis using cytological and cytochemical techniques and ultrastructural analysis, as well as to compare the nucleolar material distribution to the formation of the chromatoid body (CB) in the germ epithelium of this amphibian species. Nucleolar fragmentation occurred during the pachytene of prophase I and nucleolus reorganization occurred in the early spermatid nucleus. The area of the spermatogonia nucleolus was significantly larger than that of the earlier spermatid nucleolus. Ultrastructural analysis showed an accumulation of nuages in the spermatogonia cytoplasm, which form the CB before nucleolar fragmentation. The CB was observed in association with mitochondrial clusters in the cytoplasm of primary spermatocytes, as well as in those of earlier spermatids. In conclusion, the nucleolus seems to be related to CB formation during spermatogenesis of D. minutus, because, at the moment of nucleolus fragmentation in the primary spermatocytes, the CB area reaches a considerable size and is able to execute its important functions during spermatogenesis. The reorganized nucleolus of the earlier spermatids has a smaller area due to several factors, among them the probable migration of nucleolar fragments from the nucleus to the cytoplasm, and plays a part in the CB chemical composition.

FIGLA, a Basic Helix-Loop-Helix Transcription Factor, Balances Sexually Dimorphic Gene Expression in Postnatal Oocytes

Maintenance of sex-specific germ cells requires balanced activation and repression of genetic hierarchies to ensure gender-appropriate development in mammals. Figla (factor in the germ line, alpha) encodes a germ cell-specific basic helix-loop-helix transcription factor first identified as an activator of oocyte genes. In comparing the ovarian proteome of normal and Figla null newborn mice, 18 testis-specific or -enhanced proteins were identified that were more abundant in Figla null ovaries than in normal ovaries. Transgenic mice, ectopically expressing Figla in male germ cells, downregulated a subset of these genes and demonstrated age-related sterility associated with impaired meiosis and germ cell apoptosis. Testis-associated genes, including Tdrd1, Tdrd6, and Tdrd7, were suppressed in the transgenic males with a corresponding disruption of the sperm chromatoid body and mislocalization of MVH and MILI proteins, previously implicated in posttranscriptional processing of RNA. These data demonstrate that physiological expression of Figla plays a critical dual role in activation of oocyte-associated genes and repression of sperm-associated genes during normal postnatal oogenesis.

Characterization of Mongolian Gerbil Chromatoid Bodies and Their Correlation with Nucleolar Cycle During Spermatogenesis

The aims of the present study were to monitor the nucleolar cycle in Mongolian gerbil spermiogenesis, to verify the relationship between the nucleolar component and chromatoid body (CB) formation and to investigate the function of this cytoplasmic supramolecular structure in spermatogenic cells. Histological sections of adult seminiferous tubules were analysed cytochemically by light microscopy and ultrastructurally by transmission electron microscopy. The results reveal that in early spermatids, the CB was visualized in association with Golgi vesicles indicating that this structure may participate in the acrosome formation process as had been reported in other rodents. In late spermatids, the CB was observed near the axoneme region suggesting that this structure may support spermatozoon tail formation as happens in other species. Chromatoid body was joined with lipid droplets in this same cell type. This observation should be investigated to verify whether CB may be related to steroidal hormone metabolism. In conclusion, our data showed that there is disintegration of primary spermatocyte nucleoli at the beginning of prophase I and a fraction of this nucleolar material migrates to the cytoplasm, where a specific structure is formed, known as the 'chromatoid body', which apparently participates in some parts of the gerbil spermiogenesis process.

Nucleolar Cycle and Its Correlation with Chromatoid Bodies in the Tilapia rendalli (Teleostei, Cichlidae) Spermatogenesis

The aim of this study was: (1) to monitor the nucleolar material distribution using cytological and cytochemical techniques and ultrastructural analysis; and (2) to compare the nucleolar material distribution with the formation of the chromatoid body (CB) in the germ epithelium of Tilapia rendalli. Nucleolar fragmentation occurred during the leptotene of prophase I and nucleolus reorganization occurred in the early spermatid nucleus. The area of the early spermatid nucleolus was significantly smaller than that of the spermatogonia nucleolus. Ultrastructural analysis showed an accumulation of nuages, which form the CB, before nucleolar fragmentation in the spermatogonia cytoplasm. The CB was observed in association with mitochondrial clusters in the cytoplasm of primary spermatocytes, as well as in those of initial and later spermatids. In conclusion, the nucleolus seems to be related to CB formation during spermatogenesis of T. rendalli, because at the moment of nucleolus fragmentation in the primary spermatocytes, the CB reaches its largest area and it is able to complete important functions during spermatogenesis. The reorganized nucleolus of the initial spermatids has a lower area due several factors, one of which is the probable migration of nucleolar fragments from the nucleus to the cytoplasm, therefore playing a role in CB formation.

Localization of mouse vasa homolog protein in chromatoid body and related nuage structures of mammalian spermatogenic cells during spermatogenesis

The localization of vasa homolog protein in the spermatogenic cells of mice, rats, and guinea pigs was studied by immunofluorescence and electron microscopies with the antibody against mouse vasa homolog (MVH) protein. By immunofluorescence microscopy, four types of granular staining patterns were identified: (1) fine particles observed in diplotene and meiotic cells, (2) small granules associated with a mitochondrial marker and appearing in pachytene spermatocytes after stage V, (3) strands lacking the mitochondrial marker in late spermatocytes, and (4) large irregularly shaped granules in round spermatids. Immunoelectron microscopy defined the ultrastructural profiles of these MVH protein-positive granules: the first type consisted of small dense particles, the second had intermitochondrial cement (IMC), the third type, consisting of strands, had loose aggregates of either material dissociated from IMC or 70-90-nm particles, and the fourth had typical chromatoid bodies (CBs). The results suggest that MVH proteins function in these components of nuage. MVH protein-positive structures other than CBs disappeared during meiosis and CB appeared first in early spermatids. The results suggest that the formation of nuage is discontinued between spermatocytes and spermatids. The formation of nuage in spermatocytes and of CB in spermatids is discussed.

Smed-SmB, a member of the LSm protein superfamily, is essential for chromatoid body organization and planarian stem cell proliferation

Smed-SmB, a member of the LSm protein superfamily, is essential for chromatoid body organization and planarian stem cell proliferation

Mago, a vertebrate homolog of Drosophila Mago nashi protein, is a component of the chromatoid body in the cytoplasm of the postmeiotic spermatid

Post-transcriptional regulations play a crucial role during spermatogenesis of the vertebrates. Chromatoid body (CB) is a characteristic spermatid organelle that is supposed to exert its role in post-transcriptional processes, but its real functions remain largely unknown. Here we report identification of Mago from the rice field eel, and show its evolutionary conservation, differential expression and localization during gonadal transformation. The Mago interacts with Y14, which may facilitate nuclear export of both proteins in the Sertoli cells. Importantly, we have determined Mago as a novel component of the CB in the cytoplasm of the developing spermatid. Addition of Mago to the component list of the CB undoubtedly provides new clue as to the functions of the CB during spermatogenesis in the vertebrates.

Different requirements for conserved post-transcriptional regulators in planarian regeneration and stem cell maintenance

Planarian regeneration depends on the presence and precise regulation of pluripotent adult somatic stem cells named neoblasts, which differentiate to replace cells of any missing tissue. A characteristic feature of neoblasts is the presence of large perinuclear nonmembranous organelles named “chromatoid bodies”, which are comparable to ribonucleoprotein structures found in germ cells of organisms across different phyla. In order to better understand regulation of gene expression in neoblasts, and potentially the function and composition of chromatoid bodies, we characterized homologues to known germ and soma ribonucleoprotein granule components from other organisms and analyzed their function during regeneration of the planarian Dugesia japonica. Expression in neoblasts was detected for 49 of 55 analyzed genes, highlighting the prevalence of post-transcriptional regulation in planarian stem cells. RNAi-mediated knockdown of two factors [ ago-2 and bruli] lead to loss of neoblasts, and consequently loss of regeneration, corroborating with results previously reported for a bruli ortholog in the planarian Schmidtea mediterranea (Guo et al., 2006). Conversely, depletion mRNA turnover factors [ edc-4 or upf-1], exoribonucleases [ xrn-1 or xrn-2], or DEAD box RNA helicases [ Djcbc-1 or vas-1] inhibited planarian regeneration, but did not reduce neoblast proliferation or abundance. We also found that depletion of cap-dependent translation initiation factors eIF-3A or eIF-2A interrupted cell cycle progression outside the M-phase of mitosis. Our results show that a set of post-transcriptional regulators is required to maintain the stem cell identity in neoblasts, while another facilitates proper differentiation. We propose that planarian neoblasts maintain pluripotency by employing mechanisms of post-transcriptional regulation exhibited in germ cells and early development of most metazoans.

Smed-SmB, a member of the LSm protein superfamily, is essential for chromatoid body organization and planarian stem cell proliferation

Planarians are an ideal model system to study in vivo the dynamics of adult pluripotent stem cells. However, our knowledge of the factors necessary for regulating the 'stemness' of the neoblasts, the adult stem cells of planarians, is sparse. Here, we report on the characterization of the first planarian member of the LSm protein superfamily, Smed-SmB, which is expressed in stem cells and neurons in Schmidtea mediterranea. LSm proteins are highly conserved key players of the splicing machinery. Our study shows that Smed-SmB protein, which is localized in the nucleus and the chromatoid body of stem cells, is required to safeguard the proliferative ability of the neoblasts. The chromatoid body, a cytoplasmatic ribonucleoprotein complex, is an essential regulator of the RNA metabolism required for the maintenance of metazoan germ cells. However, planarian neoblasts and neurons also rely on its functions. Remarkably, Smed-SmB dsRNA-mediated knockdown results in a rapid loss of organization of the chromatoid body, an impairment of the ability to post-transcriptionally process the transcripts of Smed-CycB, and a severe proliferative failure of the neoblasts. This chain of events leads to a quick depletion of the neoblast pool, resulting in a lethal phenotype for both regenerating and intact animals. In summary, our results suggest that Smed-SmB is an essential component of the chromatoid body, crucial to ensure a proper RNA metabolism and essential for stem cell proliferation.