Drosophila rae1 is required for male meiosis and spermatogenesis

Apple Polyphenol Diet Extends Lifespan, Slows down Mitotic Rate and Reduces Morphometric Parameters in Drosophila Melanogaster: A Comparison between Three Different Apple Cultivars

Plant-derived polyphenols exhibit beneficial effects on physiological and pathological processes, including cancer and neurodegenerative disorders, mainly because of their antioxidant activity. Apples are highly enriched in these compounds, mainly in their peel. The Tuscia Red (TR) apple variety exhibits the peculiar characteristic of depositing high quantities of polyphenols in the pulp, the edible part of the fruit. Since polyphenols, as any natural product, cannot be considered a panacea per se, in this paper, we propose to assess the biological effects of TR flesh extracts, in comparison with two commercial varieties, in a model system, the insect Drosophila melanogaster, largely recognized as a reliable system to test the in vivo effects of natural and synthetic compounds. We performed a comparative, qualitative and quantitative analysis of the polyphenol compositions of the three cultivars and found that TR flesh shows the highest content of polyphenols, and markedly, anthocyanins. Then, we focused on their effects on a panel of physiological, morphometrical, cellular and behavioral phenotypes in wild-type D. melanogaster. We found that all the apple polyphenol extracts showed dose-dependent effects on most of the phenotypes we considered. Remarkably, all the varieties induced a strong relenting of the cell division rate.

Proteolysis in Reproduction: Lessons From Gene-Modified Organism Studies

The physiological roles of proteolysis are not limited to degrading unnecessary proteins. Proteolysis plays pivotal roles in various biological processes through cleaving peptide bonds to activate and inactivate proteins including enzymes, transcription factors, and receptors. As a wide range of cellular processes is regulated by proteolysis, abnormalities or dysregulation of such proteolytic processes therefore often cause diseases. Recent genetic studies have clarified the inclusion of proteases and protease inhibitors in various reproductive processes such as development of gonads, generation and activation of gametes, and physical interaction between gametes in various species including yeast, animals, and plants. Such studies not only clarify proteolysis-related factors but the biological processes regulated by proteolysis for successful reproduction. Here the physiological roles of proteases and proteolysis in reproduction will be reviewed based on findings using gene-modified organisms.

Mask, the Drosophila ankyrin repeat and KH domain-containing protein, affects microtubule stability

Proper regulation of microtubule (MT) stability and dynamics is vital for essential cellular processes, including axonal transportation and synaptic growth and remodeling in neurons. In the present study, we demonstrate that the Drosophila ankyrin repeat and KH domain-containing protein Mask negatively affects MT stability in both larval muscles and motor neurons. In larval muscles, loss-of-function of mask increases MT polymer length, and in motor neurons, loss of mask function results in overexpansion of the presynaptic terminal at the larval neuromuscular junctions (NMJs). mask genetically interacts with stathmin (stai), a neuronal modulator of MT stability, in the regulation of axon transportation and synaptic terminal stability. Our structure–function analysis of Mask revealed that its ankyrin repeats domain-containing N-terminal portion is sufficient to mediate Mask's impact on MT stability. Furthermore, we discovered that Mask negatively regulates the abundance of the MT-associated protein Jupiter in motor neuron axons, and that neuronal knocking down of Jupiter partially suppresses mask loss-of-function phenotypes at the larval NMJs. Taken together, our studies demonstrate that Mask is a novel regulator for MT stability, and such a role of Mask requires normal function of Jupiter.

Summary: Mask is a novel regulator of MT stability in Drosophila. Mask shows prominent interplay with two important modulators of MT, Tau and Stathmin (Stai), whose mutations are related to human diseases.

Ribonucleic Acid Export 1 Is a Kinetochore-Associated Protein That Participates in Chromosome Alignment in Mouse Oocytes

Ribonucleic acid export 1 (Rae1) is an important nucleoporin that participates in mRNA export during the interphase of higher eukaryotes and regulates the mitotic cell cycle. In this study, small RNA interference technology was used to knockdown Rae1, and immunofluorescence, immunoblotting, and chromosome spreading were used to study the role of Rae1 in mouse oocyte meiotic maturation. We found that Rae1 is a crucial regulator of meiotic maturation of mouse oocytes. After the resumption of meiosis (GVBD), Rae1 was concentrated on the kinetochore structure. The knockdown of Rae1 by a specific siRNA inhibited GVBD progression at 2 h, finally leading to a decreased 14 h polar body extrusion (PBE) rate. However, a comparable 14 h PBE rate was found in the control, and the Rae1 knockdown groups that had already undergone GVBD. Furthermore, we found elevated PBE after 9.5 h in the Rae1 knockdown oocytes. Further analysis revealed that Rae1 depletion significantly decreased the protein level of securin. In addition, we detected weakened kinetochore–microtubule (K-MT) attachments, misaligned chromosomes, and an increased incidence of aneuploidy in the Rae1 knockdown oocytes. Collectively, we propose that Rae1 modulates securin protein levels, which contribute to chromosome alignment, K-MT attachments, and aneuploidy in meiosis.

The tumor suppressor archipelago E3 ligase is required for spermatid differentiation in Drosophila testis

The human orthologue of the tumor suppressor protein FBW7 is encoded by the Drosophila archipelago (ago) gene. Ago is an F-box protein that gives substrate specificity to its SCF ubiquitin ligase complex. It has a central role in multiple biological processes in a tissue-specific manner such as cell proliferation, cellular differentiation, hypoxia-induced gene expression. Here we present a previously unknown tissue-specific role of Ago in spermatid differentiation. We identified a classical mutant of ago which is semi-lethal and male-sterile. During the characterization of ago function in testis, we found that ago plays role in spermatid development, following meiosis. We confirmed spermatogenesis defects by silencing ago by RNAi in testes. The ago mutants show multiple abnormalities in elongating and elongated spermatids, including aberration of the cyst morphology, malformed mitochondrial structures, and individualization defects. Additionally, we determined the subcellular localization of Ago protein with mCherry-Ago transgene in spermatids. Our findings highlight the potential roles of Ago in different cellular processes of spermatogenesis, like spermatid individualization, and regulation of mitochondrial morphology.

Astrocytes close a motor circuit critical period

Critical periods-brief intervals during which neural circuits can be modified by activity-are necessary for proper neural circuit assembly. Extended critical periods are associated with neurodevelopmental disorders; however, the mechanisms that ensure timely critical period closure remain poorly understood^1,2. Here we define a critical period in a developing Drosophila motor circuit and identify astrocytes as essential for proper critical period termination. During the critical period, changes in activity regulate dendrite length, complexity and connectivity of motor neurons. Astrocytes invaded the neuropil just before critical period closure³, and astrocyte ablation prolonged the critical period. Finally, we used a genetic screen to identify astrocyte-motor neuron signalling pathways that close the critical period, including Neuroligin-Neurexin signalling. Reduced signalling destabilized dendritic microtubules, increased dendrite dynamicity and impaired locomotor behaviour, underscoring the importance of critical period closure. Previous work defined astroglia as regulators of plasticity at individual synapses⁴; we show here that astrocytes also regulate motor circuit critical period closure to ensure proper locomotor behaviour.

Expression profiling of WD40 family genes including DDB1- and CUL4- associated factor (DCAF) genes in mice and human suggests important regulatory roles in testicular development and spermatogenesis

BACKGROUND

The WD40-repeat containing proteins, including DDB1-CUL4-associated factors (DCAFs), are abundant and conserved proteins that play important roles in different cellular processes including spermatogenesis. DCAFs are subset of WD40 family proteins that contain WDxR motif and have been proposed to function as substrate receptor for Cullin4-RING-based E3 ubiquitin ligase complexes to recruit diverse proteins for ubiquitination, a vital process in spermatogenesis. Large number of WD40 genes has been identified in different species including mouse and human. However, a systematic expression profiling of WD40 genes in different tissues of mouse and human has not been investigated. We hypothesize that large number of WD40 genes may express highly or specifically in the testis, where their expression is uniquely regulated during testis development and spermatogenesis. Therefore, the objective of this study is to mine and characterize expression patterns of WD40 genes in different tissues of mouse and human with particular emphasis on DCAF genes expressions during mouse testicular development.

RESULTS

Publically available RNA sequencing (RNA seq) data mining identified 347 and 349 WD40 genes in mouse and human, respectively. Hierarchical clustering and heat map analyses of RNA seq datasets revealed differential expression patterns of WD40 genes with around 60-73% of the genes were highly or specifically expressed in testis. Similarly, around 74-83% of DCAF genes were predominantly or specifically expressed in testis. Moreover, WD40 genes showed distinct expression patterns during embryonic and postnatal testis development in mice. Finally, different germ cell populations of testis showed specific patterns of WD40 genes expression. Predicted gene ontology analyses revealed more than 80% of these proteins are implicated in cellular, metabolic, biological regulation and cell localization processes.

CONCLUSIONS

We have identified large number of WD40 family genes that are highly or specifically expressed in the testes of mouse and human. Moreover, WD40 genes have distinct expression patterns during embryonic and postnatal development of the testis in mice. Further, different germ cell populations within the testis showed specific patterns of WD40 genes expression. These results provide foundation for further research towards understanding the functional genomics and molecular mechanisms of mammalian testis development and spermatogenesis.

Role of Nucleoporins and Transport Receptors in Cell Differentiation

Bidirectional molecular movements between the nucleus and cytoplasm take place through nuclear pore complexes (NPCs) embedded in the nuclear membrane. These macromolecular structures are composed of several nucleoporins, which form seven different subcomplexes based on their biochemical affinity. These nucleoporins are integral components of the complex, not only allowing passive transport but also interacting with importin, exportin, and other molecules that are required for transport of protein in various cellular processes. Transport of different proteins is carried out either dependently or independently on transport receptors. As well as facilitating nucleocytoplasmic transport, nucleoporins also play an important role in cell differentiation, possibly by their direct gene interaction. This review will cover the general role of nucleoporins (whether its dependent or independent) and nucleocytoplasmic transport receptors in cell differentiation.

Nuclear Export of Cyclin B Mediated by the Nup62 Complex Is Required for Meiotic Initiation in Drosophila Males

BACKGROUND

The central channel of the nuclear pore complex plays an important role in the selective transport of proteins between the nucleus and cytoplasm. Previous studies have demonstrated that the depletion of the Nup62 complex, constructing the nuclear pore channel in premeiotic Drosophila cells, resulted in the absence of meiotic cells. We attempted to understand the mechanism underlying the cell cycle arrest before meiosis.

METHODS

We induced dsRNAs against the nucleoporin mRNAs using the Gal4/UAS system in Drosophila.

RESULTS

The cell cycle of the Nup62-depleted cells was arrested before meiosis without CDK1 activation. The ectopic over-expression of CycB, but not constitutively active CDK1, resulted in partial rescue from the arrest. CycB continued to exist in the nuclei of Nup62-depleted cells and cells depleted of exportin encoded by emb. Protein complexes containing CycB, Emb, and Nup62 were observed in premeiotic spermatocytes. CycB, which had temporally entered the nucleus, was associated with Emb, and the complex was transported back to the cytoplasm through the central channel, interacting with the Nup62 complex. Conclusion: We proposed that CycB is exported with Emb through the channel interacting with the Nup62 complex before the onset of meiosis. The nuclear export ensures the modification and formation of sufficient CycB-CDK1 in the cytoplasm.

The Natural Compound Climacostol as a Prodrug Strategy Based on pH Activation for Efficient Delivery of Cytotoxic Small Agents

We synthesized and characterized MOMO as a new small molecule analog of the cytotoxic natural product climacostol efficiently activated in mild extracellular acidosis. The synthesis of MOMO had a key step in the Wittig olefination for the construction of the carbon-carbon double bond in the alkenyl moiety of climacostol. The possibility of obtaining the target (Z)-alkenyl MOMO derivative in very good yield and without presence of the less active (E)-diastereomer was favored from the methoxymethyl ether (MOM)-protecting group of hydroxyl functions in aromatic ring of climacostol aldehyde intermediate. Of interest, the easy removal of MOM-protecting group in a weakly acidic environment allowed us to obtain a great quantity of climacostol in biologically active (Z)-configuration. Results obtained in free-living ciliates that share the same micro-environment of the climacostol natural producer Climacostomum virens demonstrated that MOMO is well-tolerated in a physiological environment, while its cytotoxicity is rapidly and efficiently triggered at pH 6.3. In addition, the cytostatic vs. cytotoxic effects of acidified-MOMO can be modulated in a dose-dependent manner. In mouse melanoma cells, MOMO displayed a marked pH-sensitivity since its cytotoxic and apoptotic effects become evident only in mild extracellular acidosis. Data also suggested MOMO being preferentially activated in the unique extra-acidic microenvironment that characterizes tumoural cells. Finally, the use of the model organism Drosophila melanogaster fed with an acidic diet supported the efficient activity and oral delivery of MOMO molecule in vivo. MOMO affected oviposition of mating adults and larvae eclosion. Reduced survival of flies was due to lethality during the larval stages while emerging larvae retained their ability to develop into adults. Interestingly, the gut of eclosed larvae exhibited an extended damage (cell death by apoptosis) and the brain tissue was also affected (reduced mitosis), demonstrating that orally activated MOMO efficiently targets different tissues of the developing fly. These results provided a proof-of-concept study on the pH-dependence of MOMO effects. In this respect, MOM-protection emerges as a potential prodrug strategy which deserves to be further investigated for the generation of efficient pH-sensitive small organic molecules as pharmacologically active cytotoxic compounds.

Drosophila Pif1A is essential for spermatogenesis and is the homolog of human CCDC157, a gene associated with idiopathic NOA

The dynamic process of spermatogenesis shows little variation between invertebrate models such as Drosophila, and vertebrate models such as mice and rats. In each case, germ stem cells undergo mitotic division to proliferate and then continue, via meiosis, through various stages of elongation and individualization from spermatogonia to spermatid to finally to form mature sperm. Mature sperm are then stored in the seminal vesicles for fertilization. Errors in any of these stages can lead to male infertility. Here, we identify that Drosophila Pif1A acts as a key regulator for sperm individualization. Loss of Pif1A leads to male sterility associated with irregular individualization complex and empty seminal vesicles without mature sperm. Pif1A is highly expressed in the testes of mated male adult flies and the Pif1A protein is expressed at a higher level in male than in female flies. Pif1A is homologous to mammalian coiled-coil domain-containing protein 157 (CCDC157), which is also enriched in the testes of humans and mice. Human CCDC157, with unknown function, was identified to be downregulated in men with idiopathic non-obstructive azoospermia (NOA). We map the function of Drosophila Pif1A during spermatogenesis, showing that Pif1A is essential for spermatide individualization and involved in the regulation of the lipid metabolism genes. Our findings might be applicable for studying the function of CCDC157 in spermatogenesis and other aspects of human male fertility.

RAE1 promotes BMAL1 shuttling and regulates degradation and activity of CLOCK: BMAL1 heterodimer

Circadian rhythm is an autoregulatory rhythm, which is sustained by various mechanisms. The nucleocytoplasmic shuttling of BMAL1 is essential for CLOCK translocation between cytoplasm and nucleus and maintenance of the correct pace of the circadian clock. Here we showed that RAE1 and NUP98 can promote the degradation of BMAL1 and CLOCK. Knockdown of RAE1 and NUP98 suppressed BMAL1 shuttling, leading to cytoplasm accumulation of CLOCK. Furthermore, Chip assay showed that knockdown of RAE1 and NUP98 can enhance the interaction between CLOCK: BMAL1 and E-box region in the promoters of Per2 and Cry1 while reducing its transcription activation activity. Our present study firstly revealed that RAE1 and NUP98 are critical regulators for BMAL1 shuttling.

Phenotypic characterization of diamond (dind), a Drosophila gene required for multiple aspects of cell division

Many genes are required for the assembly of the mitotic apparatus and for proper chromosome behavior during mitosis and meiosis. A fruitful approach to elucidate the mechanisms underlying cell division is the accurate phenotypic characterization of mutations in these genes. Here, we report the identification and characterization of diamond (dind), an essential Drosophila gene required both for mitosis of larval brain cells and for male meiosis. Larvae homozygous for any of the five EMS-induced mutations die in the third-instar stage and exhibit multiple mitotic defects. Mutant brain cells exhibit poorly condensed chromosomes and frequent chromosome breaks and rearrangements; they also show centriole fragmentation, disorganized mitotic spindles, defective chromosome segregation, endoreduplicated metaphases, and hyperploid and polyploid cells. Comparable phenotypes occur in mutant spermatogonia and spermatocytes. The dind gene encodes a non-conserved protein with no known functional motifs. Although the Dind protein exhibits a rather diffuse localization in both interphase and mitotic cells, fractionation experiments indicate that some Dind is tightly associated with the chromatin. Collectively, these results suggest that loss of Dind affects chromatin organization leading to defects in chromosome condensation and integrity, which in turn affect centriole stability and spindle assembly. However, our results do not exclude the possibility that Dind directly affects some behaviors of the spindle and centrosomes.

Mitochondrial Epigenetics and Environmental Exposure

The rising toll of chronic and debilitating diseases brought about by the exposure to an ever expanding number of environmental pollutants and socio-economic factors is calling for action. The understanding of the molecular mechanisms behind the effects of environmental exposures can lead to the development of biomarkers that can support the public health fields of both early diagnosis and intervention to limit the burden of environmental diseases. The study of mitochondrial epigenetics carries high hopes to provide important biomarkers of exposure and disease. Mitochondria are in fact on the frontline of the cellular response to the environment. Modifications of the epigenetic factors regulating the mitochondrial activity are emerging as informative tools that can effectively report on the effects of the environment on the phenotype. Here, we will discuss the emerging field of mitochondrial epigenetics. This review describes the main epigenetic phenomena that modify the activity of the mitochondrial DNA including DNA methylation, long and short non-coding RNAs. We will discuss the unique pattern of mitochondrial DNA methylation, describe the challenges of correctly measuring it, and report on the existing studies that have analysed the correlation between environmental exposures and mitochondrial DNA methylation. Finally, we provide a brief account of the therapeutic approaches targeting mitochondria currently under consideration.

AtRAE1 is involved in degradation of ABA receptor RCAR1 and negatively regulates ABA signalling in Arabidopsis

The phytohormone abscisic acid (ABA) plays an important role in regulating plant growth, development, and adaption to various environmental stresses. Regulatory components of ABA receptors (RCARs, also known as PYR/PYLs) sense ABA and initiate ABA signalling through inhibiting the activities of protein phosphatase 2C in Arabidopsis. However, the way in which ABA receptors are regulated is not well known. A DWD protein AtRAE1 (for RNA export factor 1 in Arabidopsis), which may act as a substrate receptor of CUL4-DDB1 E3 ligase, is an interacting partner of RCAR1/PYL9. The physical interaction between RCAR1 and AtRAE1 is confirmed in vitro and in vivo. Overexpression of AtRAE1 in Arabidopsis causes reduced sensitivity of plants to ABA, whereas suppression of AtRAE1 causes increased sensitivity to ABA. Analysis of protein stability demonstrates that RCAR1 is ubiquitinated and degraded in plant cells and AtRAE1 regulates the degradation speed of RCAR1. Our findings indicate that AtRAE1 likely participates in ABA signalling through regulating the degradation of ABA receptor RCAR1.

The Hippo Pathway: A Master Regulatory Network Important in Development and Dysregulated in Disease

The Hippo Pathway is a master regulatory network that regulates proliferation, cell growth, stemness, differentiation, and cell death. Coordination of these processes by the Hippo Pathway throughout development and in mature organisms in response to diverse external and internal cues plays a role in morphogenesis, in controlling organ size, and in maintaining organ homeostasis. Given the importance of these processes, the Hippo Pathway also plays an important role in organismal health and has been implicated in a variety of diseases including eye disease, cardiovascular disease, neurodegeneration, and cancer. This review will focus on Drosophila reports that identified the core components of the Hippo Pathway revealing specific downstream biological outputs of this complicated network. A brief description of mammalian reports will complement review of the Drosophila studies. This review will also survey upstream regulation of the core components with a focus on feedback mechanisms.

The Hippo Pathway Targets Rae1 to Regulate Mitosis and Organ Size and to Feed Back to Regulate Upstream Components Merlin, Hippo, and Warts

Hippo signaling acts as a master regulatory pathway controlling growth, proliferation, and apoptosis and also ensures that variations in proliferation do not alter organ size. How the pathway coordinates restricting proliferation with organ size control remains a major unanswered question. Here we identify Rae1 as a highly-conserved target of the Hippo Pathway integrating proliferation and organ size. Genetic and biochemical studies in Drosophila cells and tissues and in mammalian cells indicate that Hippo signaling promotes Rae1 degradation downstream of Warts/Lats. In proliferating cells, Rae1 loss restricts cyclin B levels and organ size while Rae1 over-expression increases cyclin B levels and organ size, similar to Hippo Pathway over-activation or loss-of-function, respectively. Importantly, Rae1 regulation by the Hippo Pathway is crucial for its regulation of cyclin B and organ size; reducing Rae1 blocks cyclin B accumulation and suppresses overgrowth caused by Hippo Pathway loss. Surprisingly, in addition to suppressing overgrowth, reducing Rae1 also compromises survival of epithelial tissue overgrowing due to loss of Hippo signaling leading to a tissue “synthetic lethality” phenotype. Excitingly, Rae1 plays a highly conserved role to reduce the levels and activity of the Yki/YAP oncogene. Rae1 increases activation of the core kinases Hippo and Warts and plays a post-transcriptional role to increase the protein levels of the Merlin, Hippo, and Warts components of the pathway; therefore, in addition to Rae1 coordinating organ size regulation with proliferative control, we propose that Rae1 also acts in a feedback circuit to regulate pathway homeostasis.

Exquisite control of organ size is critical during animal development and its loss results in pathological conditions. The Hippo Tumor Suppressor Pathway coordinates regulation of proliferation, growth, apoptosis, and autophagy to determine and maintain precise control of organ size. However, the genes responsible for Hippo-mediated regulation of mitosis or coordination of proliferation within organ size control have evaded characterization. Here, we describe Rae1, an essential WD-repeat containing protein, as a new organ size regulator. By genetic analysis, we show that Rae1 acts downstream of the Hippo Pathway to regulate mitotic cyclins and organ size. In contexts where organ size control is lost by compromised Hippo signaling, we show that there is a requirement for Rae1 that is distinct from the requriement for Yki: reducing Yki levels causes suppression of overgrowth, while reducing Rae1 levels dramatically compromises the survival of Hippo-deficient tissue. Lastly, our studies of Rae1 uncovered a potential post-transcriptional feedback loop that reinforces Yorkie-mediated transcriptional feedback for the Hippo Pathway.

Confocal Analysis of Nuclear Lamina Behavior during Male Meiosis and Spermatogenesis in Drosophila melanogaster

Lamin family proteins are structural components of a filamentous framework, the nuclear lamina (NL), underlying the inner membrane of nuclear envelope. The NL not only plays a role in nucleus mechanical support and nuclear shaping, but is also involved in many cellular processes including DNA replication, gene expression and chromatin positioning. Spermatogenesis is a very complex differentiation process in which each stage is characterized by nuclear architecture dramatic changes, from the early mitotic stage to the sperm differentiation final stage. Nevertheless, very few data are present in the literature on the NL behavior during this process. Here we show the first and complete description of NL behavior during meiosis and spermatogenesis in Drosophila melanogaster. By confocal imaging, we characterized the NL modifications from mitotic stages, through meiotic divisions to sperm differentiation with an anti-laminDm0 antibody against the major component of the Drosophila NL. We observed that continuous changes in the NL structure occurred in parallel with chromatin reorganization throughout the whole process and that meiotic divisions occurred in a closed context. Finally, we analyzed NL in solofuso meiotic mutant, where chromatin segregation is severely affected, and found the strict correlation between the presence of chromatin and that of NL.

Functional significance of nuclear export and mRNA binding of meiotic regulator Spo5 in fission yeast

Background

Meiotic cells undergo two rounds of nuclear division and generate gametes. Previous studies have indicated that a number of transcription factors modulate the transcriptome in successive waves during meiosis and spore formation in fission yeast. However, the mechanisms underlying the post-transcriptional regulation in meiosis are not fully understood. The fission yeast spo5⁺ gene encodes a meiosis-specific RNA-binding protein, which is required for the progression of meiosis II and spore formation. However, the target RNA molecules of Spo5 are yet to be identified. Characterization of meiosis-specific RNA-binding proteins will provide insight into how post-transcriptional regulation influence gene expression during sexual differentiation.

Results

To assess the functional significance of RNA-recognition motifs (RRMs) of Spo5, we constructed a series of new spo5 truncated mutants and previously reported spo5 missense mutants. In addition, we isolated novel spo5 missense mutants. The phenotypic characteristics of these mutants indicated that the RRMs are essential for both the localization and function of the protein. Interestingly, Spo5 is exported from the nucleus to the cytoplasm via the Rae1-dependent mRNA export pathway, but is unlikely to be involved in global mRNA export. Furthermore, cytoplasmic localization of Spo5 is important for its function, which suggests the involvement of Spo5 in post-transcriptional regulation. We identified pcr1⁺ mRNA as one of the critical targets of Spo5. The pcr1⁺ gene encodes an activating transcription factor/cAMP response element binding (ATF/CREB) transcription factor family. Among the four family members, namely Pcr1, Atf1, Atf21, and Atf31, only the mRNA encoding Pcr1 binds to Spo5.

Conclusions

Spo5 is exported from the nucleus with mRNAs via the Rae1-dependent pathway. RRMs are necessary for this process and also for the function of Spo5 after the nuclear export. Spo5 appears to influence the activity of pcr1⁺ mRNA, and the mechanism of how Spo5 stimulates the mRNA to promote the progression of meiosis II and spore formation remains an intriguing question for future research.