Promising aberrant DNA methylation marker to predict gastric cancer development in individuals with family history and long-term effects of H. pylori eradication on DNA methylation.

OBJECTIVE: It remains unknown whether individuals with a family history (FH) of gastric cancer (GC) are associated with aberrant DNA methylation. The aim of this study was to investigate the association between aberrant DNA methylation and FH of GC. DESIGN: Using quantitative MethyLight assay, MOS, miR124a-3, NKX6-1, EMX1, CDH1, and TWIST1 methylation levels in the noncancerous gastric mucosa was compared between subjects with and without FH based on GC and Helicobacter pylori (Hp) infection. Changes in the methylation levels were evaluated over time after Hp eradication. RESULTS: In Hp-positive GC patients, MOS (P < 0.001), CDH1 (P < 0.001), and TWIST1 (P = 0.004) methylation were decreased in subjects with FH (n = 64) than in those without FH (n = 58). In Hp-positive controls, MOS methylation was lower in subjects with FH (n = 73) than in those without FH (n = 50) (P = 0.042), while miR124a-3 (P = 0.006), NKX6-1 (P < 0.001), and CDH1 (P < 0.001) methylation were higher in subjects with FH. CDH1 methylation constantly decreased from 2 years in GC patients and 3-4 years in controls after Hp eradication (all P < 0.001). A persistent decrease in methylation over time was not observed in other genes after eradication. CONCLUSION: The methylation of MOS and CDH1 provided an association between aberrant DNA methylation and gastric carcinogenesis in FH of GC, a useful marker for GC risk in individuals with FH. Furthermore, CDH1 methylation decreased after Hp eradication.

Heterogeneous pattern of DNA methylation in developmentally important genes correlates with its chromatin conformation.

BACKGROUND: DNA methylation is a major epigenetic modification, playing a crucial role in the development and differentiation of higher organisms. DNA methylation is also known to regulate transcription by gene repression. Various developmental genes such as c-mos, HoxB5, Sox11, and Sry show tissue-specific gene expression that was shown to be regulated by promoter DNA methylation. The aim of the present study is to investigate the establishment of chromatin marks (active or repressive) in relation to heterogeneous methylation in the promoter regions of these developmentally important genes. RESULTS: Chromatin-immunoprecipitation (ChIP) assays were performed to immuno-precipitate chromatin by antibodies against both active (H3K4me3) and repressive (H3K9me3) chromatin regions. The analysis of ChIP results showed that both the percentage input and fold enrichment of activated chromatin was higher in tissues expressing the respective genes as compared to the tissues not expressing the same set of genes. This was true for all the genes selected for the study (c-mos, HoxB5, Sox11, and Sry). These findings illustrate that inconsistent DNA methylation patterns (sporadic, mosaic and heterogeneous) may also influence gene regulation, thereby resulting in the modulation of chromatin conformation. CONCLUSIONS: These findings illustrate that various patterns of DNA methylation (asynchronous, mosaic and heterogeneous) correlates with chromatin modification, resulting in the gene regulation.

Multipolar mitosis of tetraploid cells: inhibition by p53 and dependency on Mos.

Tetraploidy can constitute a metastable intermediate between normal diploidy and oncogenic aneuploidy. Here, we show that the absence of p53 is not only permissive for the survival but also for multipolar asymmetric divisions of tetraploid cells, which lead to the generation of aneuploid cells with a near-to-diploid chromosome content. Multipolar mitoses (which reduce the tetraploid genome to a sub-tetraploid state) are more frequent when p53 is downregulated and the product of the Mos oncogene is upregulated. Mos inhibits the coalescence of supernumerary centrosomes that allow for normal bipolar mitoses of tetraploid cells. In the absence of p53, Mos knockdown prevents multipolar mitoses and exerts genome-stabilizing effects. These results elucidate the mechanisms through which asymmetric cell division drives chromosomal instability in tetraploid cells.

dsRNA expression in the mouse elicits RNAi in oocytes and low adenosine deamination in somatic cells.

Double-stranded RNA (dsRNA) can enter different pathways in mammalian cells, including sequence-specific RNA interference (RNAi), sequence-independent interferon (IFN) response and editing by adenosine deaminases. To study the routing of dsRNA to these pathways in vivo, we used transgenic mice ubiquitously expressing from a strong promoter, an mRNA with a long hairpin in its 3'-UTR. The expressed dsRNA neither caused any developmental defects nor activated the IFN response, which was inducible only at high expression levels in cultured cells. The dsRNA was poorly processed into siRNAs in somatic cells, whereas, robust RNAi effects were found in oocytes, suggesting that somatic cells lack some factor(s) facilitating siRNA biogenesis. Expressed dsRNA did not cause transcriptional silencing in trans. Analysis of RNA editing revealed that a small fraction of long dsRNA is edited. RNA editing neither prevented the cytoplasmic localization nor processing into siRNAs. Thus, a long dsRNA structure is well tolerated in mammalian cells and is mainly causing a robust RNAi response in oocytes.

Rampant horizontal transfer of SPIN transposons in squamate reptiles.

Transposable elements (TEs) are highly abundant in the genome and capable of mobility, two properties that make them particularly prone to transfer horizontally between organisms. Although the impact of horizontal transfer (HT) of TEs is well recognized in prokaryotes, the frequency of this phenomenon and its contribution to genome evolution in eukaryotes remain poorly appreciated. Here, we provide evidence that a DNA transposon called SPIN has colonized the genome of 17 species of reptiles representing nearly every major lineage of squamates, including 14 families of lizards, snakes, and amphisbaenians. Slot blot analyses indicate that SPIN has amplified to high copy numbers in most of these species, ranging from 2,000-28,000 copies per haploid genome. In contrast, we could not detect the presence of SPIN in any of the turtles (seven species from seven families) and crocodiles (four species) examined. Genetic distances between SPIN sequences from species belonging to different squamate families are consistently very low (average = 0.1), considering the deep evolutionary divergence of the families investigated (most are >100 My diverged). Furthermore, these distances fall below interfamilial distances calculated for two genes known to have evolved under strong functional constraint in vertebrates (RAG1, average = 0.24 and C-mos, average = 0.27). These data, combined with phylogenetic analyses, indicate that the widespread distribution of SPIN among squamates is the result of at least 13 independent events of HTs. Molecular dating and paleobiogeographical data suggest that these transfers took place during the last 50 My on at least three different continents (North America, South America and, Africa). Together, these results triple the number of known SPIN transfer events among tetrapods, provide evidence for a previously hypothesized transoceanic movement of SPIN transposons during the Cenozoic, and further underscore the role of HT in the evolution of vertebrate genomes.

Connecting cis-elements and trans-factors with mechanisms of developmental regulation of mRNA translation in meiotic and haploid mammalian spermatogenic cells.

mRNA-specific regulation of translational activity plays major roles in directing the development of meiotic and haploid spermatogenic cells in mammals. Although many RNA-binding proteins (RBPs) have been implicated in normal translational control and sperm development, little is known about the keystone of the mechanisms: the interactions of RBPs and microRNAs with cis-elements in mRNA targets. The problems in connecting factors and elements with translational control originate in the enormous complexity of post-transcriptional regulation in mammalian cells. This creates confusion as to whether factors have direct or indirect and large or small effects on the translation of specific mRNAs. This review argues that gene knockouts, heterologous systems, and overexpression of factors cannot provide convincing answers to these questions. As a result, the mechanisms involving well-studied mRNAs (Ddx4/Mvh, Prm1, Prm2, and Sycp3) and factors (DICER1, CPEB1, DAZL, DDX4/MVH, DDX25/GRTH, translin, and ELAV1/HuR) are incompletely understood. By comparison, mutations in elements can be used to define the importance of specific pathways in regulating individual mRNAs. However, few elements have been studied, because the only reliable system to analyze mutations in elements, transgenic mice, is considered impractical. This review describes advances that may facilitate identification of the direct targets of RBPs and analysis of mutations in cis-elements. The importance of upstream reading frames in the developmental regulation of mRNA translation in spermatogenic cells is also documented.

Prediction of the risk for gastric cancer using candidate methylation markers in the non-neoplastic gastric mucosae.

Aberrant DNA methylation is frequently found during gastric carcinogenesis. Recently, we identified potential methylation markers important for Helicobacter pylori-induced gastric carcinogenesis using an Illumina methylation chip assay. In this study, we evaluated the candidate genes as markers for gastric cancer (GC) in a large Korean population. DNA methylation of PTPN6, MOS, DCC, CRK, and VAV1 was evaluated in non-neoplastic gastric specimens using quantitative methylation-specific PCR in patients with GC (n = 207) and their age- and gender-matched controls (n = 207). Methylation levels in 125 GC samples were also compared. H. pylori infection status was categorized as negative, active, or past infection according to the results of endoscopy-based tests (CLOtest, histology, and culture), H. pylori serology, and serum pepsinogen test. In the controls, active H. pylori infection increased methylation levels in DCC, CRK, MOS, and VAV1 but decreased methylation levels in PTPN6 (all p < 0.05); the methylation levels in MOS remained increased in patients with past H. pylori infection compared to H. pylori-negative subjects (p < 0.001). Methylation levels in MOS in non-neoplastic gastric mucosae increased in the presence of GC, regardless of H. pylori infection status (p < 0.01). Methylation levels in all genes but DCC decreased significantly in GC specimens compared to neoplastic gastric mucosae (p < 0.01); however, methylation levels in GC tissues were not correlated with those in their background gastric mucosae. Hypomethylation of MOS in GC tissues was associated with tumour invasion, nodal metastasis, and undifferentiated histology (p < 0.05). To summarize, among the candidate genes, DNA methylation of MOS may reflect the duration of H. pylori exposure and may be a marker for the development of GC.

Phylogeny of the Asian Eutropis (Squamata: Scincidae) reveals an 'into India' endemic Indian radiation.

Recent generic rearrangement of the circumtropical distributed skink genus 'Mabuya' has raised a lot of debate. According to this molecular phylogeny based rearrangement, the tropical Asian members of this genus have been assigned to Eutropis. However, in these studies the Asian members of 'Mabuya' were largely sampled from Southeast (SE) Asia with very few species from Indian subcontinent. To test the validity of this assignment and to determine the evolutionary origin of Indian members of this group we sequenced one nuclear and two mitochondrial genes from most of the species from the Indian subregion. The nuclear and mitochondrial trees generated from these sequences confirmed the monophyly of the tropical Asian Eutropis. Furthermore, in the tree based on the combined mitochondrial and nuclear dataset an endemic Indian radiation was revealed that was nested within a larger Asian clade. Results of dispersal-vicariance analysis and molecular dating suggested an initial dispersal of Eutropis from SE Asia into India around 5.5-17 million years ago, giving rise to the extant members of the endemic Indian radiation. This initial dispersal was followed by two back dispersals from India into SE Asia. We also discuss the relationships within the endemic Indian radiation and its taxonomic implications.

Out of Asia: natricine snakes support the Cenozoic Beringian Dispersal Hypothesis.

Based on a combination of six mitochondrial gene fragments (12S RNA, cyt b, ND1, ND2, ND4 and CO1) and one nuclear gene (c-mos) from 22 genera we infer phylogenetic relationships among natricine snakes and examine the date and area of origin of these snakes. Our phylogenetic results indicate: (1) the subfamily Natricinae is strongly supported as monophyletic including a majority of extant genera, and a poorly known and previously unassigned species Trachischium monticola, (2) two main clades are inferred within Natricinae, one containing solely taxa from the Old World (OW) and the other comprising taxa from a monophyletic New World (NW) group with a small number of OW relatives. Within the first clade, the genera Xenochrophis and Amphiesma are apparently not monophyletic. Divergence dating and ancestral area estimation indicate that the natricines originated in tropical Asia during the later Eocene or the Oligocene. We recover two major dispersals events out of Asia, the first to Africa in the Oligocene (28 Ma) and the second to the Western Palearctic and the New World at 27 Ma. This date is consistent with the dispersal of numerous other OW groups into the NW.

Oncogene-induced senescence is part of the tumorigenesis barrier imposed by DNA damage checkpoints.

Recent studies have indicated the existence of tumorigenesis barriers that slow or inhibit the progression of preneoplastic lesions to neoplasia. One such barrier involves DNA replication stress, which leads to activation of the DNA damage checkpoint and thereby to apoptosis or cell cycle arrest, whereas a second barrier is mediated by oncogene-induced senescence. The relationship between these two barriers, if any, has not been elucidated. Here we show that oncogene-induced senescence is associated with signs of DNA replication stress, including prematurely terminated DNA replication forks and DNA double-strand breaks. Inhibiting the DNA double-strand break response kinase ataxia telangiectasia mutated (ATM) suppressed the induction of senescence and in a mouse model led to increased tumour size and invasiveness. Analysis of human precancerous lesions further indicated that DNA damage and senescence markers cosegregate closely. Thus, senescence in human preneoplastic lesions is a manifestation of oncogene-induced DNA replication stress and, together with apoptosis, provides a barrier to malignant progression.

Effects of epidermal growth factor and progesterone on development, ultrastructure and gene expression of bovine secondary follicles cultured in vitro.

The aims of this study were to investigate the effects of epidermal growth factor (EGF) and progesterone on the development, viability and the gene expression of bovine secondary follicle culture in vitro for 18 days. Secondary follicles (∼0.2 mm) were isolated from ovarian cortex and individually cultured at 38.5 °C, with 5% CO2 in air, for 18 days, in TCM-199+ (n = 63) alone (control medium) or supplemented with 10 ng/mL progesterone (n = 64), 10 ng/mL EGF (n = 61) or both EGF and progesterone (n = 66). The effects of these treatments on growth, antrum formation, viability, ultrastructure and mRNA levels for GDF-9, c-MOS, H1foo and cyclin B1 were evaluated, significantly different (p < 0.05). The results showed that there was a progressive increase in follicular diameter in all treatments, but only follicles cultured in medium supplemented with EGF had increased significantly in diameter when compared to follicles cultured in the control medium at the end of the culture period, significantly different (p < 0.05). A positive interaction between EGF and progesterone was not observed. In addition, the presence of EGF, progesterone or both in culture medium did not influence the rate of follicle survival and antrum formation. However, the presence of only progesterone in cultured medium increased the expression of mRNAs for GDF9 and cyclin B1 in oocytes. EGF also significantly increased the levels of mRNAs for cMOS and GDF9 when compared to follicles cultured in control medium. Ultrastructural analyzes showed that cultured follicles in all treatments maintained the integrity of granulosa cells. In conclusion, the EGF promotes the development of secondary follicles cultured in vitro for 18 days and increases the expression of cMOS and GDF9, while progesterone alone or in association with EGF have not a positive effect on follicular growth. However, progesterone increases the expression of GDF9 and cyclin B1 in oocytes.

A bacterial artificial chromosome library for the Australian saltwater crocodile (Crocodylus porosus) and its utilization in gene isolation and genome characterization.

BACKGROUND: Crocodilians (Order Crocodylia) are an ancient vertebrate group of tremendous ecological, social, and evolutionary importance. They are the only extant reptilian members of Archosauria, a monophyletic group that also includes birds, dinosaurs, and pterosaurs. Consequently, crocodilian genomes represent a gateway through which the molecular evolution of avian lineages can be explored. To facilitate comparative genomics within Crocodylia and between crocodilians and other archosaurs, we have constructed a bacterial artificial chromosome (BAC) library for the Australian saltwater crocodile, Crocodylus porosus. This is the first BAC library for a crocodile and only the second BAC resource for a crocodilian. RESULTS: The C. porosus BAC library consists of 101,760 individually archived clones stored in 384-well microtiter plates. NotI digestion of random clones indicates an average insert size of 102 kb. Based on a genome size estimate of 2778 Mb, the library affords 3.7 fold (3.7x) coverage of the C. porosus genome. To investigate the utility of the library in studying sequence distribution, probes derived from CR1a and CR1b, two crocodilian CR1-like retrotransposon subfamilies, were hybridized to C. porosus macroarrays. The results indicate that there are a minimum of 20,000 CR1a/b elements in C. porosus and that their distribution throughout the genome is decidedly non-random. To demonstrate the utility of the library in gene isolation, we probed the C. porosus macroarrays with an overgo designed from a C-mos (oocyte maturation factor) partial cDNA. A BAC containing C-mos was identified and the C-mos locus was sequenced. Nucleotide and amino acid sequence alignment of the C. porosus C-mos coding sequence with avian and reptilian C-mos orthologs reveals greater sequence similarity between C. porosus and birds (specifically chicken and zebra finch) than between C. porosus and squamates (green anole). CONCLUSION: We have demonstrated the utility of the Crocodylus porosus BAC library as a tool in genomics research. The BAC library should expedite complete genome sequencing of C. porosus and facilitate detailed analysis of genome evolution within Crocodylia and between crocodilians and diverse amniote lineages including birds, mammals, and other non-avian reptiles.

Mass survival of birds across the Cretaceous-Tertiary boundary: molecular evidence.

The extent of terrestrial vertebrate extinctions at the end of the Cretaceous is poorly understood, and estimates have ranged from a mass extinction to limited extinctions of specific groups. Molecular and paleontological data demonstrate that modern bird orders started diverging in the Early Cretaceous; at least 22 avian lineages of modern birds cross the Cretaceous-Tertiary boundary. Data for several other terrestrial vertebrate groups indicate a similar pattern of survival and, taken together, favor incremental changes during a Cretaceous diversification of birds and mammals rather than an explosive radiation in the Early Tertiary.

Transformation of mammalian cells by constitutively active MAP kinase kinase.

Mitogen-activated protein (MAP) kinase kinase (MAPKK) activates MAP kinase in a signal transduction pathway that mediates cellular responses to growth and differentiation factors. Oncogenes such as ras, src, raf, and mos have been proposed to transform cells by prolonging the activated state of MAPKK and of components downstream in the signaling pathway. To test this hypothesis, constitutively active MAPKK mutants were designed that had basal activities up to 400 times greater than that of the unphosphorylated wild-type kinase. Expression of these mutants in mammalian cells activated AP-1-regulated transcription. The cells formed transformed foci, grew efficiently in soft agar, and were highly tumorigenic in nude mice. These findings indicate that constitutive activation of MAPKK is sufficient to promote cell transformation.

MOS1 osmosensor of Metarhizium anisopliae is required for adaptation to insect host hemolymph.

Entomopathogenic fungi such as Metarhizium anisopliae infect insects by direct penetration of the cuticle, after which the fungus adapts to the high osmotic pressure of the hemolymph and multiplies. Here we characterize the M. anisopliae Mos1 gene and demonstrate that it encodes the osmosensor required for this process. MOS1 contains transmembrane regions and a C-terminal Src homology 3 domain similar to those of yeast osmotic adaptor proteins, and homologs of MOS1 are widely distributed in the fungal kingdom. Reverse transcription-PCR demonstrated that Mos1 is up-regulated in insect hemolymph as well as artificial media with high osmotic pressure. Transformants containing an antisense vector directed to the Mos1 mRNA depleted transcript levels by 80%. This produced selective alterations in regulation of genes involved in hyphal body formation, cell membrane stiffness, and generation of intracellular turgor pressure, suggesting that these processes are mediated by MOS1. Consistent with a role in stress responses, transcript depletion of Mos1 increased sensitivity to osmotic and oxidative stresses and to compounds that interfere with cell wall biosynthesis. It also disrupted developmental processes, including formation of appressoria and hyphal bodies. Insect bioassays confirmed that Mos1 knockdown significantly reduces virulence. Overall, our data show that M. anisopliae MOS1 mediates cellular responses to high osmotic pressure and subsequent adaptations to colonize host hemolymph.

Evolutionary history of burrowing asps (Lamprophiidae: Atractaspidinae) with emphasis on fang evolution and prey selection.

Atractaspidines are poorly studied, fossorial snakes that are found throughout Africa and western Asia, including the Middle East. We employed concatenated gene-tree analyses and divergence dating approaches to investigate evolutionary relationships and biogeographic patterns of atractaspidines with a multi-locus data set consisting of three mitochondrial (16S, cyt b, and ND4) and two nuclear genes (c-mos and RAG1). We sampled 91 individuals from both atractaspidine genera (Atractaspis and Homoroselaps). Additionally, we used ancestral-state reconstructions to investigate fang and diet evolution within Atractaspidinae and its sister lineage (Aparallactinae). Our results indicated that current classification of atractaspidines underestimates diversity within the group. Diversification occurred predominantly between the Miocene and Pliocene. Ancestral-state reconstructions suggest that snake dentition in these taxa might be highly plastic within relatively short periods of time to facilitate adaptations to dynamic foraging and life-history strategies.

The genus Coleodactylus (Sphaerodactylinae, Gekkota) revisited: a molecular phylogenetic perspective.

Nucleotide sequence data from a mitochondrial gene (16S) and two nuclear genes (c-mos, RAG-1) were used to evaluate the monophyly of the genus Coleodactylus, to provide the first phylogenetic hypothesis of relationships among its species in a cladistic framework, and to estimate the relative timing of species divergences. Maximum Parsimony, Maximum Likelihood and Bayesian analyses of the combined data sets retrieved Coleodactylus as a monophyletic genus, although weakly supported. Species were recovered as two genetically and morphological distinct clades, with C. amazonicus populations forming the sister taxon to the meridionalis group (C. brachystoma, C. meridionalis, C. natalensis, and C. septentrionalis). Within this group, C. septentrionalis was placed as the sister taxon to a clade comprising the rest of the species, C. meridionalis was recovered as the sister species to C. brachystoma, and C. natalensis was found nested within C. meridionalis. Divergence time estimates based on penalized likelihood and Bayesian dating methods do not support the previous hypothesis based on the Quaternary rain forest fragmentation model proposed to explain the diversification of the genus. The basal cladogenic event between major lineages of Coleodactylus was estimated to have occurred in the late Cretaceous (72.6+/-1.77 Mya), approximately at the same point in time than the other genera of Sphaerodactylinae diverged from each other. Within the meridionalis group, the split between C. septentrionalis and C. brachystoma+C. meridionalis was placed in the Eocene (46.4+/-4.22 Mya), and the divergence between C. brachystoma and C. meridionalis was estimated to have occurred in the Oligocene (29.3+/-4.33 Mya). Most intraspecific cladogenesis occurred through Miocene to Pliocene, and only for two conspecific samples and for C. natalensis could a Quaternary differentiation be assumed (1.9+/-1.3 Mya).

Mos 3' UTR regulatory differences underlie species-specific temporal patterns of Mos mRNA cytoplasmic polyadenylation and translational recruitment during oocyte maturation.

The Mos proto-oncogene is a critical regulator of vertebrate oocyte maturation. The maturation-dependent translation of Mos protein correlates with the cytoplasmic polyadenylation of the maternal Mos mRNA. However, the precise temporal requirements for Mos protein function differ between oocytes of model mammalian species and oocytes of the frog Xenopus laevis. Despite the advances in model organisms, it is not known if the translation of the human Mos mRNA is also regulated by cytoplasmic polyadenylation or what regulatory elements may be involved. We report that the human Mos 3' untranslated region (3' UTR) contains a functional cytoplasmic polyadenylation element (CPE) and demonstrate that the endogenous Mos mRNA undergoes maturation-dependent cytoplasmic polyadenylation in human oocytes. The human Mos 3' UTR interacts with the human CPE-binding protein and exerts translational control on a reporter mRNA in the heterologous Xenopus oocyte system. Unlike the Xenopus Mos mRNA, which is translationally activated by an early acting Musashi/polyadenylation response element (PRE)-directed control mechanism, the translational activation of the human Mos 3' UTR is dependent on a late acting CPE-dependent process. Taken together, our findings suggest a fundamental difference in the 3' UTR regulatory mechanisms controlling the temporal induction of maternal Mos mRNA polyadenylation and translational activation during Xenopus and mammalian oocyte maturation.

Spatial and temporal expression of c-mos in mouse testis during postnatal development.

AIM: To immunolocalize the c-mos gene product and to investigate its spatial and temporal expression in mouse testis during postnatal development. METHODS: Semi-quantitative reverse transcription-polymerase chain reaction (RT-PCR) and in situ hybridization techniques were used to examine c-mos mRNA and indirect immunofluorescence was used to localize c-Mos protein in mouse testis on postnatal days 14, 21, 25, 28, 30, 35, 49 and 70. RESULTS: c-mos mRNA remained low on postnatal days 14-21, increased abruptly from day 25 and peaked on day 30. Its levels decreased a little on day 35 and became almost stable thereafter until day 70. c-mos mRNA was localized in the nucleus and cytoplasm of the spermatocytes and round spermatids. The nuclear staining was much stronger than the cytoplasmic staining. Using a polyclonal anti-c-Mos antibody, Western blotting detected a single band at 43 kDa in testis lysate. c-Mos protein was exclusively localized to the elongating spermatids and was first detected on postnatal day 30. The number of c-Mos-positive spermatids increased progressively till day 49 and stabilized thereafter. CONCLUSION: The c-mos gene displays a spatial and temporal expression pattern in the mouse testis during postnatal development at both the mRNA and protein level. This suggests that c-mos might play important roles in spermatogenesis.

The Drosophila MOS ortholog is not essential for meiosis.

In metazoan oocytes, a metaphase arrest coordinates the completion of meiosis with fertilization. Vertebrate mos maintains the metaphase II arrest of mature oocytes and prevents DNA replication between the meiotic divisions. We identified a Drosophila homolog of mos and showed it to be the mos ortholog by two additional criteria. The dmos transcripts are present in Drosophila oocytes but not embryos, and injection of dmos into Xenopus embryos blocks mitosis and elevates active MAPK levels. In Drosophila, MAPK is activated in oocytes, consistent with a role in meiosis. We generated deletions of dmos and found that, as in vertebrates, dmos is responsible for the majority of MAPK activation. Unexpectedly, the oocytes that do mature complete meiosis normally and produce fertilized embryos that develop, although there is a reduction in female fertility and loss of some oocytes by apoptosis. Therefore, Drosophila contains a mos ortholog that activates a MAPK cascade during oogenesis and is nonessential for meiosis. This could be because there are redundant pathways regulating meiosis, because residual, low levels of active MAPK are sufficient, or because active MAPK is dispensable for meiosis in Drosophila. These results highlight the complexity of meiotic regulation that evolved to ensure accurate control over the reproductive process.