Isolation of a novel cDNA that encodes a protein localized to the pre-acrosome region of spermatids

CEP131 knockdown inhibits cell proliferation by inhibiting the ERK and AKT signaling pathways in non-small cell lung cancer

Disrupted centrosome-associated family protein expression can result in the detrimental duplication of centrosomes, causing genomic instability and subsequent carcinogenesis. Limited research has demonstrated that centrosomal protein 131 (CEP131) exhibits oncogenic activity in osteosarcoma, hepatocellular carcinoma and breast cancer. The present study demonstrated that there is an association between CEP131 expression and advanced Tumor-Node-Metastasis stage (P=0.016), and positive regional lymph node metastasis (P=0.023) in 91 cases of non-small cell lung cancer. A549 and SPC-A-1 cells, with moderate expression levels of CEP131, were selected as representative cell lines. The results indicated that downregulation of CEP131 induced G1/S cell cycle arrest, inhibition of cyclins D1/E and cyclin-dependent kinases 2/4/6, and induction of inhibitory p21/p27, all of which are regulated by ERK and AKT signaling, suggesting that CEP131 exhibits potential as a novel target in the treatment of lung cancer.

RNA-mediated gene fusion in mammalian cells

One of the hallmarks of cancer is the formation of oncogenic fusion genes as a result of chromosomal translocations. Fusion genes are presumed to form before fusion RNA expression. However, studies have reported the presence of fusion RNAs in individuals who were negative for chromosomal translocations. These observations give rise to "the cart before the horse" hypothesis, in which the genesis of a fusion RNA precedes the fusion gene. The fusion RNA then guides the genomic rearrangements that ultimately result in a gene fusion. However, RNA-mediated genomic rearrangements in mammalian cells have never been demonstrated. Here we provide evidence that expression of a chimeric RNA drives formation of a specified gene fusion via genomic rearrangement in mammalian cells. The process is: (i) specified by the sequence of chimeric RNA involved, (ii) facilitated by physiological hormone levels, (iii) permissible regardless of intrachromosomal (TMPRSS2-ERG) or interchromosomal (TMPRSS2-ETV1) fusion, and (iv) can occur in normal cells before malignant transformation. We demonstrate that, contrary to "the cart before the horse" model, it is the antisense rather than sense chimeric RNAs that effectively drive gene fusion, and that this disparity can be explained by transcriptional conflict. Furthermore, we identified an endogenous RNA AZI1 that functions as the "initiator" RNA to induce TMPRSS2-ERG fusion. RNA-driven gene fusion demonstrated in this report provides important insight in early disease mechanisms, and could have fundamental implications in the biology of mammalian genome stability, as well as gene-editing technology via mechanisms native to mammalian cells.

Regulation of centriolar satellite integrity and its physiology

Centriolar satellites comprise cytoplasmic granules that are located around the centrosome. Their molecular identification was first reported more than a quarter of a century ago. These particles are not static in the cell but instead constantly move around the centrosome. Over the last decade, significant advances in their molecular compositions and biological functions have been achieved due to comprehensive proteomics and genomics, super-resolution microscopy analyses and elegant genetic manipulations. Centriolar satellites play pivotal roles in centrosome assembly and primary cilium formation through the delivery of centriolar/centrosomal components from the cytoplasm to the centrosome. Their importance is further underscored by the fact that mutations in genes encoding satellite components and regulators lead to various human disorders such as ciliopathies. Moreover, the most recent findings highlight dynamic structural remodelling in response to internal and external cues and unexpected positive feedback control that is exerted from the centrosome for centriolar satellite integrity.

Acute versus chronic loss of mammalian Azi1/Cep131 results in distinct ciliary phenotypes

Defects in cilium and centrosome function result in a spectrum of clinically-related disorders, known as ciliopathies. However, the complex molecular composition of these structures confounds functional dissection of what any individual gene product is doing under normal and disease conditions. As part of an siRNA screen for genes involved in mammalian ciliogenesis, we and others have identified the conserved centrosomal protein Azi1/Cep131 as required for cilia formation, supporting previous Danio rerio and Drosophila melanogaster mutant studies. Acute loss of Azi1 by knock-down in mouse fibroblasts leads to a robust reduction in ciliogenesis, which we rescue by expressing siRNA-resistant Azi1-GFP. Localisation studies show Azi1 localises to centriolar satellites, and traffics along microtubules becoming enriched around the basal body. Azi1 also localises to the transition zone, a structure important for regulating traffic into the ciliary compartment. To study the requirement of Azi1 during development and tissue homeostasis, Azi1 null mice were generated (Azi1^Gt/Gt). Surprisingly, Azi1^Gt/Gt MEFs have no discernible ciliary phenotype and moreover are resistant to Azi1 siRNA knock-down, demonstrating that a compensation mechanism exists to allow ciliogenesis to proceed despite the lack of Azi1. Cilia throughout Azi1 null mice are functionally normal, as embryonic patterning and adult homeostasis are grossly unaffected. However, in the highly specialised sperm flagella, the loss of Azi1 is not compensated, leading to striking microtubule-based trafficking defects in both the manchette and the flagella, resulting in male infertility. Our analysis of Azi1 knock-down (acute loss) versus gene deletion (chronic loss) suggests that Azi1 plays a conserved, but non-essential trafficking role in ciliogenesis. Importantly, our in vivo analysis reveals Azi1 mediates novel trafficking functions necessary for flagellogenesis. Our study highlights the importance of both acute removal of a protein, in addition to mouse knock-out studies, when functionally characterising candidates for human disease.

Cilia are slender projections from the surface of most mammalian cells and have sensory and sometimes motile functions. They are essential for mammalian development and defects in cilia lead to a group of human diseases, termed ciliopathies, with variable symptoms including embryonic lethality, lung and kidney defects, blindness and infertility. Cilia are complex structures composed of hundreds of components, whose individual functions are poorly understood. We screened for mammalian genes important in building cilia, and identified Azi1/Cep131, a gene previously shown to be required for cilia formation and function in fish and flies. We show that if we acutely reduce levels of Azi1 in mouse cells, fewer cells form cilia, but if we generate cells chronically lacking all Azi1, cilia form normally. In addition, mice without any Azi1 are healthy and viable, confirming normal cilia function. However, in these mice, the highly specialised ciliary structure of the sperm tail does not form, resulting in male infertility. We suggest Azi1 has conserved trafficking roles in both primary cilia and the specialised sperm flagella. Abruptly removing Azi1 results in instability causing the existing cilia network to collapse, whereas chronic deletion of Azi1 allows the system to re-equilibrate, and cilia to form normally.

The centriolar satellite protein Cep131 is important for genome stability

The centrosome acts as a centre for microtubule organisation and plays crucial roles in cell polarity, migration, growth and division. Cep131 has recently been described as a basal body component essential for cilium formation, but its function in non-ciliogenic cells is unknown. We identified human Cep131 (also known as AZI1) in a screen for regulators of genome stability. We show that centrosomal localisation of Cep131 is cell-cycle-regulated and requires both an intact microtubule network and a functional dynein-dynactin transport system. Cep131 is recruited to centriolar satellites by PCM1, and localised to the centriolar core region by both pericentrin and Cep290. Depletion of Cep131 results in a reduction in proliferation rate, centriole amplification, an increased frequency of multipolar mitosis, chromosomal instability and an increase in post-mitotic DNA damage. These data therefore highlight the importance of human Cep131 for maintaining genomic integrity.

Dilatory is a Drosophila protein related to AZI1 (CEP131) that is located at the ciliary base and required for cilium formation

A significant number of ciliary disease genes have been found to encode proteins that localise to the basal body. By contrast, a large number of basal-body-associated proteins remain to be characterised. Here, we report the identification of a new basal body protein that is required for ciliogenesis in Drosophila. Dilatory (DILA) is a predicted coiled-coil protein homologous to vertebrate AZI1 (also known as CEP131). Mutations in dila specifically exhibit defects in ciliated cells (sensory neurons and sperm). Several features of the neuronal phenotype suggest a defect in intraflagellar transport. In sensory neuron cilia, DILA protein localises to the ciliary base, including the basal body and putative transition zone, and it interacts genetically with the ciliary coiled-coil protein, Uncoordinated. These data implicate DILA in regulating intraflagellar transport at the base of sensory cilia.

The protein encoded by cancer/testis gene D40/AF15q14 is localized in spermatocytes, acrosomes of spermatids and ejaculated spermatozoa

We have previously identified and cloned a human gene, D40, that is preferentially expressed in testis among normal organs, while it is widely expressed in various human tumor cell lines and primary tumors derived from different organs. In this report, we have examined the expression and localization of this protein in human testis with an antibody specific to D40 protein. In Western analyses, the anti-D40 antibody recognized a major band with a molecular mass of 300 kDa and a minor band of 250 kDa. These bands were not observed in the testis lysates from patients with Sertoli-cell-only syndrome and with Kleinfelter syndrome, who lack germ cells of the testis, indicating that D40 protein is expressed in the germ cells of normal testis. Immunohistochemical studies have revealed that D40 protein is highly expressed in spermatocytes and in the pre-acrosome of round spermatids. In the acrosome, D40 protein expression is observed not inside but outside the acrosome membrane. This is consistent with the finding that the amino-acid sequence at the amino terminal of the D40 protein lacks a hydrophobic signal peptide that is required for proteins to translocate to the membrane. Expression of D40 protein is observed in the acrosome of ejaculated spermatozoa as well, although the level is low compared with that in the pre-acrosome of spermatids. These results suggest that D40 protein plays important roles in spermatogenesis, especially in the formation and maintenance of the acrosome.

Increased cell proliferation and R.Msp1 fragmentation induced by 5-aza-2'-deoxycytidine in rat testes related to the gene imprinting mechanism

DNA methylation is one of the crucial mechanisms for cellular and tissue differentiation during developmental stages in mammals. 5-aza-2'-deoxycytidine, a specific cytosine DNA Methyltransferase inhibitor, is known to cause DNA hypomethylation in CpG, CpNpG and CCGG sequences. Therefore the present study was designed to determine the effects of 5-aza-2'-deoxycytidine on the germinal cells of the adult rat testicular tissue. Rat testicular tissues from the 5-aza-2'-deoxycytidine treated experimental and non-treated control groups were processed for light microscopy and also for genomic DNA isolation assays. The isolated genomic DNAs were digested with R.Msp1 in order to determine the methyl pattern differences in the enzyme cognate CCGG sequence. Testicular tissues from treated rats showed increased cell proliferation when investigated at the light microscopical level. On the other hand, genomic DNA of these proliferative tissue showed high fragmentation sizes of R.Msp1 digestion when compared to controls. While the R.Msp1 digested control group DNA fragmentation condensed at approximately 4700-5100 bps size, the experimental group DNA fragmentation was condensed at 700-900 bps size. In addition, 5-aza-2'-deoxycytidine has effects on increased cell proliferation via the loss of somatic de novo gene imprinting. These results imply that abnormally imprinted normal somatic cells in mammals are susceptible to epigenetic modification. These results also suggest that the genomic DNA of testicular tissues from control rats is resistant to R.Msp1 while DNA from the experimental group testicular cells demonstrating high proliferation rate could not resist to R.Msp1 digestion due to DNA hypomethylation in CCGG sequence. In conclusion, it could be suggested that the reversal of gene imprinting in germinal cells may cause an increased cellular proliferation and R.Msp1 fragmentation when induced by 5-aza-2'-deoxycytidine.

Isolation of the novel cDNA of a gene of which expression is induced by a demethylating stimulus

We have isolated a novel cDNA clone, named AZ2, from a cDNA library of mRNA prepared from C3H10T1/2 cells that had been transiently exposed to 5-azacytidine, a potent inhibitor of DNA methyltransferase. The elucidated nucleotide sequence revealed that the 5' region of the cDNA was rich in the CpG sequence. The AZ2 cDNA contained a 1215-nucleotide open reading frame, and the expected amino acid sequence had a molecular mass of 46090. The amount of the transcript increased on 5-azacytidine treatment of C3H10T1/2 cells, and the transcript was significantly expressed in mouse testis, brain, lung, kidney, heart and ovary. Specific antibodies raised against a fusion protein including glutathione S-transferase revealed a band of an approximately 48kDa translation product for testis, brain, lung, and cultured cells that ectopically expressed the AZ2 protein. The AZ2 protein was mainly localized in the cytoplasm. The amino-terminal part of the AZ2 protein was homologous to the previously reported TANK (Cheng and Baltimore, 1996. Genes Dev. 10, 963-973) and I-TRAF (Rothe, 1996. Proc. Natl. Acad. Sci. USA 93, 8241-8246), which participate in the signal transduction cascade from the tumor necrosis factor-receptor to the transcription factor, NFkappaB. Overexpression of AZ2 inhibited TNF alpha mediated NFkappaB activation. AZ2 could be a component of a regulator of the NFkappaB activation cascade.

Carrot DNA-methyltransferase is encoded by two classes of genes with differing patterns of expression

In the present study, the isolation and characterization of two distinct cDNAs that code for carrot DNA (cytosine-5)-methyltransferase (DNA-METase) are reported. The screening of a cDNA library with a carrot genomic DNA fragment, previously obtained by PCR using degenerate primers, has led to the isolation of clones that belong to two distinct classes of genes (Met1 and Met2) which differ in sequence and size. Met1-5 and Met2-21 derived amino acid sequences are more than 85% identical for most of the polypeptide and completely diverge at the N-terminus. The larger size of the Met2-21 cDNA is due to the presence of nearly perfect fivefold repeat of a 171 bp sequence present only once in the Met1-5 cDNA. Northern and in situ hybridization analyses with young carrot plants and somatic embryos indicate that both genes are maximally expressed in proliferating cells (suspension cells, meristems and leaf primordia), but differ quantitatively and spatially in their mode of expression. Polyclonal antibodies were raised in rabbit using fusion proteins corresponding to the regulatory and catalytic regions of the most highly expressed gene (Met1-5). In nuclear carrot extracts, both antibodies were found to recognize a band of about 200 kDa along with some additional bands of lower size. These results provide the first direct demonstration that DNA-METases of a higher eukaryote are encoded by a gene family.

Genomic organization of the mouse AZ1 gene that encodes the protein localized to preacrosomes of spermatids

The AZ1 protein is localized to the preacrosome region of spermatids. Previous developmental studies suggested that AZ1 gene transcription begins in pachytene spermatocytes and that expression of the gene is induced in cultivated fibroblasts on treatment with 5-azacytidine, which is known to lead to the demethylation of genomic DNA. In the present study, we cloned the gene coding AZ1 cDNA and elucidated its genomic organization. AZ1 cDNA was encoded by 25 exons distributed within 25 kb of genomic DNA. The transcription started at nucleotide positions -312 and -311 of the cDNA, with the A of the ATG codon specifying the initiator methionine assigned as nucleotide position +1. Exon 1 and a part of intron 1 of the AZ1 gene constituted a typical CpG island, and an about 0.2-kb sequence of the 5'-proximal region exhibited a G + C content and CpG ratio higher than the averages for the mammalian genomic sequence.

Spermatocyte-specific expression of the gene for mouse testis-specific transcription elongation factor S-II

Previously, we characterized a rat cDNA for testis-specific transcription elongation factor S-II (SII-T1) (Q. Xu et al., J. Biol. Chem. 269, 3100-3103 (1994)). Here, we isolated a 335-bp fragment of the cDNA for mouse SII-T1, and used it to examine the expression of the SII-T1 gene in the testis by in situ hybridization. The results indicated that the SII-T1 gene is expressed exclusively in spermatocytes, showing no appreciable expression in spermatogonia, spermatids, or Leydig cells. RT-PCR experiments using testis RNA from W/Wv mutant mice also suggested that SII-T1 is a specific transcription elongation factor essential for spermatogenesis.