A new Arabidopsis nucleic-acid-binding protein gene is highly expressed in dividing cells during development

An Arabidopsis thaliana cDNA encoding a new RNA-binding protein (RBP37) was cloned from a silique cDNA library. The predicted amino acid sequence corresponds to a RBP containing two RNA recognition motifs (RRM) and a basic domain. An affinity for nucleic acids was confirmed in binding assays using in vitro synthesised AtRBP37 protein. In situ hybridisation experiments on sections of flowers and siliques showed expression only in growing organs: gynoecium, petals, filaments and during early-embryogenesis expression is located in the embryo proper and the suspensor up to late heart stage. Expression is not detected in the embryo during maturation.This results suggests an expression pattern correlated with dividing cells.     

Aint/Tacc3 is highly expressed in proliferating mouse tissues during development, spermatogenesis, and oogenesis.

Aint was originally identified on the basis of its interaction in vitro with the aryl hydrocarbon nuclear receptor translocator (Arnt). Arnt is a common heterodimerization partner in the basic helix-loop-helix (bHLH)-PER-ARNT-SIM (PAS) protein family and is involved in diverse biological functions. These include xenobiotic metabolism, hypoxic response, and circadian rhythm. In addition, Arnt has a crucial role during development. Aint is a member of a growing family of transforming acidic coiled-coil (TACC) proteins and is the murine homologue of human TACC3. Here we report the spatiotemporal expression of Tacc3 mRNA and protein in embryonic, postnatally developing, and adult mouse tissues using in situ hybridization and immunocytochemistry. Tacc3 mRNA was highly expressed in proliferating cells of several organs during murine development. However, the only adult tissues expressing high levels were testis and ovary. Immunocytochemistry revealed that Tacc3 is a nuclear protein. Our results suggest that Tacc3 has an important role in murine development, spermatogenesis, and oogenesis.     

Intermediate-conductance Ca2+-activated K+ channel is expressed in C2C12 myoblasts and is downregulated during myogenesis

We report here the expression in C₂C₁₂ myoblasts of the intermediate-conductance Ca²⁺-activated K⁺ (IK_Ca) channel. The IK_Ca current, recorded under perforated-patch configuration, had a transient time course when activated by ionomycin (0.5 µM; peak current density 26.2 ± 3.7 pA/pF; n = 10), but ionomycin (0.5 µM) + 5,6-dichloro-1-ethyl-1,3-dihydro-2H-benzimidazol-2-one (100 µM) evoked a stable outward current (28.4 ± 8.2 pA/pF; n = 11). The current was fully inhibited by charybdotoxin (200 nM), clotrimazole (2 µM), and 5-nitro-2-(3-phenylpropylamino)benzoic acid (300 µM), but not by tetraethylammonium (1 mM) or D-tubocurarine (300 µM). Congruent with the IK_Ca channel, elevation of intracellular Ca²⁺ in inside-out patches resulted in the activation of a voltage-insensitive K⁺ channel with weak inward rectification, a unitary conductance of 38 ± 6 pS (at negative voltages), and an IC₅₀ for Ca²⁺ of 530 nM. The IK_Ca channel was activated metabotropically by external application of ATP (100 µM), an intracellular Ca²⁺ mobilizer. Under current-clamp conditions, ATP application resulted in a membrane hyperpolarization of 35 mV. The IK_Ca current downregulated during myogenesis, ceasing to be detectable 4 days after the myoblasts were placed in differentiating medium. Downregulation was prevented by the myogenic suppressor agent basic FGF (bFGF). We also found that block of the IK_Ca channel by charybdotoxin did not inhibit bFGF-sustained myoblast proliferation. These observations show that in C₂C₁₂ myoblasts the IK_Ca channel expression correlates inversely with differentiation, yet it does not appear to have a role in myoblast proliferation. ATP; cell proliferation     

The LIM domain protein Lmo4 is highly expressed in proliferating mouse epithelial tissues.

LMO4 belongs to the LIM-only family of zinc finger proteins that have been implicated in oncogenesis. The LMO4 gene is overexpressed in breast cancer and oral cavity carcinomas, and high levels of this protein inhibit mammary epithelial differentiation. Targeted deletion of Lmo4 in mice leads to complex phenotypic abnormalities and perinatal lethality. To further understand the role of LMO4, we have characterized Lmo4 expression in adult mouse tissues by immunohistochemical staining using monoclonal anti-Lmo4 antibodies. Lmo4 was highly expressed within specific cell types in diverse tissues. Expression was prevalent in epithelial-derived tissues, including the mammary gland, tongue, skin, small intestine, lung, and brain. High levels of Lmo4 were frequently observed in proliferating cells, such as the crypt cells of the small intestine and the basal cells of the skin and tongue. Lmo4 was highly expressed in the proliferative cap cell layer of the terminal end buds in the peripubertal mammary gland and in the lobuloalveolar units during pregnancy. The expression profile of Lmo4 suggests that this cofactor is an important regulator of epithelial proliferation and has implications for its role in the pathogenicity of cancer.     

The tobacco extensin gene Ext 1.4 is expressed in cells submitted to mechanical restraints and in cells proliferating under hormone control

The promoter region of a Nicotiana tabacum extensin gene (Ext 1.4) was studied in tobacco transgenic plants carrying Ext 1.4/GUS (-glucuronidase) chimeric genes. The pattern of expression could be defined and cis-regulatory elements were localized in small regions of the promoter. In healthy plants, expression was essentially found in cells under mechanical stress, that is at the emergence of lateral roots, at the junction between stem and petiole and at the fusion of carpels. In roots of germinating plantlets, expression was found in the piliferous zone. In flowers, expression was found on the one hand in the placenta, in the locular tissue of ovaries and in the zone of carpel fusion, and on the other hand in the connective tissue of anthers, in mature and in germinating pollen. A developmental regulation during seed germination, where the gene fusion is transiently expressed in the endosperm and in the root tip before its expression becomes similar to that found in mature plants has also been shown. The expression of the Ext 1.4/GUS chimeric gene was also induced during cell proliferation under hormone control, for example in response to Agrobacterium tumefaciens infection and in calli. However, when organogenesis occurred under hormone control, expression was never found in root or shoot primordia. Cis-regulatory elements important for expression of the Ext 1.4 GUS gene fusion in germinating seeds, in mature plants or in proliferating cells have been localized in the proximal promoter region whereas enhancer elements have been located further upstream.     

ATAD2B is a phylogenetically conserved nuclear protein expressed during neuronal differentiation and tumorigenesis

ATAD2 is an E2F target gene that is highly expressed in gastrointestinal and breast carcinomas. Here we characterize a related gene product, ATAD2B. Both genes are evolutionarily conserved, with orthologues present in all eukaryotic genomes examined. Human ATAD2B shows a high degree of similarity to ATAD2. Both contain an AAA domain and a bromodomain with amino acid sequences sharing 97% and 74% identity, respectively. The expression of ATAD2B was studied in the chicken embryo using a polyclonal antibody raised against a recombinant fragment of human ATAD2B. Immunohistochemistry revealed transient nuclear expression in subpopulations of developing neurons. The transient nature of the expression was confirmed by immunoblotting homogenates of the developing telencephalon. Cell fractionation was used to confirm the nuclear localization of ATAD2B in the developing nervous system: anti-ATAD2B recognizes a smaller band (approximately 160 kDa) in the nuclear fraction and a larger band (approximately 300 kDa) in the membrane fraction, suggesting that posttranslational processing of ATAD2B may regulate its transport to the nucleus. The expression of ATAD2B was also studied in human tumors. Oncomine and immunohistochemistry reveal ATAD2B expression in glioblastoma and oligodendroglioma; ATAD2B immunostaining was also elevated in human breast carcinoma. In tumors ATAD2B appears to be cytoplasmic or membrane bound, and not nuclear. Our observations suggest that ATAD2B may play a role in neuronal differentiation and tumor progression.     

The Arabidopsis HINKEL gene encodes a kinesin-related protein involved in cytokinesis and is expressed in a cell cycle-dependent manner

Plant cytokinesis starts in the center of the division plane, with vesicle fusion generating a new membrane compartment, the cell plate, that subsequently expands laterally by continuous fusion of newly arriving vesicles to its margin. Targeted delivery of vesicles is assisted by the dynamic reorganization of a plant-specific cytoskeletal array, the phragmoplast, from a solid cylinder into an expanding ring-shaped structure. This lateral translocation is brought about by depolymerization of microtubules in the center, giving way to the expanding cell plate, and polymerization of microtubules along the edge. Whereas several components are known to mediate cytokinetic vesicle fusion [8-10], no gene function involved in phragmoplast dynamics has been identified by mutation. Mutations in the Arabidopsis HINKEL gene cause cytokinesis defects, such as enlarged cells with incomplete cell walls and multiple nuclei. Proper targeting of the cytokinesis-specific syntaxin KNOLLE [8] and lateral expansion of the phragmoplast are not affected. However, the phragmoplast microtubules appear to persist in the center, where vesicle fusion should result in cell plate formation. Molecular analysis reveals that the HINKEL gene encodes a plant-specific kinesin-related protein with a putative N-terminal motor domain and is expressed in a cell cycle-dependent manner similar to the KNOLLE gene. Our results suggest that HINKEL plays a role in the reorganization of phragmoplast microtubules during cell plate formation.     

Patt1, a novel protein acetyltransferase that is highly expressed in liver and downregulated in hepatocellular carcinoma,enhances apoptosis of hepatoma cells

Protein acetylation is increasingly recognized as an important post-translational modification. Although a lot of protein acetyltransferases have been identified, a few putative acetyltransferases are yet to be studied. In this study, we identified a novel protein acetyltransferase, Patt1, which belongs to GNAT family. Patt1 exhibited histone acetyltransferase activity and auto-acetylation activity. Deletion and mutation analysis of the predicted acetyltransferase domain in Patt1 showed that the conserved Glu139 was an important residue for its protein acetyltransferase activity. Furthermore, we found that Patt1 was highly expressed in liver and significantly downregulated in hepatocellular carcinoma tissues. In addition, we showed that overexpression of Patt1 enhanced the apoptosis of hepatoma cells dependent on its acetyltransferase activity, whereas knockdown of Patt1 significantly protected Chang liver cells from apoptosis. These data suggest that Patt1 might be involved in the development of hepatocellular carcinoma, and could be served as a potential therapy target for hepatocellular carcinoma.