Current Insights into Research on Rice stripe virus

Rice stripe virus (RSV) is one of the most destructive viruses of rice, and greatly reduces rice production in China, Japan, and Korea, where mostly japonica cultivars of rice are grown. RSV is transmitted by the small brown plant-hopper (SBPH) in a persistent and circulative-propagative manner. Several methods have been developed for detection of RSV, which is composed of four single-stranded RNAs that encode seven proteins. Genome sequence data and comparative phylogenetic analysis have been used to identify the origin and diversity of RSV isolates. Several rice varieties resistant to RSV have been selected and QTL analysis and fine mapping have been intensively performed to map RSV resistance loci or genes. RSV genes have been used to generate several genetically modified transgenic rice plants with RSV resistance. Recently, genome-wide transcriptome analyses and deep sequencing have been used to identify mRNAs and small RNAs involved in RSV infection; several rice host factors that interact with RSV proteins have also been identified. In this article, we review the current statues of RSV research and propose integrated approaches for the study of interactions among RSV, rice, and the SBPH.

Insight into mycoviruses infecting Fusarium species

Most of the major fungal families including plant-pathogenic fungi, yeasts, and mushrooms are infected by mycoviruses, and many double-stranded RNA (dsRNA) mycoviruses have been recently identified from diverse plant-pathogenic Fusarium species. The frequency of occurrence of dsRNAs is high in Fusarium poae but low in other Fusarium species. Most Fusarium mycoviruses do not cause any morphological changes in the host but some mycoviruses like Fusarium graminearum virus 1 (FgV1) cause hypovirulence. Available genomic data for seven of the dsRNA mycoviruses infecting Fusarium species indicate that these mycoviruses exist as complexes of one to five dsRNAs. According to phylogenetic analysis, the Fusarium mycoviruses identified to date belong to four families: Chrysoviridae, Hypoviridae, Partitiviridae, and Totiviridae. Proteome and transcriptome analysis have revealed that FgV1 infection of Fusarium causes changes in host transcriptional and translational machineries. Successful transmission of FgV1 via protoplast fusion suggests the possibility that, as biological control agents, mycoviruses could be introduced into diverse species of fungal plant pathogens. Research is now needed on the molecular biology of mycovirus life cycles and mycovirus-host interactions. This research will be facilitated by the further development of omics technologies.

Loop-mediated isothermal amplification for the rapid detection of Chrysanthemum chlorotic mottle viroid (CChMVd)

Loop-mediated isothermal amplification (LAMP) is an established nucleic acid amplification method offering rapid, sensitive, and convenient diagnosis of infectious diseases. Chrysanthemum chlorotic mottle viroid (CChMVd) causes one of the most serious viral diseases in chrysanthemum in Korea. A sensitive LAMP assay was developed for rapidly detecting CChMVd infection. The assay was based on a set of four primers matching the specific region of the CChMVd genome. The CChMVd LAMP primer sets were designed using the sequences from nonsymptomatic and symptomatic CChMVd isolates in Korea. The efficiency and specificity of this method were optimized using Bst DNA polymerase, which allowed for increased viroid detection sensitivity. The reaction was carried out at 65 °C for 90 min, and was improved by adding SYBR Green I dye to the inside of the reaction tube lid prior to amplification. The results indicate that this LAMP method will be useful for chrysanthemum viroid disease monitoring and detecting CChMVd infectious disease.

Phylogenetic and recombination analysis of tomato spotted wilt virus

Tomato spotted wilt virus (TSWV) severely damages and reduces the yield of many economically important plants worldwide. In this study, we determined the whole-genome sequences of 10 TSWV isolates recently identified from various regions and hosts in Korea. Phylogenetic analysis of these 10 isolates as well as the three previously sequenced isolates indicated that the 13 Korean TSWV isolates could be divided into two groups reflecting either two different origins or divergences of Korean TSWV isolates. In addition, the complete nucleotide sequences for the 13 Korean TSWV isolates along with previously sequenced TSWV RNA segments from Korea and other countries were subjected to phylogenetic and recombination analysis. The phylogenetic analysis indicated that both the RNA L and RNA M segments of most Korean isolates might have originated in Western Europe and North America but that the RNA S segments for all Korean isolates might have originated in China and Japan. Recombination analysis identified a total of 12 recombination events among all isolates and segments and five recombination events among the 13 Korea isolates; among the five recombinants from Korea, three contained the whole RNA L segment, suggesting reassortment rather than recombination. Our analyses provide evidence that both recombination and reassortment have contributed to the molecular diversity of TSWV.

Evolution of and horizontal gene transfer in the Endornavirus genus

The transfer of genetic information between unrelated species is referred to as horizontal gene transfer. Previous studies have demonstrated that both retroviral and non-retroviral sequences have been integrated into eukaryotic genomes. Recently, we identified many non-retroviral sequences in plant genomes. In this study, we investigated the evolutionary origin and gene transfer of domains present in endornaviruses which are double-stranded RNA viruses. Using the available sequences for endornaviruses, we found that Bell pepper endornavirus-like sequences homologous to the glycosyltransferase 28 domain are present in plants, fungi, and bacteria. The phylogenetic analysis revealed the glycosyltransferase 28 domain of Bell pepper endornavirus may have originated from bacteria. In addition, two domains of Oryza sativa endornavirus, a glycosyltransferase sugar-binding domain and a capsular polysaccharide synthesis protein, also exhibited high similarity to those of bacteria. We found evidence that at least four independent horizontal gene transfer events for the glycosyltransferase 28 domain have occurred among plants, fungi, and bacteria. The glycosyltransferase sugar-binding domains of two proteobacteria may have been horizontally transferred to the genome of Thalassiosira pseudonana. Our study is the first to show that three glycome-related viral genes in the genus Endornavirus have been acquired from marine bacteria by horizontal gene transfer.

A current overview of two viroids that infect chrysanthemums: Chrysanthemum stunt viroid and Chrysanthemum chlorotic mottle viroid

The chrysanthemum (Dendranthema X grandiflorum) belongs to the family Asteraceae and it is one of the most popular flowers in the world. Viroids are the smallest known plant pathogens. They consist of a circular, single-stranded RNA, which does not encode a protein. Chrysanthemums are a common host for two different viroids, the Chrysanthemum stunt viroid (CSVd) and the Chrysanthemum chlorotic mottle viroid (CChMVd). These viroids are quite different from each other in structure and function. Here, we reviewed research associated with CSVd and CChMVd that covered disease symptoms, identification, host range, nucleotide sequences, phylogenetic relationships, structures, replication mechanisms, symptom determinants, detection methods, viroid elimination, and development of viroid resistant chrysanthemums, among other studies. We propose that the chrysanthemum and these two viroids represent convenient genetic resources for host-viroid interaction studies.

Highly Specific Detection of Five Exotic Quarantine Plant Viruses using RT-PCR

To detect five plant viruses (Beet black scorch virus, Beet necrotic yellow vein virus, Eggplant mottled dwarf virus, Pelargonium zonate spot virus, and Rice yellow mottle virus) for quarantine purposes, we designed 15 RT-PCR primer sets. Primer design was based on the nucleotide sequence of the coat protein gene, which is highly conserved within species. All but one primer set successfully amplified the targets, and gradient PCRs indicated that the optimal temperature for the 14 useful primer sets was 51.9°C. Some primer sets worked well regardless of annealing temperature while others required a very specific annealing temperature. A primer specificity test using plant total RNAs and cDNAs of other plant virus-infected samples demonstrated that the designed primer sets were highly specific and generated reproducible results. The newly developed RT-PCR primer sets would be useful for quarantine inspections aimed at preventing the entry of exotic plant viruses into Korea.

Cis-acting element (SL1) of Potato virus X controls viral movement by interacting with the NbMPB2Cb and viral proteins

A number of candidate tobacco proteins that bind to cis-acting elements (SL1 RNAs) of Potato virus X (PVX) have been identified in previous studies. We further characterized TMV-MP30 binding protein 2C (MPB2C) homologous protein. We isolated NbMPB2Cb from Nicotiana benthamiana and confirmed the interaction of NbMPB2Cb with SL1 RNAs in vitro. The mRNA level of NbMPB2Cb was increased upon infection by PVX and Tobacco mosaic virus. The movement of PVX was reduced by overexpression of NbMPB2Cb and increased by silenced of NbMPB2Cb. In contrast, PVX RNA accumulation was not significantly altered in protoplasts. Protein-protein interaction assays showed that NbMPB2Cb interacts with PVX movement-associated proteins. PVX infection altered the subcellular localization of NbMPB2Cb from microtubules to endoplasmic reticulum. These data suggest that the NbMPB2Cb negatively affects PVX movement by interacting with SL1 RNAs and movement-associated proteins of PVX and by re-localizing in response to PVX infection.

Genome-wide expression profiling shows transcriptional reprogramming in Fusarium graminearum by Fusarium graminearum virus 1-DK21 infection

BACKGROUND

Fusarium graminearum virus 1 strain-DK21 (FgV1-DK21) is a mycovirus that confers hypovirulence to F. graminearum, which is the primary phytopathogenic fungus that causes Fusarium head blight (FHB) disease in many cereals. Understanding the interaction between mycoviruses and plant pathogenic fungi is necessary for preventing damage caused by F. graminearum. Therefore, we investigated important cellular regulatory processes in a host containing FgV1-DK21 as compared to an uninfected parent using a transcriptional approach.

RESULTS

Using a 3'-tiling microarray covering all known F. graminearum genes, we carried out genome-wide expression analyses of F. graminearum at two different time points. At the early point of growth of an infected strain as compared to an uninfected strain, genes associated with protein synthesis, including ribosome assembly, nucleolus, and ribosomal RNA processing, were significantly up-regulated. In addition, genes required for transcription and signal transduction, including fungal-specific transcription factors and cAMP signaling, respectively, were actively up-regulated. In contrast, genes involved in various metabolic pathways, particularly in producing carboxylic acids, aromatic amino acids, nitrogen compounds, and polyamines, showed dramatic down-regulation at the early time point. Moreover, genes associated with transport systems localizing to transmembranes were down-regulated at both time points.

CONCLUSION

This is the first report of global change in the prominent cellular pathways in the Fusarium host containing FgV1-DK21. The significant increase in transcripts for transcription and translation machinery in fungal host cells seems to be related to virus replication. In addition, significant down-regulation of genes required for metabolism and transporting systems in a fungal host containing the virus appears to be related to the host defense mechanism and fungal virulence. Taken together, our data aid in the understanding of how FgV1-DK21 regulates the transcriptional reprogramming of F. graminearum.

Identification of tobacco proteins associated with the stem-loop 1 RNAs of Potato virus X

Potato virus X (PVX) contains five viral proteins as well as cis-acting elements like stem-loop 1 (SL1) RNAs at the 5' region. SL1 RNAs are involved in PVX RNA replication, encapsidation, translation, and cell-to-cell movement. In this study, we performed two-dimensional electrophoresis Northwestern blot analysis and matrix-assisted laser desorption ionization time of flight mass spectrometry and identified 24 tobacco proteins that interact with SL1 RNAs. Interestingly, one-third of the identified host proteins have been shown to interact with many plant viral proteins. In addition, we demonstrated that PVX capsid protein can bind to both SL1(+/-) RNAs. We further selected three Nicotiana benthamiana proteins including NbMPB2Cb, NbMBF1, and NbCPIP2a, to confirm results of Northwestern blot analysis. Electrophoretic mobility shift assay showed that NbMPB2Cb and NbMBF1 bind to both SL1(+/-) RNAs in vitro. In contrast, NbCPIP2a interacts only SL1(+) RNA. Taken together, we provide a list of host proteins interacting with PVX SL1 RNAs, which would be good candidates for the study of viral RNA-host protein interaction.

The p19 protein of Grapevine Algerian latent virus is a determinant of systemic infection of Chenopodium quinoa

A previous study showed that both Grapevine Algerian latent virus (GALV) and Tomato bushy stunt virus (TBSV) systemically infect Nicotiana benthamiana, but GALV causes systemic infection whereas TBSV causes only local lesions in Chenopodium quinoa (C. quinoa). We recently isolated GALV strain Naju (GALV-N) from Limonium sinense and TBSV strain Sacheon (TBSV-S) from tomato. Both viruses belong to the genus Tombusvirus and have a similar genome organization. To identify determinants of systemic infection of GALV-N in C. quinoa in the current study, we generated infectious clones and capsid protein (CP)-deletion clones for the two viruses and confirmed that CP of GALV-N is required for systemic infection of C. quinoa due to its primary structural role in virus assembly. Through the use of chimeras, we identified a viral factor in addition to CP that contributes to systemic infection by GALV-N. Inactivation of the p19 demonstrated that host-specific activities of p19 are necessary for efficient systemic infection of C. quinoa by GALV-N. Our study is the first report to determine the viral factors required for systemic infection of GALV in C. quinoa.

Interaction of the host protein NbDnaJ with Potato virus X minus-strand stem-loop 1 RNA and capsid protein affects viral replication and movement

Plant viruses must interact with host cellular components to replicate and move from cell to cell. In the case of Potato virus X (PVX), it carries stem-loop 1 (SL1) RNA essential for viral replication and movement. Using two-dimensional electrophoresis northwestern blot analysis, we previously identified several host proteins that bind to SL1 RNA. Of those, we further characterized a DnaJ-like protein from Nicotiana benthamiana named NbDnaJ. An electrophoretic mobility shift assay confirmed that NbDnaJ binds only to SL1 minus-strand RNA, and bimolecular fluorescence complementation (BiFC) indicated that NbDnaJ interacts with PVX capsid protein (CP). Using a series of deletion mutants, the C-terminal region of NbDnaJ was found to be essential for the interaction with PVX CP. The expression of NbDnaJ significantly changed upon infection with different plant viruses such as PVX, Tobacco mosaic virus, and Cucumber mosaic virus, but varied depending on the viral species. In transient experiments, both PVX replication and movement were inhibited in plants that over-expressed NbDnaJ but accelerated in plants in which NbDnaJ was silenced. In summary, we suggest that the newly identified NbDnaJ plays a role in PVX replication and movement by interacting with SL1(-) RNA and PVX CP.

Genetic diversity of cultivable plant growth-promoting rhizobacteria in Korea

To elucidate the biodiversity of plant growth-promoting rhizobacteria (PGPR) in Korea, 7,638 bacteria isolated from the rhizosphere of plant species growing in many different regions were screened. A large number of PGPR were identified by testing the ability of each isolate to promote the growth of cucumber seedlings. After redundant rhizobacteria were removed via amplified rDNA restriction analysis, 90 strains were finally selected as PGPR. On the basis of 16S ribosomal RNA sequences, 68 Gram-positive (76%) and 22 Gram-negative (24%) isolates were assigned to 21 genera and 47 species. Of these genera, Bacillus (32 species) made up the largest complement, followed by Paenibacillus (19) and Pseudomonas (11). Phylogenetic analysis showed that most of the Grampositive PGPR fell into two categories: low- and high- G+C (Actinobacteria) strains. The Gram-negative PGPR were distributed in three categories: alpha-proteobacteria, beta- proteobacteria, and gamma-proteobacteria. To our knowledge, this is the largest screening study designed to isolate diverse PGPR. The enlarged understanding of PGPR genetic diversity provided herein will expand the knowledge base regarding beneficial plant-microbe interactions. The outcome of this research may have a practical effect on crop production methodologies.

Analysis of Arabidopsis transcription factor families revealed extensive capacity for cell-to-cell movement as well as discrete trafficking patterns

In plants, cell-to-cell communication is pivotal for the orchestration of cell fate determination, organ development, and the integration of whole plant physiology. One of the strategies for intercellular communication uses symplasmic communication channels, called plasmodesmata (PD). These PD establish unique cytoplasmic channels for the intercellular exchange not only of metabolites and small signaling molecules, but also of regulatory proteins and RNAs to allow for local orchestration of development and physiology. A number of non-cell-autonomous transcription factors (NCATFs) have been shown to function in the coordination of specific regulatory networks. To further explore the potential of such NCATFs, a genome-wide screen was performed on the transcription factor (TF) families in Arabidopsis. We here report that, among the 76 TFs examined, 22 were shown to move beyond their sites of transcription in the root apex; these NCATFs belonged to 17 TF families, including homeobox, GRAS, and MYB. Expression studies performed on variously-sized mCherry constructs identified a range of PD size exclusion limits within tissues of the root. In addition, our studies showed that actual protein level was an important factor controlling the range of TF intercellular movement. Interestingly, our studies on CAPRICE movement revealed tissue-specificity with respect to the mode of intercellular trafficking. These findings are discussed with respect to the regulation between cell-autonomous or non-cell-autonomous action.

Analysis of Arabidopsis transcription factor families revealed extensive capacity for cell-to-cell movement as well as discrete trafficking patterns

In plants, cell-to-cell communication is pivotal for the orchestration of cell fate determination, organ development, and the integration of whole plant physiology. One of the strategies for intercellular communication uses symplasmic communication channels, called plasmodesmata (PD). These PD establish unique cytoplasmic channels for the intercellular exchange not only of metabolites and small signaling molecules, but also of regulatory proteins and RNAs to allow for local orchestration of development and physiology. A number of non-cell-autonomous transcription factors (NCATFs) have been shown to function in the coordination of specific regulatory networks. To further explore the potential of such NCATFs, a genome-wide screen was performed on the transcription factor (TF) families in Arabidopsis. We here report that, among the 76 TFs examined, 22 were shown to move beyond their sites of transcription in the root apex; these NCATFs belonged to 17 TF families, including homeobox, GRAS, and MYB. Expression studies performed on variously-sized mCherry constructs identified a range of PD size exclusion limits within tissues of the root. In addition, our studies showed that actual protein level was an important factor controlling the range of TF intercellular movement. Interestingly, our studies on CAPRICE movement revealed tissue-specificity with respect to the mode of intercellular trafficking. These findings are discussed with respect to the regulation between cell-autonomous or non-cell-autonomous action.

How to assess the intercellular trafficking of transcription factors

Non-cell-autonomous (NCA) control of plant development is an emerging field. Transcription factors (TFs) are the most important plant proteins involved in development and cell fate determination. In plants specialized intercellular symplastic channels, called plasmodesmata (PD), facilitate and regulate the NCA action of TFs. NCA-TFs move from cell to cell either selectively or non-selectively depending upon the specific interactions with PD or the pathway proteins. Here we describe different approaches to establish the role of TFs in NCA control of its function and the characteristic movement behavior.

Plasmodesmal receptor-like kinases identified through analysis of rice cell wall extracted proteins

In plants, plasmodesmata (PD) are intercellular channels that function in both metabolite exchange and the transport of proteins and RNAs. Currently, many of the PD structural and regulatory components remain to be elucidated. Receptor-like kinases (RLKs) belonging to a notably expanded protein family in plants compared to the animal kingdom have been shown to play important roles in plant growth, development, pathogen resistance, and cell death. In this study, cell biological approaches were used to identify potential PD-associated RLK proteins among proteins contained within cell walls isolated from rice callus cultured cells. A total of 15 rice RLKs were investigated to determine their subcellular localization, using an Agrobacterium-mediated transient expression system. Of these six PD-associated RLKs were identified based on their co-localization with a viral movement protein that served as a PD marker, plasmolysis experiments, and subcellular localization at points of wall contact between spongy mesophyll cells. These findings suggest potential PD functions in apoplasmic signaling in response to environmental stimuli and developmental inputs.

Proteome study of the phloem sap of pumpkin using multidimensional protein identification technology

The phloem is the major transport route for both small substances and large molecules, such as proteins and RNAs, from their sources to sink tissues. To investigate the proteins present in pumpkin phloem sap, proteome analysis using multidimensional protein identification technology was carried out. Pumpkin phloem peptides obtained by liquid chromatography/mass spectrometry/mass spectrometry were searched against pumpkin protein data derived from the National Center for Biotechnology Information. A total of 47 pumpkin phloem proteins were identified. The identified proteins mainly corresponded to enzymes involved in gibberellin biosynthesis, antioxidation processes, or defense mechanisms. Interestingly, seven enzymes required for gibberellin biosynthesis were identified for the first time by this proteomics approach. In summary, the new phloem proteins identified in this study provide strong evidence for stress and defense signaling and new insights regarding the role of gibberellin in the developmental programming of higher plants through the phloem.

Proteomics of weakly bound cell wall proteins in rice calli

In the present work, we present a proteomic analysis of weakly bound cell wall proteins (CWPs) in rice. CWPs from rice calli were extracted with mannitol/CaCl(2), followed by back extraction with water-saturated phenol. The isolated CWPs were evaluated for contamination by cytosolic proteins by measuring the enzymatic activity of an intracellular marker (glucose-6-phosphate dehydrogenase). This revealed the presence of low levels of intracellular proteins and a significant enrichment of CWPs, as compared to the total extract. Protein samples were digested in gels with trypsin and analyzed using the multidimensional protein identification technology (MudPIT). A total of 292 proteins were identified, which included numerous classical CWPs and antioxidant proteins. Bioinformatics analysis showed that 72.6% of these proteins possessed a signal peptide, and a total of 198 proteins were determined to be CWPs in rice. Functional classification divided the extracellular proteins into different groups, including glycosyl hydrolases (23%), antioxidant proteins (12%), cell wall structure-related proteins (6%), metabolic pathways (9%), protein modifications (4%), defense (4%), and protease inhibitors (3%). Furthermore, comparative analysis of our identified rice CWPs with known Arabidopsis CWPs revealed 25 novel rice-specific CWPs. The study described here is an unprecedented large-scale analysis of CWPs in rice.

Proteomic analysis of the secretome of rice calli

The cell wall and extracellular matrix in higher plants include secreted proteins that play critical roles in a wide range of cellular processes, such as structural integrity and biogenesis. Compared with the intensive cell wall proteomic studies in Arabidopsis, the list of cell wall proteins identified in monocot species is lacking. Therefore, we conducted a large-scale proteomic analysis of secreted proteins from rice. Highly purified secreted rice proteins were obtained from the medium of a suspension of callus culture and were analyzed with multidimensional protein identification technology (MudPIT). As a result, we could detect a total of 555 rice proteins by MudPIT analysis. Based on bioinformatic analyses, 27.7% (154 proteins) of the identified proteins are considered to be secreted proteins because they possess a signal peptide for the secretory pathway. Among the 154 identified proteins, 27% were functionally categorized as stress response proteins, followed by metabolic proteins (26%) and factors involved in protein modification (24%). Comparative analysis of cell wall proteins from Arabidopsis and rice revealed that one third of the secreted rice proteins overlapped with those of Arabidopsis. Furthermore, 25 novel rice-specific secreted proteins were found. This work presents the large scale of the rice secretory proteome from culture medium, which contributes to a deeper understanding of the rice secretome.

Integrated analyses of the rice secretome

The plant cell wall contains proteins secreted from the cell. A subset of these proteins is called the secretome, which plays important roles in biological and physiological processes. To gain insight into the secretome for monocot species, we performed proteomic analysis of the rice secretome. In this addendum, we combined the results of two independent studies. For this, 154 rice secreted proteins from our study were compared to 42 non-redundant rice secreted proteins from another group. Surprisingly, only 20 proteins were commonly found in the two groups, indicating that the materials and methods are very important factors finding secreted proteins. Finally, a total of 172 rice secreted proteins were assigned molecular functions and biological processes according to gene ontology annotation. These comparative and integrative analyses of the rice secretome provide a large number of rice secreted proteins that can be used in subsequent investigations.

Characterization of soldat8, a suppressor of singlet oxygen-induced cell death in Arabidopsis seedlings

The flu mutant of Arabidopsis thaliana overaccumulates in the dark the immediate precursor of chlorophyllide, protochlorophyllide (Pchlide), a potent photosensitizer, that upon illumination generates singlet oxygen ((1)O2). Once (1)O2 has been released in plastids of the flu mutant, mature plants stop growing, while seedlings die. Several suppressor mutations, dubbed singlet oxygen-linked death activator (soldat), were identified that specifically abrogate (1)O2-mediated stress responses in young flu seedlings without grossly affecting (1)O2-mediated stress responses of mature flu plants. One of the soldat mutations, soldat8, was shown to impair a gene encoding the SIGMA6 factor of the plastid RNA polymerase. Reintroduction of a wild-type copy of the SOLDAT8 gene into the soldat8/flu mutant restored the phenotype of the flu parental line. In contrast to flu, seedlings of soldat8/flu did not bleach when grown under non-permissive dark/light conditions, despite their continuous overaccumulation of the photosensitizer Pchlide in the dark. The activity of SIGMA6 is confined primarily to the very early stage of seedling development. Inactivation of SIGMA6 in soldat8 mutants disturbed plastid homeostasis, drastically reduced the non-photochemical quenching capacity and enhanced the light sensitivity of young soldat8 seedlings. Surprisingly, after being grown under very low light, soldat8 seedlings showed an enhanced resistance against a subsequent severe light stress that was significantly higher than in wild-type seedlings. In order to reach a similar enhanced stress resistance, wild-type seedlings had to be exposed to a brief higher light treatment that triggered an acclimatory response. Such a mild pre-stress treatment did not further enhance the stress resistance of soldat8 seedlings. Suppression of (1)O2-mediated cell death in young flu/soldat8 seedlings seems to be due to a transiently enhanced acclimation at the beginning of seedling development caused by the initial disturbance of plastid homeostasis.

Arabidopsis glucan synthase-like 10 functions in male gametogenesis

Callose or beta-1,3-glucan performs multiple functions during male and female gametophyte development. Callose is synthesized by 12 members of the glucan synthase-like (GSL) gene family in Arabidopsis thaliana. To elucidate the biological roles of Arabidopsis GSL family members during sexual development, we initiated a reverse genetic approach with T-DNA insertional mutagenesis lines. We screened T-DNA insertion lines for all members of the GSL gene family and detected homozygous mutant seedlings for all members except GSL10. Three independent alleles in GSL10, gsl10-1, gsl10-3 and gsl10-4 showed distorted segregation (1:1:0) of T-DNA inserts rather than Mendelian segregation (1:2:1). By genetic analysis through reciprocal cross, we determined that gsl10 pollen could not be transmitted to descendent. The mutant pollen of GSL10/gsl10 plants at tetrad and microspore stages were not different from that of wild type, suggesting that GSL10 is not essential for normal microspore growth. Analysis of GSL10/gsl10 hemizygous pollen during development revealed abnormal function in asymmetric microspore division. gsl10 mutant microspores failed to enter into mitosis. Unlike the previously described functions of GSL1, GSL2 and GSL5, GSL10 involves an independent process of pollen development at the mitotic division stage.

Comprehensive proteome analysis of lettuce latex using multidimensional protein-identification technology

Commercially, lettuce (Lactuca sativa) is one of the most important leafy vegetables. Lettuce produces a milky latex of variable chemical compositions within its laticifers. As a step toward understanding the main physiological roles of this latex in higher plants, we embarked on its proteomic analysis. We investigated 587 latex proteins that were identified from the lettuce latex using multidimensional protein-identification technology. A bioinformatics analysis showed that the most frequently encountered proteins in the latex were organellar proteins from plastids and mitochondria, followed by nucleic and cytoplasmic proteins. Functional classification of the identified proteins showed that proteins related to metabolism, cell rescue, defense, and virulence were the most abundant in lettuce latex. Furthermore, numerous resistance proteins of lettuce and viral proteins were present in the latex suggesting for the first time a possible function of the lettuce latex in defense or pathogenesis. To the knowledge of the authors, this is the first large-scale proteome analysis of lettuce latex.

A non-cell-autonomous mechanism for the control of plant architecture and epidermal differentiation involves intercellular trafficking of BREVIPEDICELLUS protein

Intercellular trafficking of maize KNOTTED1 and its homologous KNOTTED1-related homeobox (KNOX) proteins has been reported; however, little is known about the functional significance of KNOX trafficking in plant development. In this study, we showed that intercellular movement of BREVIPEDICELLUS (BP or KNAT1), the closest Arabidopsis homologue of KNOTTED1, is tissue-specific and takes place through a selective pathway. When BP was fused to a red fluorescent mCherry construct, it could move from the mesophyll to epidermal cells of leaves, although it could not move out from the cortex/endodermis of roots. Using a trichome rescue-trafficking assay, we also showed that BP fusion could confer gain-of-trafficking function to the cell-autonomous GLABROUS1 (GL1) protein. In the wild type, BP transcripts are expressed in the sub-epidermal cortical cell layers of the inflorescence stem and pedicel. However, bp mutant phenotypes include defects in epidermal cell differentiation suggesting a non-cell-autonomous function. Expression of a GFP:BP fusion under the control of a BP promoter specific to the stem cortex layers resulted in epidermal GFP fluorescence suggesting its movement from subepidermis to epidermis. Here, we provide evidence from complementation analyses using cell autonomous or non-cell-autonomous BP fusions that the intercellular trafficking of BP protein is important for plant architecture and epidermal differentiation.

Cluster analysis and comparison of various chloroplast transcriptomes and genes in Arabidopsis thaliana

Chloroplast RNA metabolism is integrated into wider gene regulatory networks. To explore how, we performed a chloroplast genome-wide expression analysis on numerous nuclear Arabidopsis mutants affected in diverse chloroplast functions and wild-type plants subjected to various stresses and conditions. On the basis of clustering analysis, plastid genes could be divided into two oppositely regulated clusters, largely congruent with known targets of nucleus- and plastid-encoded RNA polymerases, respectively. Further eight sub-clusters contained co-transcribed and functionally tightly associated genes. The chloroplast transcriptomes could also be classified into two major groups comprising mutants preferentially affected in general plastid gene expression and other chloroplast functions, respectively. Deviations from characteristic expression profiles of transcriptomes served to identify novel mutants impaired in accumulation and/or processing of specific plastid RNAs. Expression profiles were useful to distinguish albino mutants affected in plastid gene expression from those with defects in other plastid functions. Remarkably, biotic and abiotic stressors did not define transcriptionally determined clusters indicating that post-transcriptional regulation of plastid gene expression becomes more important under changing environmental conditions. Overall, the identification of sets of co-regulated genes provides insights into the integration of plastid gene expression into common pathways that ensures a coordinated response.

Construction, database integration, and application of an Oenothera EST library

Coevolution of cellular genetic compartments is a fundamental aspect in eukaryotic genome evolution that becomes apparent in serious developmental disturbances after interspecific organelle exchanges. The genus Oenothera represents a unique, at present the only available, resource to study the role of the compartmentalized plant genome in diversification of populations and speciation processes. An integrated approach involving cDNA cloning, EST sequencing, and bioinformatic data mining was chosen using Oenothera elata with the genetic constitution nuclear genome AA with plastome type I. The Gene Ontology system grouped 1621 unique gene products into 17 different functional categories. Application of arrays generated from a selected fraction of ESTs revealed significantly differing expression profiles among closely related Oenothera species possessing the potential to generate fertile and incompatible plastid/nuclear hybrids (hybrid bleaching). Furthermore, the EST library provides a valuable source of PCR-based polymorphic molecular markers that are instrumental for genotyping and molecular mapping approaches.

A plant locus essential for phylloquinone (vitamin K1) biosynthesis originated from a fusion of four eubacterial genes

Phylloquinone is a compound present in all photosynthetic plants serving as cofactor for Photosystem I-mediated electron transport. Newly identified seedling-lethal Arabidopsis thaliana mutants impaired in the biosynthesis of phylloquinone possess reduced Photosystem I activity. The affected gene, called PHYLLO, consists of a fusion of four previously individual eubacterial genes, menF, menD, menC, and menH, required for the biosynthesis of phylloquinone in photosynthetic cyanobacteria and the respiratory menaquinone in eubacteria. The fact that homologous men genes reside as polycistronic units in eubacterial chromosomes and in plastomes of red algae strongly suggests that PHYLLO derived from a plastid operon during endosymbiosis. The principle architecture of the fused PHYLLO locus is conserved in the nuclear genomes of plants, green algae, and the diatom alga Thalassiosira pseudonana. The latter arose from secondary endosymbiosis of a red algae and a eukaryotic host indicating selective driving forces for maintenance and/or independent generation of the composite gene cluster within the nuclear genomes. Besides, individual menF genes, encoding active isochorismate synthases (ICS), have been established followed by splitting of the essential 3' region of the menF module of PHYLLO only in genomes of higher plants. This resulted in inactivation of the ICS activity encoded by PHYLLO and enabled a metabolic branch from the phylloquinone biosynthetic route to independently regulate the synthesis of salicylic acid required for plant defense. Therefore, gene fusion, duplication, and fission events adapted a eubacterial multienzymatic system to the metabolic requirements of plants.

Prmt5, which forms distinct homo-oligomers, is a member of the protein-arginine methyltransferase family

We found that JBP1, known as a human homolog (Skb1Hs) of Skb1 of fission yeast, interacts with NS3 of the hepatitis C virus in a yeast two-hybrid screen. Amino acid sequence analysis revealed that Skb1Hs/JBP1 contains conserved motifs of S-adenosyl-l-methionine-dependent protein-arginine methyltransferases (PRMTs). Here, we demonstrate that Skb1Hs/JBP1, named PRMT5, is a distinct member of the PRMT family. Recombinant PRMT5 protein purified from human cells methylated myelin basic protein, histone, and the amino terminus of fibrillarin fused to glutathione S-transferase. Myelin basic protein methylated by PRMT5 contained monomethylated and dimethylated arginine residues. Recombinant glutathione S-transferase-PRMT5 protein expressed in Escherichia coli also contained the catalytic activity. Sedimentation analysis of purified PRMT5 on a sucrose density gradient indicated that PRMT5 formed distinct homo-oligomeric complexes, including a dimer and tetramer, that comigrated with the enzyme activity. The PRMT5 homo-oligomers were dissociated into a monomer in the presence of a reducing agent, whereas a monomer, dimer, and multimer were detected in the absence or at low concentrations of a reducing agent. The results indicate that both covalent linkage by a disulfide bond and noncovalent association are involved in the formation of PRMT5 homo-oligomers. Western blot analysis of sedimentation fractions suggests that endogenous PRMT5 is present as a homo-oligomer in a 293T cell extract. PRMT5 appears to have lower specific enzyme activity than PRMT1. Although PRMT1 is known to be mainly located in the nucleus, human PRMT5 is predominantly localized in the cytoplasm.

Isolation of functional polarized bile duct units from mouse liver

The development of genetically altered murine animals has generated a need for in vitro systems in the mouse. We have now characterized a novel isolated bile duct unit (IBDU) preparation from the mouse to facilitate such studies. The mouse IBDU is isolated by portal perfusion of collagenase, blunt dissection, further enzymatic digestions, filtering through sized mesh, and culturing on Matrigel for 16-72 h. This mouse IBDU forms a central, enclosed lumen lined by polarized cytokeratin-19-positive cholangiocytes with numerous microvilli on the apical membrane. The IBDU responds to secretory stimuli, including secretin, vasoactive intestinal peptide, IBMX, and forskolin, resulting in expansion of the central lumen from secretion as quantified by videomicroscopy. The secretory response to secretin is dependent on Cl- and HCO3-in the perfusate. These findings indicate that mouse IBDUs are intact, polarized, functional bile duct secretory units that permit quantitative measurements of fluid secretion from mouse bile duct epithelium for the first time. This method should facilitate studies of cholangiocyte secretion in genetically altered murine animal models.

Effects of vitamin A deficiency on rat liver alcohol dehydrogenase expression and alcohol elimination rate in rats

BACKGROUND

Vitamin A has been suggested to regulate the expression of liver alcohol dehydrogenase (ADH) in humans. There are few studies on the ability of retinoic acid to affect ADH expression in vivo and none on its effects on alcohol metabolic rate.

METHODS

Male Sprague Dawley rats were used for isolation of hepatocytes or were rendered vitamin A deficient by feeding a deficient diet for 7 weeks. ADH, retinoic acid receptor beta, and retinoid X receptor alpha protein levels were analyzed by Western blotting. Alcohol elimination rate was determined by following blood alcohol levels after administering a 1.5 g/kg dose of ethanol intraperitoneally.

RESULTS

Retinoic acid had no effect on ADH protein in cultured hepatocytes. In the vitamin A deficient rats, retinol was not detectable in serum or liver at the time animals were killed. ADH and retinoid X receptor alpha protein levels were unchanged in the deficient group compared with a vitamin A sufficient control group, whereas retinoic acid receptor beta levels increased 40%. The deficient rats had a reduced volume of distribution of alcohol, but this largely was accounted for by their smaller body size. The alcohol elimination rates were lower in the deficient animals, but this was accounted for by reduced body and liver weights.

CONCLUSIONS

Severe vitamin A deficiency did not alter liver ADH protein expression or rates of alcohol elimination when expressed per gram of body or liver weight.

Modulation of Starling forces and muscle fiber maturity permits adenovirus-mediated gene transfer to adult dystrophic (mdx) mice by the intravascular route

Duchenne muscular dystrophy (DMD) and other inherited myopathies lead to progressive destruction of most skeletal muscles in the body, including those responsible for maintaining respiration. DMD is a fatal disorder caused by defects in the dystrophin gene. Recombinant adenovirus vectors (AdV) are considered a promising means for therapeutic delivery of a functional dystrophin gene to DMD muscles. If AdV-mediated dystrophin gene replacement in DMD is to be successful, development of a systemic delivery method for targeting the large number of diseased muscles will be required. In this study we investigated two major factors preventing efficient AdV-mediated gene transfer to skeletal muscles of adult animals after intravascular AdV administration: (1) an inability of AdV particles to breach the endothelial barrier and enter into contact with myofibers, and (2) a relatively nonpermissive myofiber population for AdV infection due at least in part to insufficient levels of the coxsackie/adenovirus attachment receptor (CAR). On the basis of established principles governing the transendothelial flux of macromolecules, we further hypothesized that an alteration in Starling forces (increased hydrostatic and decreased osmotic pressures) within the intravascular compartment would facilitate AdV transendothelial flux via convective transport. In addition, experimental muscle regeneration was employed to increase the prevalence of immature myofibers in which CAR expression is upregulated. Here we report that by employing the above-described strategy, high-level heterologous reporter gene expression was achievable in hindlimb muscles of normal rats as well as dystrophic (mdx) mice (genetic homolog of DMD) after a single intraarterial injection of AdV. Microsphere studies confirmed enhanced transport into muscle of fluorescent tracer particles in the size range of AdV, and there was a high concordance between CAR upregulation and myofiber transduction after intraarterial AdV delivery. Furthermore, in mdx mice examined 10 days after intraarterial AdV delivery, the aforementioned procedures had no adverse effects on the force-generating capacity of targeted muscles. These findings have implications for eventual AdV-mediated gene therapy of generalized skeletal muscle diseases such as DMD using a systemic intraarterial delivery approach.

Production and in vitro refolding of a single-chain antibody specific for human plasma apolipoprotein A-I

An active form of single-chain antibody (scFv) has been produced in Escherichia coli for murine monoclonal antibody MabA34 (gamma 1, kappa), which is specific for human plasma apolipoprotein (apo) A-I. The complementary DNAs (cDNAs) encoding the variable regions of heavy chain (VH) and light chain (VL) were connected by a (Gly4Ser)3 linker using an assembly polymerase chain reaction. The construct (VL-linker-VH) was placed under the control of highly efficient T7 promoter system. The cloned scFv was expressed in E. coli as inclusion bodies. After purification from E. coli lysate using sonication and low speed centrifugation, the inclusion body was solubilized and denatured in the presence of 8 M urea, renatured by dialysis, and scFv was finally purified using antigen-affinity chromatography. The purity and activity of purified scFv were confirmed by sodium dodecyl sulfate (SDS)-polyacrylamide gel electrophoresis (PAGE), Western blotting and enzyme-linked immunosorbent assay (ELISA). The affinity constant was determined by a biosensor method using the BIAcore system. The results showed that the yield of correctly refolded scFv was more than 20 mg l-1 of E. coli flask culture and the specific binding activity to apo A-I was retained with an affinity constant of 6.74 x 10(-8) M (Kd). A notable thing is that guanidine-HCl as a denaturant induced more multimeric formation in the subsequent refolding procedure for the scFv of MabA34 and thus, it was not suitable as urea was. This fact is uncommon for what is generally known for the denaturation and refolding of recombinant antibodies.

Vasoactive intestinal polypeptide is a potent regulator of bile secretion from rat cholangiocytes

BACKGROUND & AIMS

Vasoactive intestinal polypeptide (VIP) is a neuropeptide with diverse biological functions including stimulatory effects on bile secretion. The effects of VIP on bile secretion and its site of action were examined.

METHODS

Choleretic effects of VIP were examined using isolated perfused livers, hepatocyte couplets, isolated bile duct units, and cholangiocytes from rat liver.

RESULTS

VIP (100 nmol/L) produced a small increase in bile flow and bile salt output in taurocholate-supplemented isolated perfused livers but had no significant effect on bile flow in the absence of bile salt supplements or on fluid secretion in isolated hepatocyte couplets. In addition, VIP significantly increased bile pH, bicarbonate concentration, and output in the isolated perfused livers from both normal and 2 week bile duct-ligated rats, although bile flow increased only in the bile duct-ligated model. VIP also produced a dose-dependent increase in fluid secretion in isolated bile duct units, which was inhibited significantly by VIP antagonist, a specific VIP receptor inhibitor. This VIP-stimulated secretory response in isolated bile duct units was more potent than those produced by bombesin or secretin. Neither somatostatin nor substance P inhibited the VIP response in isolated bile duct units. In contrast to secretin, VIP had no significant effect on adenosine 3', 5'-cyclic monophosphate (cAMP) levels in isolated cholangiocytes.

CONCLUSIONS

VIP is a potent stimulant of fluid and bicarbonate secretion from cholangiocytes via cAMP-independent pathways, suggesting that this neuropeptide plays a major regulatory role in biliary transport and secretion.

Characterization of ion transport mechanisms involved in bombesin-stimulated biliary secretion in rat cholangiocytes

BACKGROUND/AIMS

Bombesin is a neuropeptide which stimulates fluid and bicarbonate secretion from cholangiocytes by stimulating Cl-/HCO3- exchange. However, the underlying regulation and interactions of ion transporters and channels mediating this bombesin-stimulated biliary secretion are not well characterized. The aim of the study was to characterize the ion transport processes involved in bombesin-stimulated secretion in polarized cholangiocytes in comparison with those of secretin.

METHODS

Isolated bile duct units (IBDU) were prepared from normal rat liver. Biliary secretion induced by bombesin was measured by quantitative video-microscopy in the presence and absence of inhibitors.

RESULTS

Bombesin-stimulated secretion was inhibited by H2-DIDS, NPPB, BaCl2, TEA, and acetazolamide. However, in contrast to secretin, bombesin-stimulated secretion was not inhibited by disruption of microtubules.

CONCLUSIONS

Bombesin-stimulated biliary secretion is dependent on anion exchangers, Cl- and K+ channels, and carbonic anhydrase but not on microtubules. Bombesin regulates secretion in cholangiocytes by different mechanisms from those established for secretin.

Intracellular pH regulation in bombesin-stimulated secretion in isolated bile duct units from rat liver

Bombesin, a neuropeptide, stimulates fluid and HCO-3 secretion from cholangiocytes, but the underlying mechanisms are poorly understood. In this study, we aimed to examine the effects of bombesin on ion transport processes involved in the regulation of intracellular pH (pHi) and HCO-3 secretion in polarized cholangiocytes. Isolated bile duct units from normal rat liver were used to measure pHi by 2', 7'-bis(2-carboxyethyl)-5(6)-carboxyfluorescein 495 nm-to-440 nm dual ratio methods. Bombesin increased Cl--HCO-3 exchange activity but did not affect basal pHi or the activities of Na+/H+ exchange or Na+-HCO-3 symport. Depolarization of cholangiocytes increased basal pHi and the activity of Cl-/HCO-3 exchange, suggesting that an electrogenic Na+-HCO-3 symport might function as a counterregulatory pHi mechanism. Na+-independent acid-extruding mechanisms were not observed. We conclude that bombesin stimulates biliary secretion from cholangiocytes by activating luminal Cl-/HCO-3 exchange, which may be coupled to basolateral electrogenic Na+-HCO-3 symport.

Bombesin stimulates bicarbonate secretion from rat cholangiocytes: implications for neural regulation of bile secretion

BACKGROUND & AIMS

Bombesin is a neuropeptide with many biological functions and is known to stimulate bile secretion. The aim of this study was to determine the role of bombesin in bile secretion and its site of action.

METHODS

The effects of bombesin on bile secretion were examined using isolated perfused rat livers, hepatocyte couplets, and isolated bile duct units (IBDU) from rat liver.

RESULTS

Bombesin (100 nmol/L) increased bile pH, bicarbonate concentration, and output in isolated perfused rat livers from both normal and 2-week bile duct-ligated rats, although bile flow increased only in the latter model. Bombesin (10-100 nmol/L) also had no effect on canalicular bile secretion in isolated hepatocyte couplets. However, bombesin produced a dose-dependent increase in secretion in IBDU, which was inhibited almost completely by a specific bombesin receptor inhibitor, [Tyr4, D-Phe12]-bombesin (1 micromol/L). This bombesin (10 nmol/L)-stimulated secretion in IBDU was accompanied by an increase in luminal pH and was dependent on bicarbonate and chloride in the medium. Somatostatin but not substance P inhibited the bombesin response.

CONCLUSIONS

Neuropeptides such as bombesin can directly stimulate fluid and bicarbonate secretion at the level of cholangiocytes, suggesting that neuropeptides play an important regulatory role in biliary transport and secretion.

Role of the neuropeptide, bombesin, in bile secretion

Since ancient times, bile secretion has been considered vital for maintaining health. One of the main functions of bile secretion is gastric acid neutralization with biliary bicarbonate during a meal or Pavlovian response. Although the liver has many extrinsic and intrinsic nerve innervations, the functional role of these nerves in biliary physiology is poorly understood. To understand the role of neural regulation in bile secretion, our recent studies on the effect of bombesin, a neuropeptide, on bile secretion and its underlying mechanisms will be reviewed. Using isolated perfused rat livers (IPRL) from both normal and 2 week bile duct ligated rats, as well as hepatocyte couplets and isolated bile duct units (IBDU) from normal rat livers, bombesin was shown to stimulate biliary bicarbonate and fluid secretion from bile ducts. Detailed pH studies indicated that bombesin stimulated the activity of Cl-/HCO3- exchanger, which was counterbalanced by a secondary activation of electrogenic Na+/HCO3- symport. Quantitative videomicroscopic studies showed that bombesin-stimulated fluid secretion in IBDU was dependent on Cl- and HCO3- in the media, anion exchanger(s), Cl- and K+ channels, and carbonic anhydrase, but not on the microtubular system. Furthermore, this bombesin response is inhibited by somatostatin but not substance P. Finally, studies of secondary messengers in isolated cholangiocytes and IBDU indicated that bombesin had no effect on intracellular cAMP, cGMP, or Ca++ levels in cholangiocytes. These results provide evidence that neuropeptides such as bombesin can directly stimulate fluid and bicarbonate secretion from cholangiocytes by activating luminal Cl-/HCO3- exchange, but by different mechanisms from those established for secretin. These findings, in turn, suggest that neuropeptides may play an important regulatory role in biliary transport and secretion. Thus, this neuropeptidergic regulation of bile secretion may provide a plausible mechanism for the bicarbonate-rich choleresis seen with meals or Pavlovian response.

Cloning and characterization of cDNAs coding for heavy and light chains of a monoclonal antibody (MabA34) specific for human plasma apolipoprotein A-I

We have determined the nucleotide (nt) sequences encoding the heavy (H)- and light (L)-chains of the Fab fragment of a murine monoclonal antibody, MabA34 (gamma1, kappa), which is specific for human plasma apolipoprotein A-I of high-density lipoproteins. The variable (V) regions of the H- and L-chains were revealed to be members of mouse H-chain subgroup II(A) and kappa L-chain subgroup II, respectively. A few unusual amino acids in the V region of the H-chain, and nt residues probably introduced by somatic mutations from germline genes were also identified.

Cloning and characterization of cDNAs coding for heavy and light chains of a monoclonal antibody (MabB23) specific for human plasma apolipoprotein B-100

We have determined the nucleotide sequences encoding the heavy and light chains of the Fab fragment of murine monoclonal antibody MabB23(gamma2b,lambda), which is specific for human plasma apolipoprotein B-100 of low-density lipoproteins. The sequence analyses revealed that the variable regions of the heavy and light chains are members of mouse heavy-chain subgroup I(B) and lambda light-chain, respectively. A few unusual amino acids in the framework and constant regions of the heavy-chain were also noticed.

Blockade of noradrenergic neurotransmission with diethyldithiocarbamic acid decreases the mRNA level of gonadotropin-releasing hormone in the hypothalamus of ovariectomized, steroid-treated prepubertal rats

We have previously found that progesterone (P) augmented gonadotropin-releasing hormone (GnRH) mRNA levels in the hypothalamus of ovariectomized, estradiol-treated (OVX + E) prepubertal rats. In order to determine whether noradrenergic neurotransmission is involved in the stimulatory effect of P on GnRH gene expression, diethyldithiocarbamic acid (DDC, 500 mg/kg), a dopamine beta-hydroxylase inhibitor was administered i.p. 1 h before P (1 mg) injection into OVX + E treated rats, and the effect of DDC on the P-induced GnRH mRNA levels was examined. A single injection of P into OVX + E primed rats augmented norepinephrine (NE) content, while the administration of DDC effectively blocked the P-induced increase in NE content, along with the increase in dopamine content. Suppression of NE neurotransmission with DDC resulted in a marked decrease in the P-induced GnRH mRNA levels as well as GnRH release in vitro. These results clearly demonstrate that noradrenergic neurotransmission is involved in P-stimulated GnRH gene expression in the rat hypothalamus.

Effect of secretion on intracellular pH regulation in isolated rat bile duct epithelial cells

The effects of secretin on ion transport mechanisms involved in regulation of intracellular pH (pHi) and HCO3- excretion were characterized in bile duct epithelial (BDE) cells isolated from normal rat liver. pHi was measured with 2,7-bis(carboxy-ethyl)-5(6)-carboxy-fluorescein-acetomethylester (BCECF-AM) using a microfluorimetric method. Basal pHi of BDE was 7.04 +/- 0.06 in Hepes and 7.16 +/- 0.10 in KRB and was unaffected by secretin (50-200 nM). Recovery rates from an acid load in Hepes or in KRB media (with and without amiloride) were also not altered by secretin, indicating that Na+/H+ exchange and Na+/HCO3- cotransport were not affected by this hormone. After acute Cl- removal, pHi rose 0.24 +/- 0.08 pHU at a maximal rate of 0.125 +/- 0.06 pHU/min (H+ flux rates = 6.02 +/- 3.27 mM/min) and recovered after Cl- readmission (0.188 +/- 0.08 pHU/min; H+ flux rates = 11.82 +/- 5.34 mM/min). Pretreatment with 1 mM DIDS inhibited the effects of Cl- removal, while valinomycin, which induces cell depolarization, enhanced these effects, probably by stimulating electrogenic HCO3- influx. Secretin significantly increased both the maximal rate of alkalinization after Cl- removal (P < 0.012) and of pHi recovery after Cl- readmission (P < 0.025), indicating stimulation of Cl-/HCO3- exchange activity. These findings were reproduced with N6,2'-O-Dibutyryladenosine-3',5'-cyclic monophosphate (DBcAMP). The Cl- channel blocker 5-nitro-2'-(3-phenylpropylamino)-benzoate (NPPB, 10 microM) significantly decreased the effects of secretin and DBcAMP on the pHi changes promoted by acute Cl- removal/readmission. These findings establish that secretin stimulates the activity of the Cl-/HCO3- exchanger in BDE cells, probably by activating Cl- channels via the intracellular messenger cAMP. This in turn depolarizes the cell, stimulating electrogenic Na+/HCO3- symport. The cell depolarization induced by Cl- channel activation should enhance HCO3- entrance through electrogenic Na+/HCO3- symport, which in turn stimulates the Cl-/HCO3- exchange. These mechanisms could account for secretin stimulated bicarbonate secretion in bile.

A partial blockade of catecholaminergic neurotransmission with 6-hydroxydopamine decreases mRNA level of gonadotropin releasing hormone in the male rat hypothalamus

Central catecholamines (CA) are known to be involved in the regulation of synthesis and secretion of gonadotropin releasing hormone (GnRH) from the hypothalamus. However, no attempt has been yet made to determine whether CA affects GnRH gene expression. To this end, the effect of 6-hydroxydopamine (6-OHDA), a catecholaminergic neurotoxin, on GnRH mRNA level was examined. Hypothalamic tissues obtained from adult male rats were incubated with medium containing 6-OHDA. To ensure the effect of 6-OHDA on CA depleting action, CA levels in media and in postincubation tissues were determined. Increasing concentrations of 6-OHDA resulted in decrease in norepinephrine (NE) and dopamine (DA) contents in a dose dependent manner. Treatment with 6-OHDA (5 x 10(-4) M produced a time-dependent decrease in NE but not DA, when CA levels in media were determined at 30 min intervals during the incubation period. To determine changes in GnRH mRNA level in response to 6-OHDA treatment in vitro, for 2.5 h total cytoplasmic RNA fractions were isolated from postincubation hypothalamic tissues and used for RNA-blot hybridization with 32P-labeled GnRH riboprobe. A blockade of CA neurotransmission with 6-OHDA (5 x 10(-4) M) significantly reduced GnRH mRNA level by half over its control and internal control (actin mRNA) groups. Northern blot analysis revealed that addition of NE (1 x 10(-6) M) reversed the decreased GnRH mRNA level by 6-OHDA.(ABSTRACT TRUNCATED AT 250 WORDS)

Inhibitory effect of purines in meiotic maturation of denuded mouse oocytes

The potential action of purines, such as hypoxanthine and adenosine, in meiotic arrest was examined using denuded mouse oocytes. The spontaneous meiotic maturation of denuded oocytes was significantly inhibited by hypoxanthine and/or adenosine in a dose-dependent manner. Germinal vesicle breakdown (GVBD) was inhibited even at a low concentration (1 nM) of hypoxanthine, when hypoxanthine was microinjected into the cytoplasm of denuded oocytes. This inhibitory action was potentiated by co-injection with allopurinol, a metabolic blocker of hypoxanthine that can block a metabolic pathway to uric acid. By contrast, a microinjection of adenosine was no longer effective in inhibiting GVBD. Inhibitory action of purines in meiotic maturation was correlated with sustaining intracellular cAMP levels. GVBD was resumed by econazole, one of the nitroimidazole derivatives which act as inhibitors of catalytic subunit of adenylate cyclase. This compound was effective in counteracting the effect of adenosine, but not the action of 3-isobutyl-1-methylxanthine (IBMX) on GVBD, indicating that adenosine is probably exerted at the level of oocyte plasmalemma. These data suggest that the inhibitory action of hypoxanthine and adenosine in oocyte meiotic maturation may be involved in the regulation of cAMP metabolism in a differential manner.

Adrenergic mediation of the naloxone-induced GnRH release from hypothalami of ovariectomized, steroid-treated immature rats

The present study examines the effect of naloxone on GnRH release in vitro under different steroid milieus. Naloxone (6.1 mumol/kg) administered 30 min before decapitation was highly effective in evoking GnRH release from superfused hypothalamic tissues derived from ovariectomized, estradiol- and progesterone-treated immature rats, while ineffective in altering GnRH release from intact, ovariectomized and vehicle- or estradiol-treated rats. To further explore the possible involvement of catecholamines in the naloxone-stimulated GnRH release, diethyldithiocarbamic acid (2.9 mmol/kg), an inhibitor of noradrenalin synthesis, was administered ip 30 min before naloxone injection into ovariectomized, estradiol- and progesterone-treated rats. Diethyldithiocarbamic acid markedly reduced the naloxone-evoked GnRH release, although it was ineffective in modifying the spontaneous release of GnRH. A blockade of alpha-adrenergic receptor with phenoxybenzamine significantly suppressed the naloxone-stimulated GnRH release, whereas treatment with propranolol, a beta-adrenergic receptor blocker, failed to alter GnRH release. The present data suggest that the endogenous opioid peptide may participate in the regulation of GnRH release under a particular steroid milieu, and the inhibitory action of endogenous opioid peptide seems to require the mediation of adrenergic neurotransmission, presumably through alpha-adrenergic receptor.

Protein modification by phosphorylation during the process of nuclear membrane dissolution in puromycin-treated mouse oocytes

The present study was undertaken to elucidate the mechanism of nuclear membrane dissolution (NMD) in puromycin-treated mouse oocytes. Treatment of germinal vesicle breakdown (GVBD) oocytes with puromycin (50 micrograms/ml) induced chromosome decondensation with formation of a polar body; these are designated nuclear membrane (NM) oocytes. After withdrawal of puromycin, NM oocytes underwent NMD (approximately 70%) during a 12-h culture period. Either dibutyryl cyclic AMP (dbcAMP, 25-100 micrograms/ml) or isobutylmethylxanthine (IBMX, 0.1-1.0 mM) inhibited the process of NMD in a dose-dependent manner, suggesting the involvement of cAMP in the process of NMD. To determine which protein(s) participated in the transition from interphase to metaphase II during NMD, NM oocytes were labeled with [35S]methionine, and one- and two-dimensional gel electrophoresis were performed. Although the synthesis of stage-specific proteins during NMD was not found, two specific proteins of Mr 27,000 and 46,000, which were synthesized at interphase following removal of puromycin, were modified during NMD. Phosphatase treatment and 32PO4-labeling experiments indicated that phosphorylation was responsible for these modifications, which were inhibited by either dbcAMP or IBMX. Therefore, it appears that phosphorylation of specific proteins may play an important role in the transition from interphase to metaphase II.