NF-kappaB determines localization and features of cell death in epidermis.

Specialized forms of physiologic cell death lacking certain characteristic morphologic features of apoptosis occur in terminally differentiating tissues, such as in the outer cell layers of epidermis. In these cell layers, NF-kappaB translocates from the cytoplasm to the nucleus and induces target gene expression. In light of its potent role in regulating apoptotic cell death in other tissues, NF-kappaB activation in these cells suggests that this transcription factor regulates cell death during terminal differentiation. Here, we show that NF-kappaB protects normal epithelial cells from apoptosis induced by both TNFalpha and Fas, whereas NF-kappaB blockade enhances susceptibility to death via both pathways. Expression of IkappaBalphaM under control of keratin promoter in transgenic mice caused a blockade of NF-kappaB function in the epidermis and provoked premature spontaneous cell death with apoptotic features. In normal tissue, expression of the known NF-kappaB-regulated antiapoptotic factors, TRAF1, TRAF2, c-IAP1, and c-IAP2, is most pronounced in outer epidermis. In transgenic mice, NF-kappaB blockade suppressed this expression, whereas NF-kappaB activation augmented it, consistent with regulation of cell death by these NF-kappaB effector proteins. These data identify a new role for NF-kappaB in preventing premature apoptosis in cells committed to undergoing physiologic cell death and indicate that, in stratified epithelium, such cell death normally proceeds via a distinct pathway that is resistant to NF-kappaB and its antiapoptotic target effector genes.

Nuclear factor kappaB subunits induce epithelial cell growth arrest.

Nuclear factor kappaB (NF-kappaB) gene-regulatory proteins play important roles in inflammation, neoplasia, and programmed cell death. Recently, blockade of NF-kappaB function has been shown to result in epithelial hyperplasia, suggesting a potential role for NF-kappaB in negative growth regulation. We expressed active NF-kappaB subunits in normal epithelial cells and found that NF-kappaB profoundly inhibits cell cycle progression. This growth inhibition is resistant to mitogenic stimuli and is accompanied by other features of irreversible growth arrest. NF-kappaB-triggered cell cycle arrest is also associated with selective induction of the cyclin-dependent kinase inhibitor p21CiP1, with overexpression of p21(Cip1) alone inducing findings similar to those seen with NF-kappaB in vitro. An active NF-kappaB subunit expressed in the epidermis of p21(CiP1-/- mice, however, displays only partial growth-inhibitory effects, suggesting that full NF-kappaB growth inhibition is only partially p21(Cip1) dependent in this setting. These data indicate that NF-kappaB can trigger cell cycle arrest in epithelial cells in association with selective induction of a cell cycle inhibitor.

Comparative Studies on S-Glycoproteins Purified from Different S-Genotypes in Self-Incompatible BRASSICA Species I. Purification and Chemical Properties.

S-glycoproteins, i.e. stigma glycoproteins that are heritable in correlation with S allele in self-incompatible Brassica species, were apparently purified for three S alleles in B. oleracea. From SDS gel electrophoresis, the estimated molecular weight for two of the S-glycoproteins was 57,000. The other S-glycoprotein was considered to be heterogeneous with molecular weights of 60,000 and 65,000. Distinct differences in amino acid content were found; in general, cysteine, methionine and histidine were low, and serine, glutamate, glycine, leucine, arginine and aspartate were high and variable between the S-glycoproteins. Differences in the isoelectric point were mainly attributed to the amino acid composition of each S-glycoprotein.

Comparative Studies on S-Glycoproteins Purified from Different S-Genotypes in Self-Incompatible BRASSICA Species II. Immunological Specificities.

Antisera were prepared by immunization of apparently purified S-glycoproteins; one from an S allele of Brassica campestris and two from S alleles of B. oleracea. Each antiserum was reactive not only with the homologous S-glycoprotein but also with the heterologous ones, i.e. with the S-glycoproteins of the other S alleles of the same locus. In double diffusion tests, a spur against the heterologous S-glycoproteins suggested heterogeneity of the glycoproteins. The heterogeneity appears to involve a component of the molecule in which the genotypic specificity of an S-glycoprotein resides, probably, for the recognition site. Some molecular components are common to all tested S-glycoproteins and in this respect are like the public antigens of the MHC locus of mammals. The common molecular components were recognized between the S-allele-specific glycoproteins within B. oleracea and also between them and those of B. campestris. No S-specific substances were detected in buffer soluble homogenates of style, ovary or anther. However, these homogenates contained substances that had structures similar to the corresponding common parts of the S-glycoproteins.

Molecular characterization of S locus genes, SLG and SRK, in a pollen-recessive self-incompatibility haplotype of Brassica rapa L.

In Brassica species that exhibit self-incompatibility, two genes, SLG and SRK, at the S locus are involved in the recognition reaction with self and non-self pollen. From a pollen-recessive S29 haplotype of Brassica rapa, both cDNA and genomic DNA clones for these two genes were isolated and characterized. The nucleotide sequence for the S domain of SRK29 showed a high degree of similarity with that of SLG29, and they belong to Class II type. RNA gel blot analysis showed that the transcript of SLG29 consisted of the first and second exons, and no other transcript containing any part of the intron sequence was detected. Because no transmembrane domain was encoded by the second exon of SLG29, SLG29 was designated a secreted type glycoprotein. SLGs of two other pollen-recessive haplotypes, S40 and S44, of B. rapa also had a similar structure to that of SLG29. Previously, SLG2 from a pollen-recessive haplotype, S2, of Brassica oleracea was found to produce two different transcripts, one for the secreted type glycoprotein and the other for a putative membrane-anchored form of SLG. Therefore, the nature of these SLGs from pollen-recessive haplotypes of B. rapa is different from that of SLG2 of B. oleracea.

Evolutionary aspects of the S-related genes of the Brassica self-incompatibility system: synonymous and nonsynonymous base substitutions.

In the Brassicaceae, self-vs. nonself-recognition in self-incompatibility is controlled by sporophytic S-alleles. Haplotypes specifying both SRK (S-receptor kinase) and SLG (S-locus glycoprotein) are considered to play an important role in the recognition reactions. We compared the nucleotide sequences of SRK9(Bc) and SRK6(Bo). The number of nonsynonymous substitutions per site (Pn) was lower, constrained, in the kinase than the receptor domain, while the numbers of synonymous substitutions (Ps) in the two domains were largely comparable. Pairwise values for Ps and Pn were calculated among 17 operational taxonomic units, including eight SLGs, the receptor domains of two SRKs, four SRAs (S-related A) and three SRBs (S-related B), which have high homologies with each other. The values of Ps and Pn of SLG were mostly comparable to those of the receptor domain of SRK. Dendrograms constructed on the basis of Pn and Ps indicated that SRA differentiated first, followed by SRB. The differentiation of SLG alleles is one of prerequisite factors for the establishment of self-incompatibility, and the allelic differentiation has occurred more than tens of million years ago.

Isolation and characterization of fission yeast sns mutants defective at the mitosis-to-interphase transition.

pim1-d1ts was previously identified in a visual screen for fission yeast mutants unable to complete the mitosis-to-interphase transition. pim1+ encodes the guanine nucleotide exchange factor (GEF) for the spi1 GTPase. Perturbations of this GTPase system by either mutation or overproduction of its regulatory proteins cause cells to arrest with postmitotic condensed chromosomes, an unreplicated genome, and a wide medial septum. The septation phenotype of pim1-d1ts was used as the basis for a more extensive screen for this novel class of sns (septated, not in S-phase) mutants. Seventeen mutants representing 14 complementation groups were isolated. Three strains, sns-A3, sns-A5, and sns-A6, representing two different alleles, are mutated in the pim1+ gene. Of the 13 non-pim1ts sns complementation groups, 11 showed genetic interactions with the spi1 GTPase system. The genes mutated in 10 sns strains were synthetically lethal with pim1-d1, and six sns strains were hypersensitive to overexpression of one or more of the known components of the spil GTPase system. Epistasis analysis places the action of the genes mutated in nine of these strains downstream of pim1+ and the action of one gene upstream of pim1+. Three strains, sns-A2, sns-B1, and sns-B9, showed genetic interaction with the spil GTPase system in every test performed. sns-B1 and sns-B9 are likely to identify downstream targets, whereas sns-A2 is likely to identify upstream regulators of the spi1 GTPase system that are required for the mitosis-to-interphase transition.

Genomic organization of the S locus: Identification and characterization of genes in SLG/SRK region of S(9) haplotype of Brassica campestris (syn. rapa).

In Brassica, two self-incompatibility genes, encoding SLG (S locus glycoprotein) and SRK (S-receptor kinase), are located at the S locus and expressed in the stigma. Recent molecular analysis has revealed that the S locus is highly polymorphic and contains several genes, i.e., SLG, SRK, the as-yet-unidentified pollen S gene(s), and other linked genes. In the present study, we searched for expressed sequences in a 76-kb SLG/SRK region of the S(9) haplotype of Brassica campestris (syn. rapa) and identified 10 genes in addition to the four previously identified (SLG(9), SRK(9), SAE1, and SLL2) in this haplotype. This gene density (1 gene/5.4 kb) suggests that the S locus is embedded in a gene-rich region of the genome. The average G + C content in this region is 32.6%. An En/Spm-type transposon-like element was found downstream of SLG(9). Among the genes we identified that had not previously been found to be linked to the S locus were genes encoding a small cysteine-rich protein, a J-domain protein, and an antisilencing protein (ASF1) homologue. The small cysteine-rich protein was similar to a pollen coat protein, named PCP-A1, which had previously been shown to bind SLG.

Involvement of Phenolic Esters in Cell Aggregation of Suspension-Cultured Rice Cells.

Fluorescence microscopy of rice (Oryza sativa L.) callus sections showed that all of the walls fluoresced blue in water (pH 5.8) and green in ammonia (pH 10.0), both characteristics of feruloyl esters. Such fluorescence in the walls of cells cultured in Gamborg's B5 medium was much stronger than that in amino acid (AA) medium. Laser scanning microscopy showed that the level of fluorescence was higher in the intercellular layer, especially at corner junctions between cells, suggesting that ferulic acid ester derivatives are located in the middle lamella as well as in the wall. Extracellular polysaccharides appearing during cultivation in AA medium were more highly feruloylated than those in B5 medium during cultivation. Both the levels of ferulic and diferulic acid and the relative proportion of diferulic acid in the walls of cells increased on transfer of the cells cultured in AA medium to B5 medium. The walls of cells cultured in B5 medium maintained constant levels and proportions of the phenolic acids. Removal of phenolic acids from wall preparations by carboxylesterase facilitated the solubilization of noncellulosic polysaccharides. Treatment of the cell aggregates grown in AA medium with an enzyme that hydrolyzes feruloyl esters decreased the size of the aggregates to between 20 and 500 [mu]m, compared with an original size between 200 and 1000 [mu]m. These findings suggest that feruloyl and diferuloyl esters between polysaccharides are involved in the aggregation of cultured rice cells.

Characterization of expressed genes in the SLL2 region of self-compatible Arabidopsis thaliana.

Self-incompatibility in Brassica species is regulated by a set of S-locus genes: SLG, SRK, and SP11/SCR. In the vicinity of the S-locus genes, several expressed genes, SLL2 and SP2/ClpP, etc., were identified in B. campestris. Arabidopsis thaliana is a self-compatible Brassica relative, and its complete genome has been sequenced. From comparison of the genomic sequences between B. campestris and A. thaliana, microsynteny between gene clusters of Arabidopsis and Brassica SLL2 regions was observed, though the S-locus genes, SLG, SRK, and SP11/SCR were not found in the region of Arabidopsis. Almost all genes predicted in this region of Arabidopsis were expressed in both vegetative and reproductive organs, suggesting that the genes in the SLL2 region might not be related to self-incompatibility. Considering the recent speculation that the S-locus genes were translocated as a single unit between Arabidopsis and Brassica, the translocation might have occurred in the region between the SLL2 and SP7 genes.

Highly conserved 5'-flanking regions of two self-incompatibility genes, SLG9 and SRK9.

The nucleotide (nt) sequences of the 5'-flanking regions of two Brassica self-incompatibility genes, SLG9 and SRK9, were determined. Their sequences were highly conserved: a region spanning 1.9 kb in the 5'-flanking region was completely identical except for a 1319-bp segment in SLG9. These observations strongly suggest that SLG9 and SRK9 together with their promoter regions were involved in a gene duplication or conversion event which occurred before the 1319-bp SLG9-specific sequence was inserted in SLG9 or deleted in SRK9.

Direct cloning of the Brassica S locus by using a P1-derived artificial chromosome (PAC) vector.

Self-incompatibility of Brassica is regulated by the S locus, which contains several genes including SLG and SRK. We found that both SLG and SRK genes were located at an approx. 80-kb MluI fragment in an S9 haplotype of B. campestris. Therefore, we cloned this MluI fragment into a BssHII site of the P1-derived artificial chromosome (PAC) vector. The utility of the direct cloning method is discussed in this study.

Highly divergent sequences of the pollen self-incompatibility (S) gene in class-I S haplotypes of Brassica campestris (syn. rapa) L.

Self-incompatibility (SI) enables flowering plants to discriminate between self- and non-self-pollen. In Brassica, SI is controlled by the highly polymorphic S locus. The recently identified male determinant, termed SP11 or SCR, is thought to be the ligand of S receptor kinase, the female determinant. To examine functional and evolutionary properties of SP11, we cloned 14 alleles from class-I S haplotypes of Brassica campestris and carried out sequence analyses. The sequences of mature SP11 proteins are highly divergent, except for the presence of conserved cysteines. The phylogenetic trees suggest possible co-evolution of the genes encoding the male and female determinants.

The SLGs corresponding to the same S24-haplotype are perfectly conserved in three different self-incompatible Brassica campestris L.

We have identified three strains of the same S24-haplotype in self-incompatible B. campestris L. Two of them, S-12j and 1-1j, have been derived from Japanese populations and one, 27-1t, from Turkish one. The cDNA clones of SLG24 (S24-locus glycoprotein), which linked to the S-locus, were isolated from each strain, and sequenced. Each clone isolated from S-12j, 1-1j and 27-1t, was designated as SLG24 (S-12j), SLG24 (1-1j) and SLG24 (27-1t), respectively. Their nucleotide sequences were completely identical in coding region, 5' non-coding region, and 3' non-coding region, though the position of the polyadenylation site was slightly different among the cDNA clones. This result suggests that the origin of S24-haplotype in these three strains might be common, and that the nucleotide sequences of SLG24 of the same S24-haplotype are completely conserved among different populations. The high conservation of the SLG24 nucleotide sequences is probably essential for the recognition of self or non-self of self-incompatibility in this S24-haplotype.

Tapetum-specific expression of theOsg6B promoter-ß-glucuronidase gene in transgenic rice.

The promoter of an anther tapetum-specific gene,Osg6B, was fused to aß-glucuronidase (GUS) gene and introduced into rice byAgrobacterium-mediated gene transfer. Fluorometric and histochemical GUS assay showed that GUS was expressed exclusively within the tapetum of anthers from the uninucleate microspore stage (7 days before anthesis) to the tricellular pollen stage (3 days before anthesis). This is the first demonstration of an anther-specific promoter directing tapetum-specific expression in rice.

Con A - Peroxidase method: an improved procedure for staining S-glycoproteins in cellulose-acetate electrofocusing in crucifers.

In the analysis of stigma glycoproteins by cellulose acetate electrofocusing in self-incompatible crucifers, the staining method of the glycoproteins, described in the earlier report, has been improved by using Con A - peroxidase reactions to obtain a permanent profile of band patterns which are visible under day-light conditions. Identifying S alleles by the corresponding S-glycoproteins can be facilitated by the present S-glycoprotein analysis.

Repressing the expression of self-incompatibility in crucifers by short-term high temperature treatment.

The effect of short-term high temperature on the expression of self-incompatibility was studied in detached flowers of Brassica oleracea, B. campestris and Raphanus sativus. The expression of self-incompatibility was repressed by treatment of pistils at 40 °C for 15 minutes. Treatment at 50 °C repressed self-incompatibility but it also disturbed pollen tube elongation into stylar tissue. S-glycoproteins did not show any quantitative changes during the intact pistil treatment under 50 °C. Callose was occasionally found in the treated papilla where the self pollen tube penetrated. The repressing effect of the 40 °C treatment was found to be reversible, and this reversibility depended upon the environmental temperature of plant. Plants grown at 15/5 °C (day/night temperature) completely recovered self-incompatibility 2 h after treatment, while those grown at 20/10°, 25/15 °C did not. The reversibility of the expression of self-incompatibility correlated with the distortion of plasma membrane in the papilla. It is considered that high temperature affects the pollen tube penetration system in pistils rather than the recognition system between pistils and pollen. The treatment of dehiscing anthers at 40 °C killed the pollen.

Diploid somatic-hybrid plants regenerated from rice cultivars.

Somatic hybrid plants were obtained between rice cultivars 'Yamahoushi' and 'Murasakidaikoku'. Since 'Murasakidaikoku' is a double mutant having both dominant (purple coloration) and recessive (dwarf) markers, the somatic hybrids can be easily distinguished from their parents. Protoplasts were isolated from anther-derived calli, and electrofused protoplasts were cultured without selection of hybrid cells. Out of 27 regenerated plants, 9 proved to be hybrids based on their purple coloration and normal plant type, traits which were identical to those of the sexual F1 hybrid between the same parental cultivars. The somatic hybrids included three diploid and six triploid plants. Segregation of parental markers was observed in the selfed progenies. These results demonstrated that diploid hybrids of rice could be obtained through somatic hybridization between haploid anther-derived cells instead of by sexual hybridization.