RESUMEN
The growth of pollen tubes to plant egg cells and the guidance of axons to neural synapses are classic examples of targeted cell growth. Despite the evolutionary time that separates animals and plants, axon and pollen tube guidance share remarkable mechanistic similarities. In both instances, extracellular cues are transduced by intracellular signal-transduction pathways that culminate in directed tip growth. Do the mechanistic similarities extend to the molecular level? Here, we address this question by a comprehensive review of the molecules and pathways involved in pollen tube targeting and axon guidance. The emerging scenario is that similar intracellular molecules are recruited to control tip growth, while different extracellular molecules mediate guidance through the distinct plant and animal extracellular matrices.
Asunto(s)
Axones/fisiología , Quimiotaxis , Fenómenos Fisiológicos de las Plantas , Polen/fisiología , Animales , Calcio/metabolismo , Citoesqueleto/metabolismo , Transducción de Señal , Proteínas de Unión al GTP rho/metabolismoRESUMEN
We characterized the yeast actin cytoskeleton at the ultrastructural level using immunoelectron microscopy. Anti-actin antibodies primarily labeled dense, patchlike cortical structures and cytoplasmic cables. This localization recapitulates results obtained with immunofluorescence light microscopy, but at much higher resolution. Immuno-EM double-labeling experiments were conducted with antibodies to actin together with antibodies to the actin binding proteins Abp1p and cofilin. As expected from immunofluorescence experiments, Abp1p, cofilin, and actin colocalized in immuno-EM to the dense patchlike structures but not to the cables. In this way, we can unambiguously identify the patches as the cortical actin cytoskeleton. The cortical actin patches were observed to be associated with the cell surface via an invagination of plasma membrane. This novel cortical cytoskeleton-plasma membrane interface appears to consist of a fingerlike invagination of plasma membrane around which actin filaments and actin binding proteins are organized. We propose a possible role for this unique cortical structure in wall growth and osmotic regulation.
Asunto(s)
Actinas/ultraestructura , Membrana Celular/ultraestructura , Citoesqueleto/ultraestructura , Saccharomyces cerevisiae/ultraestructura , Actinas/metabolismo , Ciclo Celular , Membrana Celular/metabolismo , Endocitosis , Proteínas de Microfilamentos/metabolismo , Microscopía Fluorescente , Microscopía Inmunoelectrónica , Ósmosis , Saccharomyces cerevisiae/metabolismoRESUMEN
In flowering plants, a series of cell-cell interactions govern the delivery of sperm to the ovules through precise guidance of pollen tubes. Two Arabidopsis genes, POP2 and POP3, were found that mediate pollen tube guidance and are critical for self-fertility in diploid reproductive cells. The pop2 and pop3 mutations exhibited genetic redundancy: Self-sterility occurred only when male and female tissues were defective in both genes. This phenotype resembles that found in many self-incompatible species.
Asunto(s)
Arabidopsis/fisiología , Genes de Plantas , Polen , Arabidopsis/genética , Arabidopsis/ultraestructura , Cruzamientos Genéticos , Marcadores Genéticos , Genotipo , Microscopía Electrónica de Rastreo , Mutación , Fenotipo , ReproducciónRESUMEN
Two Arabidopsis thaliana genes, QRT1 and QRT2, are required for pollen separation during normal development. In qrt mutants, the outer walls of the four meiotic products of the pollen mother cell are fused, and pollen grains are released in tetrads. Pollen is viable and fertile, and the cytoplasmic pollen contents are discrete. Pollination with a single tetrad usually yields four seeds, and genetic analysis confirmed that marker loci segregate in a 2:2 ratio within these tetrads. These mutations allow tetrad analysis to be performed in Arabidopsis and define steps in pollen cell wall development.
Asunto(s)
Arabidopsis/genética , Genes de Plantas , Polen/fisiología , Arabidopsis/fisiología , Arabidopsis/ultraestructura , Pared Celular/ultraestructura , Mapeo Cromosómico , Marcadores Genéticos , Glucuronidasa/genética , Heterocigoto , Meiosis , Microscopía Electrónica de Rastreo , Mutación , Fenotipo , Polen/ultraestructuraRESUMEN
In the process of protein secretion, amino-terminal signal sequences are key recognition elements; however, the relation between the primary sequence of an amino-terminal peptide and its ability to function as an export signal remains obscure. The limits of variation permitted for functional signal sequences were determined by replacement of the normal signal sequence of Saccharomyces cerevisiae invertase with essentially random peptide sequences. Since about one-fifth of these sequences can function as an export signal the specificity with which signal sequences are recognized must be very low.
Asunto(s)
Glicósido Hidrolasas/metabolismo , Señales de Clasificación de Proteína/fisiología , Secuencia de Aminoácidos , Citoplasma/enzimología , Espacio Extracelular/enzimología , Glicosilación , Saccharomyces cerevisiae/enzimología , Saccharomyces cerevisiae/metabolismo , Relación Estructura-Actividad , beta-FructofuranosidasaRESUMEN
The pollen extracellular matrix contains proteins mediating species specificity and components needed for efficient pollination. We identified all proteins >10 kilodaltons in the Arabidopsis pollen coating and showed that most of the corresponding genes reside in two genomic clusters. One cluster encodes six lipases, whereas the other contains six lipid-binding oleosin genes, including GRP17, a gene that promotes efficient pollination. Individual oleosins exhibit extensive divergence between ecotypes, but the entire cluster remains intact. Analysis of the syntenic region in Brassica oleracea revealed even greater divergence, but a similar clustering of the genes. Such allelic flexibility may promote speciation in plants.
Asunto(s)
Proteínas de Arabidopsis , Arabidopsis/genética , Lipasa/química , Familia de Multigenes , Proteínas de Plantas/química , Polen/química , Proteoma , Alelos , Secuencias de Aminoácidos , Secuencia de Aminoácidos , Arabidopsis/química , Brassica/química , Brassica/genética , Etiquetas de Secuencia Expresada , Genes de Plantas , Variación Genética , Genoma de Planta , Lipasa/genética , Datos de Secuencia Molecular , Fosfotransferasas/química , Fosfotransferasas/genética , Proteínas de Plantas/genética , Estructura Terciaria de Proteína , Reacción en Cadena de la Polimerasa de Transcriptasa Inversa , Alineación de SecuenciaRESUMEN
High-precision genetic mapping was used to define the regions that contain centromere functions on each natural chromosome in Arabidopsis thaliana. These regions exhibited dramatic recombinational repression and contained complex DNA surrounding large arrays of 180-base pair repeats. Unexpectedly, the DNA within the centromeres was not merely structural but also encoded several expressed genes. The regions flanking the centromeres were densely populated by repetitive elements yet experienced normal levels of recombination. The genetically defined centromeres were well conserved among Arabidopsis ecotypes but displayed limited sequence homology between different chromosomes, excluding repetitive DNA. This investigation provides a platform for dissecting the role of individual sequences in centromeres in higher eukaryotes.
Asunto(s)
Arabidopsis/genética , Centrómero/genética , ADN de Plantas/genética , Genes de Plantas , Recombinación Genética , Secuencias Repetitivas de Ácidos Nucleicos , Arabidopsis/química , Composición de Base , Secuencia de Bases , Centrómero/fisiología , Secuencia Conservada , Mapeo Contig , Cruzamientos Genéticos , Intercambio Genético , ADN de Plantas/química , Expresión Génica , Meiosis , Modelos Genéticos , Retroelementos , Análisis de Secuencia de ADNRESUMEN
INTRODUCTION: Duplicated ureteral anatomy can be a reconstructive challenge. Blind-ending ureteral duplication has been reported with recommendations for surgical excision. OBJECTIVE: This video reviews the importance of exposure of anatomic landmarks in surgical excision of a blind-ending ureteral duplication. MATERIALS AND METHODS: This is a retrospective case report of a patient who presented with a blind-ending ureteral duplication. DISCUSSION: A 13-year-old female presented with a right-sided abdominal mass. Abdominal and pelvic imaging revealed a tubular structure adjacent to and below the right kidney, possibly connecting to the right lower pole. While initially observed, the patient re-presented with urosepsis. A retrograde pyelogram showed no connection between the right ureter and this structure. The patient underwent robotic-assisted excision of this structure. Intra-operatively, it was connected to the right lower pole calyces. A ureteroureterostomy to the orthotopic ureter was performed. Although the structure was adjacent to the bladder dome, there was no communication distally. Postoperatively, the patient did well; follow-up imaging showed a non-dilated lower pole. The pathology of this structure was benign urothelium. CONCLUSIONS: Surgical management of aberrant ureteral duplications should focus on identifying known landmarks and should be considered to prevent symptomatic infections and renal scarring.
Asunto(s)
Procedimientos Quirúrgicos Robotizados , Uréter/anomalías , Uréter/cirugía , Ureterostomía/métodos , Adolescente , Femenino , Humanos , Estudios RetrospectivosRESUMEN
Reproduction in flowering plants requires a series of interactions between the haploid and diploid phases of the life cycle of the plant. Mutations that affect these interactions have been identified in Arabidopsis, thus giving insight into the processes of gamete development and pollination. These studies promise to yield new information on diverse topics in plant biology, from cell-cell recognition to the evolution of mating interactions.
Asunto(s)
Arabidopsis/fisiología , Arabidopsis/genética , Células Germinativas , Polen , Reproducción/genéticaRESUMEN
Several secretion-defective variants of invertase from Saccharomyces cerevisiae were generated by replacement of the wild-type signal sequence codons with DNA fragments with random sequences. Strains encoding these proteins failed to grow on medium containing sucrose as the sole source of carbon. The invertase that was made in these strains was found to fractionate with soluble, cytoplasmic proteins, and indirect immunofluorescence confirmed that the mutant invertase was located throughout the cytoplasm. To define the defects in the secretion-defective leader sequences, we selected revertants by requiring growth on sucrose. Surprisingly, most of the reversion events consisted of point changes and duplications in the upstream noncoding portion of the gene. Each of these changes introduced several hydrophobic residues into the nonfunctional leader sequences, suggesting that the defective random leader peptides might simply lack adequate hydrophobicity to be effective signal peptides.
Asunto(s)
Glicósido Hidrolasas/genética , Señales de Clasificación de Proteína/genética , Saccharomyces cerevisiae/genética , Secuencia de Aminoácidos , Mapeo Cromosómico , Genes Fúngicos , Variación Genética , Glicósido Hidrolasas/metabolismo , Datos de Secuencia Molecular , Mutación , Saccharomyces cerevisiae/enzimología , beta-FructofuranosidasaRESUMEN
The membrane compartments responsible for Golgi functions in wild-type Saccharomyces cerevisiae were identified and characterized by immunoelectron microscopy. Using improved fixation methods, Golgi compartments were identified by labeling with antibodies specific for alpha 1-6 mannose linkages, the Sec7 protein, or the Ypt1 protein. The compartments labeled by each of these antibodies appear as disk-like structures that are apparently surrounded by small vesicles. Yeast Golgi typically are seen as single, isolated cisternae, generally not arranged into parallel stacks. The location of the Golgi structures was monitored by immunoelectron microscopy through the yeast cell cycle. Several Golgi compartments, apparently randomly distributed, were always observed in mother cells. During the initiation of new daughter cells, additional Golgi structures cluster just below the site of bud emergence. These Golgi enter daughter cells at an early stage, raising the possibility that much of the bud's growth might be due to secretory vesicles formed as well as consumed entirely within the daughter. During cytokinesis, the Golgi compartments are concentrated near the site of cell wall synthesis. Clustering of Golgi both at the site of bud formation and at the cell septum suggests that these organelles might be directed toward sites of rapid cell surface growth.
Asunto(s)
Ciclo Celular , Proteínas Fúngicas/metabolismo , Aparato de Golgi/ultraestructura , Compuestos de Manganeso , Saccharomyces cerevisiae/ultraestructura , Transporte Biológico , Compartimento Celular , Proteínas Fúngicas/inmunología , Aparato de Golgi/metabolismo , Inmunohistoquímica , Manganeso , Glicoproteínas de Membrana/inmunología , Glicoproteínas de Membrana/metabolismo , Microscopía Electrónica , Óxidos , Saccharomyces cerevisiae/crecimiento & desarrollo , Saccharomyces cerevisiae/metabolismo , Coloración y EtiquetadoRESUMEN
The Saccharomyces cerevisiae Cdc42 protein, a member of the Ras superfamily of low-molecular-weight GTP-binding proteins, is involved in the control of cell polarity during the yeast cell cycle. This protein has a consensus sequence (CAAX) for geranylgeranyl modification and is likely to be associated, at least in part, with cell membranes. Using cell fractionation and immunolocalization techniques, we have investigated the subcellular localization of Cdc42p. Cdc42p was found in both soluble and particulate pools, and neither its abundance nor its distribution varied through the cell cycle. The particulate form of Cdc42p could be solubilized with detergents but not with NaCl or urea, suggesting that it is tightly associated with membranes. An increase in soluble Cdc42p was observed in a geranylgeranyltransferase mutant strain (cdc43-2ts) grown at the restrictive temperature. In addition, Cdc42p from a cdc42C188S mutant strain (that has an alteration at the prenylation consensus site) was almost exclusively in the soluble fraction, suggesting that membrane localization is dependent on geranylgeranyl modification at Cys-188. Immunofluorescence and immunoelectron microscopy experiments demonstrated that Cdc42p localizes to the plasma membrane in the vicinity of secretory vesicles that were found at the site of bud emergence, at the tips and sides of enlarging buds, and within mating projections (shmoo tips) in alpha-factor-arrested cells. These results indicate that Cdc42p is localized to the bud site early in the cell cycle and suggest that this localization is critical for the selection of the proper site for bud emergence and for polarized cell growth.
Asunto(s)
Polaridad Celular , Proteínas Fúngicas/análisis , Proteínas de Unión al GTP/análisis , Saccharomyces cerevisiae/química , Fracciones Subcelulares/química , Secuencia de Aminoácidos , Ciclo Celular , Secuencia de Consenso , Proteínas Fúngicas/fisiología , Proteínas de Unión al GTP/fisiología , Datos de Secuencia Molecular , Procesamiento Proteico-Postraduccional , Reproducción Asexuada , Saccharomyces cerevisiae/fisiología , Saccharomyces cerevisiae/ultraestructura , Proteína de Unión al GTP cdc42 de Saccharomyces cerevisiaeRESUMEN
The centromeres of higher plants and animals share many common features, though current models fail to account for all aspects of centromere composition and function. This dilemma is likely to be resolved in the next few years in Arabidopsis where robust assays for centromere function are available and the sequence of the entire genome will be determined.
Asunto(s)
Arabidopsis/genética , Centrómero/genética , Genoma de Planta , Animales , Centrómero/fisiología , Células Eucariotas , HumanosRESUMEN
Recent work has revealed signaling molecules that control pollination, including small peptides that mediate pollen recognition and glycoproteins that support pollen tube growth. The polarized growth of pollen tubes requires a calcium-mediated signal cascade, and cues derived from the haploid and diploid ovule cells guide pollen tubes to the eggs.
Asunto(s)
Fenómenos Fisiológicos de las Plantas , Polen , Polaridad Celular , Fertilización , Células Vegetales , Plantas/embriología , SemillasRESUMEN
The comprehensive analysis of the genome sequence of the plant Arabidopsis thaliana has been completed recently. The genome sequence and associated analyses provide the foundations for rapid progress in many fields of plant research, such as the exploitation of genetic variation in Arabidopsis ecotypes, the assessment of the transcriptome and proteome, and the association of genome changes at the sequence level with evolutionary processes. Nevertheless, genome sequencing and analysis are only the first steps towards a new plant biology. Much remains to be done to refine the analysis of encoded genes, to define the functions of encoded proteins systematically, and to establish new generations of databases to capture and relate diverse data sets generated in widely distributed laboratories.
Asunto(s)
Arabidopsis/genética , Genoma de Planta , Arabidopsis/metabolismo , Proteínas de Plantas/fisiología , Análisis de Secuencia de ADNRESUMEN
The identification of the antigenic stimuli of B-cell neoplasms might be of considerable importance since a causal relationship between these neoplasms and antigenic stimulation has been suggested. To date the identification of such antigens has been erratic and accidental. For a systematic search and molecular characterization of human proteins that are antigenic target structures of myeloma-associated immunoglobulins, we applied SEREX (serological analysis of antigens by recombinant cDNA expression cloning) using a testis cDNA expression library and myeloma proteins from 42 patients. A monoclonal IgA from a female patient was shown to target sperm-specific cylicin II. The specificity of the reaction was confirmed by the characteristic staining of the equatorial belt of human sperm heads by the patient's myeloma protein. Serological analysis of recombinantly expressed cDNAs is a straightforward and high throughput approach for the molecular characterization of the targets of myeloma-associated immunoglobulins. The analysis of the antigenic spectrum of immunoglobulins associated with B-cell neoplasms will provide valuable information for the understanding of the pathogenesis of these diseases.