XIPHOPHORUS ENZYME GENE EXPRESSION: TISSUE SPECIFICITY, GENETIC CONTROL, AND STABILITY IN CULTURED CELLS

Five permanent cell lines were developed from Xiphophorus maculatus, X. helleri, and their hybrids using three tissue sources, including adults and embryos of different stages. To evaluate cell line gene expression for retention of either tissue-of-origin-specific or ontogenetic stage-specific characters, the activity distribution of 44 enzyme loci was determined in 11 X. maculatus tissues, and the developmental genetics of 17 enzyme loci was charted in X. helleri and in helleri x maculatus hybrids using starch gel electrophoresis. In the process, eight new loci were discovered and characterized for Xiphophorus.^ No Xiphophorus cell line showed retention of tissue-of-origin-specific or ontogenetic stage-specific enzyme gene expressional traits. Instead, gene expression was similar among the cell lines. One enzyme, adenosine deaminase (ADA) was an exception. Two adult-origin cell lines expressed ADA, whereas, three cell lines derived independently from embryos did not. ADA('-) expression of Xiphophorus embryo-derived cell lines may represent retention of an embryonic gene expressional trait. In one cell line (T(,3)) derived from 13 pooled interspecific hybrid (F(,2)) embryos, shifts with time were observed at enzyme loci polymorphic between the two species. This suggested shifts in ratios of cells of different genotypes in the population rather than unstable gene expression in one dominant cell type.^ Verification of this hypothesis was attempted by cloning the culture--seeking clones having different genetic signatures. The large number of loci electrophoretically polymorphic between the two species and whose alleles segregated independently into the 13 progeny from which this culture originated almost guaranteed the presence of different genetic signatures (lineages) in T(,3).^ Seven lineages of cells were found within T(,3), each expressing genotypes at some loci not characteristic of the expression of the culture-as-a-whole, supporting the hypothesis tested. Quantitative studies of ADA expression in the whole culture (ADA('-)) and in clones of these seven lineages suggested the predominance in T(,3) of ADA deficient cell lineages, although moderate to high ADA output clones also occurred. Thus, T(,3) has the potential to shift phenotypes from ADA('-) to ADA('+) by simply changing proportions of its constituent cell types, demonstrating that such shifts can occur in any cell culture containing cells of mixed expressional characteristics.^

Molecular and evolutionary genetics of the X -linked visual pigment genes in humans and New World monkeys

Normal humans have one red and at least one green visual pigment genes. These genes are tightly linked as tandem repeats on the X chromosome and each of them has six exons. There is only one X-linked visual pigment gene in New World monkeys (NWMs) but the locus has three polymorphic alleles encoding red, yellow and green visual pigments, respectively. The spectral properties of the squirrel monkey and the marmoset (both NWMs) have been studied and partial sequences of the three alleles are available. To study the evolutionary history of these X-linked opsin genes in humans and NWMs, coding and intron sequences of the three squirrel monkey alleles and the three marmoset alleles were amplified by PCR followed by subcloning and sequencing. Introns 2 and 4 of the human red and green pigment genes were also sequenced. The results obtained are as follows: (1) The sequences of introns 2 and 4 of the human red and green opsin genes are significantly more similar between the two genes than are coding sequences, contrary to the usual situation where coding regions are better conserved in evolution than are introns. The high similarities in the two introns are probably due to recent gene conversion events during evolution of the human lineage. (2) Phylogenetic analysis of both intron and exon sequences indicates that the phylogenetic tree of the available primate opsin genes is the same as the species tree. The two human genes were derived from a gene duplication event after the divergence of the human and NWM lineages. The three alleles in each of the two NWM species diverged after the split of the two NWMs but have persisted in the population for at least 5 million years. (3) Allelic gene conversion might have occurred between the three squirrel monkey alleles. (4) A model of additive effect of hydroxyl-bearing amino acids on spectral tuning is proposed by treating some unknown variables as groups. Under the assumption that some residues have no effect, it is found that at least five amino acid residues, at positions 178 (3 nm), 180 (5 nm), 230 ($-$4 nm), 277 (9 nm) and 285 (13 nm), have linear spectral tuning effects. (5) Adaptive evolution of the opsin genes to different spectral peaks was observed at four residues that are important for spectral tuning. ^

Cloning and molecular analysis of paraxis: A {\it trans\/}-acting factor required for somite maturation

During vertebrate embryogenesis, cells from the paraxial mesoderm coalesce in a rostral-to-caudal progression to form the somites. Subsequent compartmentalization of the somites yields the sclerotome, myotome and dermatome, which give rise to the axial skeleton, axial musculature, and dermis, respectively. Recently, we cloned a novel basic-Helix-Loop-Helix (bHLH) protein, called scleraxis, which is expressed in the sclerotome, in mesenchymal precursors of bone and cartilage, and in connective tissues. This dissertation focuses on the cloning, expression and functional analysis of a bHLH protein termed paraxis, which is nearly identical to scleraxis within the bHLH region but diverges in both its amino and carboxyl termini. During the process of mouse embryogenesis, paraxis transcripts are first detected at about day 7.5 post coitum within the primitive mesoderm lying posterior to the head and heart primordia. Subsequently, paraxis expression progresses caudally through the paraxial mesoderm, immediately preceding somite formation. Paraxis is expressed at high levels in newly formed somites before the first detectable expression of the myogenic bHLH genes, and as the somite becomes compartmentalized, paraxis becomes downregulated within the myotome.^ To determine the function of paraxis during mammalian embryogenesis, mice were generated with a null mutation in the paraxis locus. Paraxis null mice survived until birth, but exhibited severe foreshortening along the anteroposterior axis due to the absence of vertebrae caudal to the midthoracic region. The phenotype also included axial skeletal defects, particularly shortened bifurcated ribs which were detached from the vertebral column, fused vertebrae and extensive truncation and disorganization caudal to the hindlimbs. Mutant neonates also lacked normal levels of trunk muscle and exhibited defects in the dermis as well as the stratification of the epidermis. Analysis of paraxis -/- mutant embryos has revealed a failure of the somites to both properly epithelialize and compartmentalize, resulting in defects in somite-derived cell lineages. These results suggest that paraxis is an essential component of the genetic pathway regulating somitogenesis. ^

Functional analysis of the sea urchin {\it orthodenticle\/} -related gene, {\it SPOTX\/}, in aboral ectoderm-specific gene activation and aboral ectoderm cell fate specification

An important question in developmental biology is how embryonic cell types are derived from a fertilized egg. To address this question, this thesis investigates the mechanisms by which the aboral ectoderm-specific Spec2a gene is spatially and temporally regulated during sea urchin embryogenesis. The Spec2a gene of the sea urchin Strongylocentratus purpuratus has served as a valuable maker to understand the basis of lineage-specific gene activation and the role of transcription factors in cell fate specification. The hypothesis is that transcription factors responsible for cell type-specific gene activation are key components in the initial cell specification step. The Spec2a gene, which encodes a small cytosolic calcium-binding protein, is expressed exclusively in aboral ectoderm cell lineages. The 1516-bp control region of the Spec2a gene contains a 188-bp enhancer element required for temporal activation and aboral ectoderm/mesenchyme cell expression, while an unidentified element upstream of the enhancer represses expression in mesenchyme cells. Using an enhancer activation assay, combined with site-directed mutagenesis, I showed that three TAATCC/T sites within the enhancer are responsible for enhancer activity. Mutagenizing these sites and a fourth one just upstream abolished all activity from the Spec2a control region. A 77-bp DNA fragment from the Spec2a enhancer containing two of the TAATCC/T sites is sufficient for aboral ectoderm/mesenchyme cell expression. A cDNA encoding SpOtx, an orthodenticle-related protein, was cloned from S. purpuratus and shown to bind with high affinity to the TAATCC/T sequences within the Spec2a control region. SpOtx transcripts were found initially in all cells of the cleaving embryo, but they gradually became restricted to oral ectoderm and endoderm cells, suggesting that SpOtx might play a role in the initial temporal activation of the Spec2a gene and most likely has additional functions in the developing embryo. To reveal the broader biological functions of SpOtx, I injected SpOtx mRNA into living sea urchin eggs to determine what effects overexpressing the SpOtx protein might have on embryo development. SpOtx mRNA-injected embryos displayed dramatic alterations in development. Instead of developing into pluteus larvae with 15 different cell types, uniform epithelia balls were formed. These balls consisted of a thin layer of squamous cells with short cilia highly reminiscent of aboral ectoderm. Immunohistochemical staining and RT-PCR demonstrated that the SpOtx-injected embryoids expressed aboral ectoderm markers uniformly, but showed very weak or no expression of markers for non-aboral ectoderm cell types. These data strongly suggested that overexpression of SpOtx redirected the normal fate of non-aboral ectoderm cells to that of aboral ectoderm. These results show that SpOtx is involved in aboral ectoderm differentiation by activating aboral ectoderm-specific genes and that modulating its expression can lead to changes in cell fate. ^

Functions of GCN5 and P /CAF acetyltransferases in mammalian development

Histone acetyltransferases are important chromatin modifiers that function as transcriptional co-activators. The identification of the transcriptional regulator GCN5 as the first nuclear histone acetyltransferase in yeast directly linked chromatin remodeling to transcriptional regulation. Although emerging evidence suggests that acetyltransferases participate in multiple cellular processes, their roles in mammalian development remain undefined. In this study, I have cloned and characterized the mouse homolog of GCN5 and a closely related protein P/CAF that interacts with p300/CBP. In contrast to yeast GCN5, but similar to P/CAF, mouse GCN5 possesses an additional N-terminal domain that confers the ability to acetylate nucleosomal histones. GCN5 and P/CAF exhibit identical substrate specificity and both interact with p300/CBP. Interestingly, expression levels of GCN5 and P/CAF display a complementary pattern in mouse embryos and in adult tissues, suggesting that they have distinct tissue or developmental stage specific roles. To define the in vivo function of GCN5 and P/CAF, I have generated mice that are nullizygous for GCN5 or P/CAF. P/CAF null mice are viable and fertile with no gross morphological defects, indicating that P/CAF is dispensable for development and p300/CBP function in vivo. In contrast, mice lacking GCN5 die between 10.5–11 days of gestation. GCN5 null mice are severely retarded but have anterior ectopic outgrowth. Molecular marker analyses reveal that early mesoderm is formed in GCN5 null mice but further differentiation into distinct mesodermal lineages is perturbed. While presomitic mesoderm and chodamesoderm are missing in GCN5 mutant mice, extraembryonic tissues and lateral mesoderm are unaffected. This is consistent with our finding that GCN5 expression is absent in the heart and extraembryonic tissues but is uniform throughout the rest of the embryo. Remarkably, GCN5 mutant mice exhibit an unusually high incidence of apoptosis in the embryonic ectoderm and mesoderm. Finally, mice doubly null for GCN5 and P/CAF die much earlier than mice harboring the GCN5 mutation alone, suggesting that P/CAF and GCN5 share some overlapping function during embryogenesis. This work is the first study to show that specific acetyltransferase is important for cell survival as well as mesoderm differentiation or maintenance during early mammalian development. ^

Isolation and characterization of a novel human Mix -like homeobox gene MIXL

Molecular events involved in specification of early hematopoietic system are not well known. In Xenopus, a paired-box homeodomain family (Mix.1–4) has been implicated in this process. Although Mix-like homeobox genes have been isolated from zebrafish (bon), chicken (CMIX) and mice (MmI/MIXL1), isolation of a human Mix-like gene has remained elusive. ^ We have recently isolated and characterized a novel human Mix-like homeobox gene with a predicted open reading frame of 232 amino acids designated the Mix.1 homeobox (Xenopus laevis)-like gene (MIXL). The overall identity of this novel protein to CMIX and MmI/MIXL1 is 41% and 69%, respectively. However, the identity in the homeodomain is 66% to that of Xenopus Mix.1, 79% to that of CMIX, and 94% to that of MmI/MIXL1. In normal hematopoiesis, MIXL expression appears to be restricted immature B and T lymphoid cells. Several acute leukemic cell lines of B, T and myeloid lineages express MIXL suggesting a survival/block in differentiation advantage. Furthermore, Xenopus animal cap assay revealed that MIXL could induce expression of the α-globin gene, suggesting a functional conservation of the homeodomain. ^ Biochemical analysis revealed that MIXL proteins are phosphorylated at multiple sites. Immunoprecipitation and immunoblotting confirmed that MIXL is tyrosine phosphorylated. Mutational analysis determined that Tyr20 appears to be the site for phosphorylation. However, deletion analysis preliminarily showed that the proline-rich domain appears not to be necessary for tyrosine phosphorylation. The novel finding will help us make a deeper understanding of the regulation on homeodomain proteins by rarely reported tyrosine phosphorylation. ^ Taken together, isolation of the MIXL gene is the first step toward understanding novel regulatory circuits in early hematopoietic differentiation and malignant transformation. ^

Planktonic foraminifera in the latest Maastrichtian of Walvis Ridge, South Atlantic

An abrupt global warming of 3-4°C occurred near the end of the Maastrichtian at 65.45-65.10 Ma. The environmental effects of this warm event are here documented based on stable isotopes and quantitative analysis of planktonic foraminifera at the South Atlantic DSDP Site 525A. Stable isotopes of individual species mark a rapid increase in temperature and a reduction in the vertical water mass stratification that is accompanied by a decrease in niche habitats, reduced species diversity and/or abundance, smaller species morphologies or dwarfing, and reduced photosymbiotic activity. During the warm event, the relative abundance of a large number of species decreased, including tropical-subtropical affiliated species, whereas typical mid-latitude species retained high abundances. This indicates that climate warming did not create favorable conditions for all tropical-subtropical species at mid-latitudes and did not cause a massive retreat in the local mid-latitude population. A noticeable exception is the ecological generalist Heterohelix dentata Stenestad that dominated during the cool intervals, but significantly decreased during the warm event. However, dwarfing is the most striking response to the abrupt warming and occurred in various species of different morphologies and lineages (e.g. biserial, trochospiral, keeled globotruncanids). Dwarfing is a typical reaction to environmental stress conditions and was likely the result of increased reproduction rates. Similarly, photosymbiotic activity appears to have been reduced significantly during the maximum warming, as indicated by decreased delta13C values. The foraminiferal response to climate change is thus multifaceted resulting in decreased species diversity, decreased species populations, increased competition due to reduced niche habitats, dwarfing and reduced photosymbiotic activity.

Planktonic foraminifera of Oligocene sediments from DSDP Hole 77-538A in the Gulf of Mexico

A relatively extended Oligocene pelagic sequence with good to medium recovery, drilled during DSDP Leg 77 in the Gulf of Mexico, yielded rich and well diversified planktonic foraminiferal faunas. Planktonic foraminifera recorded in Hole 538A span the interval from Zone P19 through P22. Evolutionary lineages were observed among the globoquadrinids, the globigerinitids, and the "Globigerina" ciperoensis and Globigerinoides primordius groups. Quantitative analysis of planktonic foraminiferal assemblages shows that faunas fluctuate in abundance and species diversity throughout the sequence. A few of these fluctuations that could be related to selective dissolution are mainly confined to the early-mid Oligocene. A climatic curve was constructed using as warmer indicators, Turborotalia pseudoampliapertura, Globoquadrina tripartita, Dentoglobigerina globularis, Dentoglobigerina baroemoenensis,. "Globigerina" ciperoensis and Globigerinoides groups, and Cassigerinella chipolensis; and as coller indicators, Catapsydrax spp., Globorotaloides spp., Subbotina angiporoides group, Globigerina s. str., and the tenuitellides. Three major intervals are identifiable in the climatic curve: Interval 1 (lower) up to Zone P20 predominantly cooler: Interval 2 (intermediate) up to the upper part of Zone P21a with warm and cool fluctuations: and lnterval 3 (upper), warmer, with a large positive peak, due to abundant "G." angulisuturalis, at the beginning of Zone P21b with recooling midway in Zone P22. In Intervals 1 and 2 planktonic foraminiferal faunas are dominated by temperate forms. Interpretation of planktonic foraminiferal data suggests that cooler water conditions characterize the early-mid Oligocene: during the mid Oligocene (most of Zone P21a) water masses exhibit peculiar characteristics transitional to the warmer waters prevailing during the late Oligocene. Warmer conditions were not definitely settled in Zone P22, however, as indicated by the cooler episode following the warmest peak. These climatic trends are inconsistent with those inferred from oxygen isotopes except at small scale. In fact, oxygen isotope values for Oligocene Atlantic Ocean are too heavy (thus too cool) in comparison with the high abundance and diversity of warm taxa, expecially in Zone P22. When values are lighter (warmer), as in Zone P19 abundance and diversity of warm indices are too low. To explain such a cool isotope values in presence of highly diversified and abundant warm planktonic foraminifera, we suggest (1) that the oxygen isotope ratio used for estimating Oligocene paleotemperatures might be 1? heavier than Eocene values and further increased for the late Oligocene. This hypothesis implies the presence of a relatively extended ice cap in Antarctica in the early and mid Oligocene, and probably an increase in ice volume during the late Oligocenc: (2) heavier isotope values might be related to an increase in salinity, or (3) by a combination of both ice cap and increase in salinity.

(Table S1) Molecular analyses and morphological comparisons of deep-sea clams

Large vesicomyid clams are common inhabitants of sulphidic deep-sea habitats such as hydrothermal vents, hydrocarbon seeps and whale-falls. Yet, the species- and genus-level taxonomy of these diverse clams has been unstable due to insufficiencies in sampling and absence of detailed taxonomic studies that would consistently compare molecular and morphological characters. To clarify uncertainties about species-level assignments, we examined DNA sequences from mitochondrial cytochrome-c-oxidase subunit I (COI) in conjunction with morphological characters. New and published COI sequences were used to create a molecular database for 44 unique evolutionary lineages corresponding to species. Overall, the congruence between molecular and morphological characters was good. Several discrepancies due to synonymous species designations were recognized, and acceptable species names were rectified with published COI sequences in cases where morphological specimens were available. We identified seven species with trans-Pacific distributions, and two species with Indo-Pacific distributions. Presently, 27 species have only been documented from one region, which might reflect limited ranges, or insufficient geographical sampling. Vesicomyids exhibit the greatest species diversity along the northwest Pacific ridge systems and in the eastern Pacific, along the western America margin, where depth zonation typically results in segregation of closely related species. The broad distributions of several vesicomyid species suggest that their required chemosynthetic habitats might be more common than previously recognized and occur along most continental margins.

Escribir el desierto. Narrar la nación. Literatura y periodismo en la formación de la nación argentina, 1830-1852

Esta tesis indaga en los textos escritos por la llamada generación del 37 (o "generación romántica" argentina) en el período de dominio rosista en el Río de la Plata (1830-1852). Se estudia el proceso simbólico de formación de una tradición y un canon literario nacional desde una perspectiva que toma en cuenta tanto los cruces genéricos como el contexto de enunciación de los distintos discursos analizados. En la primera parte, "Escribir (en) el desierto", se analiza el tratamiento del paisaje como forma simbólica en La cautiva de Echeverría, en el marco de los tópicos de la literatura de viaje de la época, y, en la segunda sección, los primeros ensayos dedicados a la formación de una literatura nacional en los periódicos románticos (La Moda, El Zonda, El Iniciador). En la segunda parte, "El tejido biográfico", se aborda el Facundo y el discurso modernizador de Sarmiento; en la tercera, "Linajes, memorias, influencias", se estudia la discusión sobre los límites de la nacionalidad a partir de las Investigaciones sobre la influencia social de la conquista y el sistema colonial de los españoles en Chile de José Victorino Lastarria, memoria presentada en 1844 en la Universidad de Chile, y a la que responden, desde distintos posicionamientos, Bello, Sarmiento y Alberdi.

Villas y aldeas en el Antiguo Régimen : Conflicto y consenso en el marco local castellano

Las villas y aldeas de Castilla recorrieron juntas un largo y difícil camino desde los siglos medievales, cuando se fueron conformando como cuerpos políticos, basados en servicios recíprocos que aspiraban a alcanzar el bien común del conjunto. La naturaleza jerárquicamente desigual de dicho cuerpo fue acentuándose y las cabezas jurisdiccionales llevaron a la práctica unas relaciones de dominio cada vez más acusado frente a las aldeas. En estas comunidades rurales, linajes en ascenso aspiraban, no obstante, a ampliar sus propias cotas de autogobierno. La armonía que debía presidir el cuerpo común de villas y aldeas fue desapareciendo, y la política regia de ventas de villazgos con fines hacendísticos, iniciada por Carlos V, respondió a una demanda de segregación que solucionaba al mismo tiempo las aspiraciones jurisdiccionales de las comunidades rurales y de sus nuevas oligarquías así como las necesidades de ingresos extraordinarios de la real hacienda

Relaciones ciudad-aldea en Trasmiera y la zona Oriental de Cantabria : Linajes, parentelas y clientelas en el marco del señorío de los Condestables (siglos XIV-XVI)

El presente artículo tiene como objetivo analizar la dinámica que adquieren las relaciones de dominio señorial al interior del señorío de la Casa de los Velasco, Condestables hereditarios del reino de Castilla, partiendo de la forma que adopta la intrincada red de agentes y administradores señoriales a su servicio ubicados en el nivel de las aldeas y villas que forman parte de la zona oriental de Cantabria entre los siglos XIV al XVI. Para ello, estableceremos los diversos mecanismos de solidaridad, dependencia y sujeción de los cuales se vale el señor para ejercer su jurisdicción y poder de mando sobre este conjunto plural de comunidades y hombres. Es decir, nuestra intención es estudiar el proceso de construcción del poder señorial a partir de una imagen dinámica que le brinde dimensión y profundidad y que, al mismo tiempo, permita entender la constitución del dominio político señorial no sólo como una imposición de arriba hacia abajo, sino también como un espacio de negociación en permanente rearticulación que involucra tanto al señor, su parentela y clientela, como a las comunidades jerarquizadas, tanto rurales como urbanas, que se encuentran sometidas a su poder

Escribir el desierto. Narrar la nación. Literatura y periodismo en la formación de la nación argentina, 1830-1852

Esta tesis indaga en los textos escritos por la llamada generación del 37 (o "generación romántica" argentina) en el período de dominio rosista en el Río de la Plata (1830-1852). Se estudia el proceso simbólico de formación de una tradición y un canon literario nacional desde una perspectiva que toma en cuenta tanto los cruces genéricos como el contexto de enunciación de los distintos discursos analizados. En la primera parte, "Escribir (en) el desierto", se analiza el tratamiento del paisaje como forma simbólica en La cautiva de Echeverría, en el marco de los tópicos de la literatura de viaje de la época, y, en la segunda sección, los primeros ensayos dedicados a la formación de una literatura nacional en los periódicos románticos (La Moda, El Zonda, El Iniciador). En la segunda parte, "El tejido biográfico", se aborda el Facundo y el discurso modernizador de Sarmiento; en la tercera, "Linajes, memorias, influencias", se estudia la discusión sobre los límites de la nacionalidad a partir de las Investigaciones sobre la influencia social de la conquista y el sistema colonial de los españoles en Chile de José Victorino Lastarria, memoria presentada en 1844 en la Universidad de Chile, y a la que responden, desde distintos posicionamientos, Bello, Sarmiento y Alberdi.

Villas y aldeas en el Antiguo Régimen : Conflicto y consenso en el marco local castellano

Las villas y aldeas de Castilla recorrieron juntas un largo y difícil camino desde los siglos medievales, cuando se fueron conformando como cuerpos políticos, basados en servicios recíprocos que aspiraban a alcanzar el bien común del conjunto. La naturaleza jerárquicamente desigual de dicho cuerpo fue acentuándose y las cabezas jurisdiccionales llevaron a la práctica unas relaciones de dominio cada vez más acusado frente a las aldeas. En estas comunidades rurales, linajes en ascenso aspiraban, no obstante, a ampliar sus propias cotas de autogobierno. La armonía que debía presidir el cuerpo común de villas y aldeas fue desapareciendo, y la política regia de ventas de villazgos con fines hacendísticos, iniciada por Carlos V, respondió a una demanda de segregación que solucionaba al mismo tiempo las aspiraciones jurisdiccionales de las comunidades rurales y de sus nuevas oligarquías así como las necesidades de ingresos extraordinarios de la real hacienda

Relaciones ciudad-aldea en Trasmiera y la zona Oriental de Cantabria : Linajes, parentelas y clientelas en el marco del señorío de los Condestables (siglos XIV-XVI)

El presente artículo tiene como objetivo analizar la dinámica que adquieren las relaciones de dominio señorial al interior del señorío de la Casa de los Velasco, Condestables hereditarios del reino de Castilla, partiendo de la forma que adopta la intrincada red de agentes y administradores señoriales a su servicio ubicados en el nivel de las aldeas y villas que forman parte de la zona oriental de Cantabria entre los siglos XIV al XVI. Para ello, estableceremos los diversos mecanismos de solidaridad, dependencia y sujeción de los cuales se vale el señor para ejercer su jurisdicción y poder de mando sobre este conjunto plural de comunidades y hombres. Es decir, nuestra intención es estudiar el proceso de construcción del poder señorial a partir de una imagen dinámica que le brinde dimensión y profundidad y que, al mismo tiempo, permita entender la constitución del dominio político señorial no sólo como una imposición de arriba hacia abajo, sino también como un espacio de negociación en permanente rearticulación que involucra tanto al señor, su parentela y clientela, como a las comunidades jerarquizadas, tanto rurales como urbanas, que se encuentran sometidas a su poder