Arabidopsis and Medicago truncatula represent sister clades within the dicot subclass Rosidae. We used genetic map-based and bacterial artificial chromosome sequence-based approaches to estimate the level of synteny between the genomes of these model plant species. Mapping of 82 tentative orthologous gene pairs reveals a lack of extended macrosynteny between the two genomes, although marker collinearity is frequently observed over small genetic intervals. Divergence estimates based on non-synonymous nucleotide substitutions suggest that a majority of the genes under analysis have experienced duplication in Arabidopsis subsequent to divergence of the two genomes, potentially confounding synteny analysis. Moreover, in cases of localized synteny, genetically linked loci in M. truncatula often share multiple points of synteny with Arabidopsis; this latter observation is consistent with the large number of segmental duplications that compose the Arabidopsis genome. More detailed analysis, based on complete sequencing and annotation of three M. truncatula bacterial artificial chromosome contigs suggests that the two genomes are related by networks of microsynteny that are often highly degenerate. In some cases, the erosion of microsynteny could be ascribed to the selective gene loss from duplicated loci, whereas in other cases, it is due to the absence of close homologs of M. truncatula genes in Arabidopsis.Comparative genetic mapping has revealed a high degree of conservation in genome structure among closely related plant species, in terms of gene content, order, and function (Paterson et al., 1995(Paterson et al., , 2000Gale and Devos, 1998; Bennetzen, 2000). The bestdocumented cases of genome conservation are from the grass family (Poaceae), where rice (Oryza sativa) with its small genome has been selected as a nodal species to study the economically important cereal crops including corn (Zea mays), sorghum (Sorghum bicolor), wheat (Triticum aestivum), and barley (Hordeum vulgare;Devos and Gale, 2000). Extensive macrosynteny has also been observed within the Solanaceae (Tanksley et al., 1992), the Brassicaceae (Kowalski et al., 1994;Lagercrantz and Lydiate, 1996;Lagercrantz, 1998 In contrast to within-family comparisons, genome structure appears to be less conserved between distantly related species, where collinearity may only be apparent over small chromosomal intervals (Paterson et al., 1996(Paterson et al., , 2000. Paterson and colleagues have suggested that deciphering such relationships will require a very high density of genetic markers for comparison (Paterson et al., 2000). More recent analyses, however, reveal that plant genomes possess a dynamic microstructure (Ku et al., 2000;Vision et al., 2000) that may preclude establishing global relationships between distantly related plant species based on genetic map data alone. In lieu of whole-genome sequence data, an intermediate strategy involving complete sequencing and annotation of bacterial artificial chromosome (BAC)-size clones has been adopted by seve...
The retrograde transport of horseradish peroxidase (HRP), Golgi impregnations, and electron microscopic (EM) observations have been employed to investigate the intrinsic organization of one cytoarchitectonic subdivision of the feline dorsal column nuclei (DCN): the "clusters" region. Previous studies have demonstrated that neurons arranged i n typical cell clusters in the dorsal two-thirds of the feline DCN project to the ventrobasal complex (VB) of the thalamus. Following injections of HRP in the VB of adult cats, over 9WX of the neurons in this region contain detectable reaction product. These thalamic projecting neurons tTPNj a r e typically round, range from 20 to 35 ,urn in diameter, and have round nuclei and abundant cytoplasm.In Golgi preparations, TPN are identified by their characteristic arrangement in the cell clusters. Observations of their cytological characteristics in gold-toned preparations in both 1-pm-thick sections, and in thin sections at the EM level, supplement the data from HRP material. The dendrites of TPN in the clusters region characteristically converge in hhe perikarya-free center of each cluster, and appendages originate from both proximal and distal portions of the major dendrites of the,se neurons. These appendages vary in morphology from shortstalked, occasionally multi-lobed, bulbous thorns to long-stalked processes terminating in a single or multilobed swelling. Other appendages often display beaded swellings along their length (moniliform appendages).Neurons in the clusters region unlabelled by HRP injected in the VB have cytological characteristics quite distinct from those of TPN in the same region.Typically located at the periphery of the cell clusters, unlabelled neurons have fusiform perikai-ya, range in diameter from 8 to 12 p m along their short axis, and have highly indented nuclei and sparse cytoplasm. Tn Golgi preparations, small fusiform neurons located at the periphery of cell clusters typically have two major dendritic trunks originating from opposite poles of their perikarya.Observations in 1-pm-thick plastic sections of re-embedded Golgi-impregnated neurons of this t.ype support their identifications as neurons which are unlabelled after HRP injection in VB. Dendritic appendages are present also on this type of neuron, although they do not appear to be as frequent as i n the case of the TPN. Although the axon of the small, fusiform neurons have not been impregnated beyond the initial segment in the present Golgi material, thus precluding the classification of this type of neuron as a Golgi type I1 neuron, a combination of the HRP and Golgi observations suggest that these neurons are distinct from TPN, and are possibly interneurons.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.