20 research outputs found
Antigenic Stimuli do not Influence Thymic B Lymphocytes: A Morphological and Functional Study in Germ-Free and Conventionally Reared Piglets
We have recently reported that thymic B lymphocytes (TBL) are the first B-cell subpopulation
undergoing isotype switching to IgG and IgA during embryonic life. The aim of this study is to
analyze the influence of antigenic stimulation on TBL location and activity using a germ-free
(GF) newborn pig model, in which maternal antibodies and antigens do not affect B-cell
development. Immunohistological analysis showed that TBL were disseminated mainly in the
thymic medulla. There were no differences in the distribution of TBL, both in GF newborn
piglets before and after colonization with Escherichia coli and in older conventionally reared
(CONV) piglets. The number of immunoglobulin (Ig)-secreting cells measured by the ELISPOT
method was not influenced by microflora and food antigens. IgM-positive cells secreting IgM
and CD45RC-positive cells spontaneously producing IgM, IgG, and IgA were detected in
newborn thymus
The founder-cell transcriptome in the Arabidopsis apetala1 cauliflower inflorescence meristem
Light triggers PILS-dependent reduction in nuclear auxin signalling for growth transition
Local and systemic antibody response in infants after oral administration of inactivated enteropathogenicE. coli serotype O111 and O55
Cryptic variation in RNA-directed DNA-methylation controls lateral root development when auxin signalling is perturbed
Late seed maturation improves the preservation of seedling emergence during storage in soybean
JAGGED controls Arabidopsis petal growth and shape by interacting with a divergent polarity field
A flowering plant generates many different organs such as leaves, petals, and stamens, each with a particular function and shape. These types of organ are thought to represent variations on a common underlying developmental program. However, it is unclear how this program is modulated under different selective constraints to generate the diversity of forms observed. Here we address this problem by analysing the development of Arabidopsis petals and comparing the results to models of leaf development. We show that petal development involves a divergent polarity field with growth rates perpendicular to local polarity increasing towards the distal end of the petal. The hypothesis is supported by the observed pattern of clones induced at various stages of development and by analysis of polarity markers, which show a divergent pattern. We also show that JAGGED (JAG) has a key role in promoting distal enhancement of growth rates and influences the extent of the divergent polarity field. Furthermore, we reveal links between the polarity field and auxin function: auxin-responsive markers such as DR5 have a broader distribution along the distal petal margin, consistent with the broad distal organiser of polarity, and PETAL LOSS (PTL), which has been implicated in the control of auxin dynamics during petal initiation, is directly repressed by JAG. By comparing these results with those from studies on leaf development, we show how simple modifications of an underlying developmental system may generate distinct forms, providing flexibility for the evolution of different organ functions
Modeling Plant Tissue Growth and Cell Division
Morphogenesis is the creation of form, a complex process requiring the integration of genetics, mechanics, and geometry. Patterning processes driven by molecular regulatory and signaling networks interact with growth to create organ shape, often in unintuitive ways. Computer simulation modeling is becoming an increasingly important tool to aid our understanding of these complex interactions. In this chapter we introduce computational approaches for studying these processes on spatial, multicellular domains. For some problems, such as the exploration of many patterning processes, simulation can be done on static (non-growing) templates. These can range from abstract idealized cells, such as rectangular or hex grids, to more realistic shapes such as Voronoi regions, or even shapes extracted from bio-imaging data. More dynamic processes like phyllotaxis involve the interaction of growth and patterning, and require the simulation of growing domains. In the simplest case growth can be modeled descriptively, provided as an input to the model. Growth is specified globally, and must be designed carefully to avoid conflicts (growing cells must fit together). We present several methods for this that can be applied to shoots, roots, leaves, and other plant organs. However when shape is an emergent property of the model, different cells or areas of the tissue need to specify their growth locally, and physically-based methods (mechanics) are required to resolve conflicts. Among these are mass-spring, finite element, and Hamiltonian-based approaches