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231.
The F-spondin genes are a family of extracellular matrix molecules united
by two conserved domains, FS1 and FS2, at the amino terminus plus a
variable number of thrombospondin repeats at the carboxy terminus.
Currently, characterized members include a single gene in Drosophila and
multiple genes in vertebrates. The vertebrate genes are expressed in the
midline of the developing embryo, primarily in the floor plate of the
neural tube. To investigate the evolution of chordate F-spondin genes, I
have used the basal position in chordate phylogeny of the acraniate
amphioxus. A single F-spondin-related gene, named AmphiF-spondin, was
isolated from amphioxus. Based on molecular phylogenetics, AmphiF-spondin
is closely related to a particular subgroup of vertebrate F-spondin genes
that encode six thrombospondin repeats. However, unlike these genes,
expression of AmphiF-spondin is not confined to the midline but is found
through most of the central nervous system. Additionally, AmphiF-spondin
has lost three thrombospondin repeats and gained two fibronectin type III
repeats, one of which has strong identity to a fibronectin type III repeat
from Deleted in Colorectal Cancer (DCC). Taken together, these results
suggest a complex evolutionary history for chordate F-spondin genes that
includes (1) domain loss, (2) domain gain by tandem duplication and
divergence of existing domains, and (3) gain of heterologous domains by
exon shuffling.
相似文献
232.
Dave VP Allman D Wiest DL Kappes DJ 《Journal of immunology (Baltimore, Md. : 1950)》1999,162(10):5764-5774
Thymic selection is controlled in part by the avidity of the interaction between thymocytes and APCs. In agreement, the selective outcome can be modulated by altering the expression levels of selecting ligands on APCs. Here we test the converse proposition, i. e., whether changing TCR levels on thymocytes can alter the selective outcome. To this end, we have generated mice in which all thymocytes express two transgenic TCRs simultaneously (dual TCR-expressing (DTE) mice), the class I-restricted HY TCR and the class II-restricted AND TCR. Due to mutual dilution, surface expression levels of the two individual transgenic TCRs are diminished in DTE relative to single TCR-expressing mice. We find that thymic selection is highly sensitive to these reductions in TCR surface expression. Positive selection mediated by the AND and HY TCRs is severely impaired or abolished, respectively. Negative selection of the HY TCR in male DTE mice is also partly blocked, leading to the appearance of significant numbers of double positive thymocytes. Also, in the periphery of male, but not female, DTE mice, substantial numbers of single positive CD8bright cells accumulate, which are positively selected in the thymus but by a highly inefficient hemopoietic cell-dependent process. Overall our results favor the interpretation that the outcome of thymic selection is not determined solely by avidity and the resulting signal intensity, but is also constrained by other factors such as the nature of the ligand and/or its presentation by different subsets of APCs. 相似文献
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236.
T. S. Sonstegard N. L. Lopez-Corrales S. M. Kappes R. T. Stone S. Ambady F. A. Ponce de Leon C. W. Beattie 《Mammalian genome》1997,8(1):16-20
Genotypic data for 56 microsatellites (ms) generated from maternal full sib families nested within paternal half sib pedigrees
were used to construct a linkage map of the bovine X Chromosome (Chr) (BTX) that spans 150 cM (ave. interval 2.7 cM). The
linkage map contains 36 previously unlinked ms; seven generated from a BTXp library. Genotypic data from these 36 ms was merged
into an existing linkage map to more than double the number of informative BTX markers. A male specific linkage map of the
pseudoautosomal region was also constructed from five ms at the distal end of BTXq. Four informative probes physically assigned
by fluorescence in situ hybridization defined the extent of coverage, confirmed the position of the pseudoautosomal region
on the q-arm, and identified a 4.1-cM marker interval containing the centromere of BTX.
Received: 14 July 1996 / Accepted: 19 September 1996 相似文献
237.
Tad S. Sonstegard Nestor L. Lopez-Corrales Steven M. Kappes Craig W. Beattie Timothy P.L. Smith 《Mammalian genome》1997,8(10):751-755
The ``double-muscling' (mh) locus has been localized to an interval between the centromere and the microsatellite marker TGLA44 on bovine Chromosome (Chr) 2 (BTA2). We identified segments of conserved synteny that correspond to this region of BTA2 by
assigning large genomic clones containing bovine homologs of seven genes from the long arm of human Chr 2 (HSA2q). Polymorphic
markers developed from these clones integrated the physical and linkage maps of BTA2 from 2q12 to 2q44 and extended genetic
coverage towards the centromere. This comparative analysis suggests the mh locus resides on HSA2q near both the protein C and collagen type III alpha-1 genes. Overall, our data reveal a complex rearrangement
of gene order between BTA2q12-44 and HSA2q14-37 that underscores the need to establish boundaries of conserved synteny when
applying comparative mapping information to identify genes or traits of interest.
Received: 3 March 1997 / Accepted: 12 May 1997 相似文献
238.
G. A. Hawkins S. Solinas Toldo M. D. Bishop S. M. Kappes R. Fries Craig W. Beattie 《Mammalian genome》1995,6(4):249-254
We have initiated a mapping strategy using cosmid clones to chromosomally anchor a high-resolution bovine genetic linkage map. Ten cosmids containing microsatellites were assigned to bovine chromosomes by fluorescence in situ suppression hybridization (FISH). Four cosmid clones, three of which contain an informative microsatellite, were assigned to autosomes 5, 13, 24, and 28. The assignment to autosome 13 anchors bovine syntenic group U11. Two additional cosmid clones, each containing informative microsatellites, are assigned to autosomes 9 and 29, auchoring bovine linkage groups U2 and U8, respectively. Four cosmid clones, three of which contain informative microsatellites, also provide the first assignment to autosome 25, anchoring bovine syntenic group U7 and orienting the corresponding linkage group relative to the centromere. 相似文献
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