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Genomic and cDNA clones of an Msx class homeobox gene were isolated from amphioxus (Branchiostoma floridae). The gene, AmphiMsx, is expressed in the neural plate from late gastrulation; in later embryos it is expressed in dorsal cells of the neural
tube, excluding anterior and posterior regions, in an irregular reiterated pattern. There is transient expression in dorsal
cells within somites, reminiscent of migrating neural crest cells of vertebrates. In larvae, mRNA is detected in two patches
of anterior ectoderm proposed to be placodes. Evolutionary analyses show there is little phylogenetic information in Msx protein
sequences; however, it is likely that duplication of Msx genes occurred in the vertebrate lineage.
Received: 12 October 1998 / Accepted: 26 December 1998 相似文献
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Shi-cui Zhang Nicholas D. Holland L. Z. Holland 《Development genes and evolution》1997,206(8):532-535
In amphioxus embryos, the nascent and early mesoderm (including chorda-mesoderm) was visualized by expression of a Brachyury gene (AmBra-2). A band of mesoderm is first detected encircling the earliest (vegetal plate stage) gastrula sub-equatorially. Soon thereafter,
the vegetal plate invaginates, resulting in a cap-shaped gastrula with the mesoderm localized at the blastoporal lip and completely
encircling the blastopore. As the gastrula stage progresses, DiI (a vital dye) labeling demonstrates that the entire mesoderm
is internalized by a slight involution of the epiblast into the hypoblast all around the perimeter of the blastopore. Subsequently,
during the early neurula stage, the internalized mesoderm undergoes anterior extension mid-dorsally (as notochord) and dorsolaterally
(in paraxial regions where segments will later form). By the late neurula stage, AmBra-2 is no longer transcribed throughout the mesoderm as a whole; instead, expression is detectable only in the posterior mesoderm
and in the notochord, but not in paraxial mesoderm where definitive somites have formed.
Received: 28 November 1996 / Accepted: 2 January 1997 相似文献
5.
Julie E. Cooke Qiling Xu Stephen W. Wilson N. Holder 《Development genes and evolution》1997,206(8):515-531
Eph-related receptor tyrosine kinases (RTKs) are the largest known subfamily of RTKs, comprising at least a dozen members. Expression
studies suggest roles for these genes in patterning and differentiation of the nervous system, the neural crest, developing
limbs and somites. Some of the recently isolated family of ligands for Eph-related RTKs have been shown to function as positional identifiers in the retinotectal system. We have previously characterised
three Eph-related RTKs in the zebrafish (rtk1-3). Here we report the identification of five new zebrafish Eph-related RTKs (rtk4, rtk5, rtk6, rtk7 and rtk8) and describe their dynamic expression patterns. Based on these expression patterns, we propose that rtk4-8 play various roles in establishing territories within the developing central nervous system (CNS) and in the subsequent differentiation
of defined neuronal populations.
Received: 22 November 1996 / Accepted: 3 January 1997 相似文献
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The embryonic development of amphioxus (cephalochordates) has much in common with that of vertebrates, suggesting a close
phylogenetic relationship between the two chordate groups. To gain insight into alterations in the genetic cascade that accompanied
the evolution of vertebrate embryogenesis, we investigated the formation of the chordamesoderm in amphioxus embryos using
the genes Brachyury and fork head/HNF-3 as probes. Am(Bb)Bra1 and Am(Bb)Bra2 are homologues of the mouse Brachyury gene isolated from Branchiostoma belcheri. Molecular phylogenetic analysis suggests that the genes are independently duplicated in the amphioxus lineage. Both genes
are initially expressed in the involuting mesoderm of the gastrula, then in the differentiating somites of neurulae, followed
by the differentiating notochord and finally in the tail bud of ten-somite stage embryos. On the other hand, Am(Bb)fkh/HNF3-1, an amphioxus (B. belcheri) homologue of the fork head/HNF-3 gene, is initially expressed in the invaginating endoderm and mesoderm, then later in the differentiating notochord and in
the tail bud. With respect to these two types of genes, the formation of the notochord and tail bud in amphioxus embryos shows
similarity and dissimilarity with that of the notochord and tail bud in vertebrate embryos.
Received: 21 November 1996 / Accepted: 24 January 1997 相似文献
7.
An amphioxus netrin gene is expressed in midline structures during embryonic and larval development 总被引:1,自引:0,他引:1
Shimeld S 《Development genes and evolution》2000,210(7):337-344
Members of the netrin gene family have been identified in vertebrates, Drosophila and Caenorhabditis elegans and found to encode secreted molecules involved in axon guidance. Here I use the conserved function of netrins in triploblasts,
coupled with the phylogenetic position of amphioxus (the closest living relative of the vertebrates), to investigate the evolution
of an axon guidance cue in chordates. A single amphioxus netrin gene was isolated by PCR and cDNA library screening and named
AmphiNetrin. The predicted AmphiNetrin protein showed high identity to other netrin family members but differed in that the third of three EGF repeats found in
other netrins was absent. Molecular phylogene-tic analysis showed that despite the absent EGF repeat AmphiNetrin is most closely related to the vertebrate netrins. AmphiNetrin expression was identified in embryonic notochord and floor plate, a pattern similar to that of vertebrate netrin-1 expression. AmphiNetrin expression was also identified more widely in the posterior larval brain, and in the anterior extension of the notochord
that underlies the anterior of the amphioxus brain. All of these areas of expression are correlated with developing axon trajectories:
The floor plate with ventrally projecting somatic motor neurons and Rohde cell projections, the posterior brain with the ventral
commissure and primary motor centre and the anterior extension of the notochord with ventrally projecting neurons associated
with the median eye. Amphioxus is naturally cyclopaedic and also lacks the ventral brain cells that the induction of which
results in the splitting of the vertebrate eye field and, when missing, result in cyclopaedia. These cells normally express
netrins required for developing axon tracts in the brain, and the expression of AmphiNetrin in the anterior extension of the notochord underlying the brain may explain how amphioxus is able to maintain ventral guidance
cues while lacking these cells.
Received: 15 November 1999 / Accepted: 27 January 2000 相似文献
8.
The evolution of the hedgehog gene family in chordates: insights from amphioxus hedgehog 总被引:9,自引:0,他引:9
Sebastian M. Shimeld 《Development genes and evolution》1999,209(1):40-47
The hedgehog family of intercellular signalling molecules have essential functions in patterning both Drosophila and vertebrate embryos. Drosophila has a single hedgehog gene, while vertebrates have evolved at least three types of hedgehog genes (the Sonic, Desert and
Indian types) by duplication and divergence of a single ancestral gene. Vertebrate Sonic-type genes typically show conserved
expression in the notochord and floor plate, while Desert- and Indian-type genes have different patterns of expression in
vertebrates from different classes. To determine the ancestral role of hedgehog in vertebrates, I have characterised the hedgehog
gene family in amphioxus. Amphioxus is the closest living relative of the vertebrates and develops a similar body plan, including
a dorsal neural tube and notochord. A single amphioxus hedgehog gene, AmphiHh, was identified and is probably the only hedgehog family member in amphioxus, showing the duplication of hedgehog genes to
be specific to the vertebrate lineage. AmphiHh expression was detected in the notochord and ventral neural tube, tissues that express Sonic-type genes in vertebrates. This
shows that amphioxus probably patterns its ventral neural tube using a molecular pathway conserved with vertebrates. AmphiHh was also expressed on the left side of the pharyngeal endoderm, reminiscent of the left-sided expression of Sonic hedgehog in chick embryos which forms part of a pathway controlling left/right asymmetric development. These data show that notochord,
floor plate and possibly left/right asymmetric expression are ancestral sites of hedgehog expression in vertebrates and amphioxus.
In vertebrates, all these features have been retained by Sonic-type genes. This may have freed Desert-type and Indian-type
hedgehog genes from selective constraint, allowing them to diverge and take on new roles in different vertebrate taxa.
Received: 20 July 1998 / Accepted: 23 September 1998 相似文献
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Competence for cell fate determination and cellular differentiation is under tight control of regulatory genes. Yan, a nuclear
target of receptor tyrosine kinase (RTK) signaling, is an E twenty six (ETS) DNA-binding protein that functions as a negative
regulator of cell differentiation and proliferation in Drosophila. Most members of RTK signaling pathways are highly conserved through evolution, yet no yan orthologues have been identified to date in vertebrates. To investigate the degree of yan conservation during evolution, we have characterized a yan homologue from a sibling species of D. melanogaster, D. virilis. Our results show that the organization, primary structure and expression pattern of yan are highly conserved. Both genes span over 20 kb and contain four exons with introns at identical positions. The areas with
highest amino acid similarity include the Pointed and ETS domain but there are other discrete regions with a high degree of
similarity. Phylogenetic analysis reveals that yan’s closest relative is the human tel gene, a negative regulator of differentiation in hematopoetic precursors. In both species, Yan is dynamically expressed beginning
as early as stage 4/5 and persisting throughout embryogenesis. In third instar larvae, Yan is expressed in and behind the
morphogenetic furrow of the eye imaginal disc as well as in the laminar precursor cells of the brain. Ovarian follicle cells
also contain Yan protein. Conservation of the structure and expression patterns of yan genes strongly suggests that regulatory mechanisms for their expression are also conserved in these two species.
Received: 3 November 1998 / Accepted: 9 December 1998 相似文献
11.
An increasing number of genes are known to show expression in the cranial neural crest area. So far it is very difficult to
analyze their effect on neural crest cell migration because of the lack of transplantation techniques. This paper presents
a simple method to study the migratory behavior of cranial neural crest cells by homo- and heterotopic transplantations: Green
fluorescent protein (GFP) RNA was injected into one blastomere of Xenopus laevis embryos at the 2-cell stage. The cranial neural crest area of stage 14 embryos was transplanted into the head or trunk region
of an uninjected host embryo, and the migration was monitored by GFP fluorescence. The transplants were further examined by
double immunostaining and confocal microscopy to trace migratory routes inside the embryo, and to exclude contaminations of
grafts with foreign tissues. Our results demonstrate that we developed a highly efficient and reproducible technique to study
the migratory ability of cranial neural crest cells. It offers the possibility to analyze genes involved in neural crest cell
migration by coinjecting their RNA with that of GFP.
Received: 28 September 1999 / Accepted: 17 November 1999 相似文献
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R. E. Steele Pauline Lieu Ninh H. Mai M. Andrew Shenk Michael P. Sarras Jr. 《Development genes and evolution》1996,206(4):247-259
A gene encoding a receptor protein-tyrosine kinase closely related to the vertebrate insulin receptor has been identified
in the Cnidarian Hydra vulgaris. The gene is expressed in both epithelial layers of the adult polyp. A particularly high level of expression is seen in the
ectoderm of the proximal portions of the tentacles and in a ring of ectodermal cells at the border between the foot basal
disk and body column. The expression pattern of the gene in asexual buds is dynamic; expression is high throughout the newly
emerging bud but the area of high expression becomes restricted to the apex as the bud lengthens. When the bud begins hypostome
and tentacle formation, a high level of expression appears at the bases of the emerging tentacles. Finally, a ring of high
expression appears just above the foot of the bud, completing the pattern seen in the adult polyp. The presence of this receptor
and its pattern of expression suggested that an endogenous molecule related to insulin plays a role in regulating cell division
in the body column and in differentiation of the tentacle and foot cells in Hydra, with the switch between the two being determined by the level of the receptor. Treatment of Hydra polyps with mammalian insulin caused an increase in the number of ectodermal and endodermal cells undergoing DNA synthesis.
Received: 19 April 1996 / Accepted: 5 July 1996 相似文献
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Summary. The lancelet (amphioxus), a cephalochordate, is the closest invertebrate relative to vertebrates, with a simple vertebrate-like
body plan and a prototypical genome. We have determined D-aspartic acid (D-Asp) and major free L-amino acids (L-AAs) content
in the nervous system (neural tube) of the European amphioxus Branchiostoma lanceolatum, and have compared these values with those of molluscs and human brain. The B. lanceolatum neural tube contains relatively high amounts of L-Glu, L-Asp, L-Ala and L-Gly. Thus, the amphioxus neural tube has in common
with the molluscan and human nervous systems the presence of appreciable amounts of L-Glu and L-Asp, which suggests that they
are the most common neurotransmitters among these phylogenetically distant animal groups. The relatively high concentration
of L-Ala in amphioxus is consistent with that found in molluscs and the low concentration of taurine is consistent with that
described in the human brain.
The D-Asp concentration, very high in the molluscan nervous system, was rather low in amphioxus, although a little higher
than the extremely low amounts observed in the human brain. Our data on free amino acids composition is in agreement with
the intermediate phylogenetic position of cephalochordates, in terms of the evolutionary transition from simple to complex
neural systems. 相似文献
16.
We have isolated the Drosophila gene skittles (sktl) which shows homology to members of a novel family of phosphatidylinositol-4-phosphate 5-kinases, including the gene product
encoded by the human STM-7.I gene which has been assigned to the neurodegenerative disorder Friedreichs ataxia. In situ hybridization
reveals sktl expression during oogenesis and spermatogenesis.
Received: 7 February1997 / Accepted: 4 April 1997 相似文献
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Vertebrate non-retinal pigment cells are derived from neural crest (NC) cells, and several mutations have been identified
in the Mexican axolotl Ambystoma mexicanum (Ambystomatidae) that affect the development of these cell lineages. In ”white” (d) mutant axolotls, premigratory NC cells differentiate as pigment cells, yet fail to disperse, survive, or both, and this
leads to a nearly complete absence of pigment cells in the skin. Previous studies revealed that d affects pigment cell development non-autonomously, and have reported differences between white and wild-type axolotls in
the structure and composition of the extracellular matrix through which NC and pigment cells migrate. Here we test the correspondence
of d and two candidate genes: steel and AxPG. In amniotes, Steel encodes the cytokine Steel factor (mast cell growth factor; stem cell factor; kit ligand), which is expressed along the migratory
pathways of melanocyte precursors and is required by these cells for their migration and survival; mammalian Steel mutants resemble white mutant axolotls in having a deficit or complete absence of pigment cells. In contrast, AxPG encodes aPG-M/versican-like proteoglycan that may promote the migration of A. mexicanum pigment cells, and AxPGexpression is reduced in white mutant axolotls. We cloned a salamander orthologue of steel and used a partial genetic linkage map of Ambystoma to determine the genomic locations of steel, AxPG, and d. We show that the three genes map to different linkage groups, excluding steel and AxPG as candidates for d.
Received: 11 November 1998 / Accepted: 30 January 1999 相似文献
19.
In vertebrate embryogenesis, many Wnt genes are expressed in the neural tube and play important roles in regional specifications. There are many subfamilies of Wnt, and each subfamily shows distinct expression patterns in the neural tube. Ascidian larvae have a dorsal hollow neural tube
similar to that of vertebrates. To date, the degree of correspondence between regionality of the neural tubes of ascidians
and vertebrates remains unclear. To compare cellular differences in neural tubes, Wnt genes can be used as molecular probes. We report here that a new member of the ascidian Wnt gene family, HrWnt-7, was expressed in the tail neural tube at the early tailbud stage. Moreover, in cross-section, HrWnt-7 was expressed in the dorsal and ventral ependymal cells.
Received: 14 July 2000 / Accepted: 1 August 2000 相似文献
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Ultrastructural and tissue-culture studies on the role of fibronectin,collagen and glycosaminoglycans in the migration of neural crest cells in the fowl embryo 总被引:12,自引:0,他引:12
D. F. Newgreen I. L. Gibbins J. Sauter B. Wallenfels R. Wütz 《Cell and tissue research》1982,221(3):521-549
Summary The initial migration of neural crest (NC) cells into cell-free space was studied by transmission electron microscopy at trunk levels of fowl embryos, some of which were fixed in the presence of ruthenium red. Migrating NC cells occurred in zones which contained fewer ruthenium-red stained 15–40 nm diameter granules than other regions. The ruthenium-red stained granules were linked by similarly stained thin ( 3 nm diameter) microfibrils. The granules resemble proteoglycan and the microfibrils may be hyaluronate. NC cells contacted thicker ( 10 nm diameter) fibrils and interstitial bodies, which did not require ruthenium red for visualization. Cytoplasmic microfilaments were sometimes aligned at the point of contact with the extracellular fibrils, which may be fibronectin and collagen.Phase-contrast time-lapse videotaping and scanning electron microscopy showed that NC cells of the fowl embryo in vitro migrated earlier and more extensively on glass coated with fibronectin-rich fibrous material and adsorbed fibronectin molecules than on glass coated with collagen type I (fibres and adsorbed molecules). NC cells became completely enmeshed in fibronectin-rich fibres, but generally remained on the surface of collagen-fibre gels. When given a choice, NC cells strongly preferred fibronectin coatings to plain glass, and plain glass to dried collagen gels. NC cells showed a slight preference for plain glass over glass to which collagen was adsorbed. Addition to the culture medium of hyaluronate (initial conc. 20 mg/ml), chondroitin (5 mg/ml) and fully sulphated chondroitin sulphate and dermatan sulphate (up to 10 mg/ml) did not drastically alter NC cell migration on fibronectin-rich fibrous substrates. However, partially desulphated chondroitin sulphate (5mg/ml) strongly retarded the migration of NC cells.The in vivo and in vitro studies suggest that fibronectin may dictate the pathways of NC cell migration by acting as a highly preferred physical substrate. However, the utilization of these pathways may be reduced by the presence of proteoglycans bearing undersulphated chondroitin sulphate.Abbreviations
NC
neural crest
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ECM
extracellular material
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GAG
glycosaminoglycan
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FN
fibronectin
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CIG
cold insoluble globulin
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TEM
transmission electron microscopy
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SEM
scanning electron microscopy
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DMEM-H HEPES
buffered Dulbecco's modified Eagle's medium
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FCS
foetal calf serum
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CEE
chick embryo extract
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SDS-PAGE
sodium dodecyl sulphate-polyacrylamide gel electrophoresis
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PBS
phosphate-buffered saline 相似文献