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The mouse Hox 2.1 gene contains a homeobox sequence and is therefore a candidate for a vertebrate gene involved in the control of embryonic patterning or positional specification. To investigate this possibility, we have used in situ hybridization to determine the pattern of Hox 2.1 expression during mouse embryogenesis. At 8.5 days post coitum, Hox 2.1 is expressed at a low level in the posterior neuroectoderm and mesoderm, and in the neuroectoderm of the presumptive hindbrain. At 12.5 days p.c., Hox 2.1 is expressed in an anteroposterior restricted domain extending from the hindbrain throughout the length of the spinal cord, predominantly in the dorsal region. Between 12.5 and 13.5 days p.c. the domain becomes localized to the occipital and cervical regions. We also detect Hox 2.1 RNA in the embryonic lung, stomach, mesonephros and metanephros, as well as in myenteric plexus, dorsal root ganglia and the nodose ganglion, and in mature granulocytes. The embryonic expression of Hox 2.1 in neural tissue is compared with that of Hox 3.1, which also shows anteroposterior restricted domains of gene expression. These patterns of expression are not clearly consistent with Hox 2.1 or Hox 3.1 having roles in segmental patterning. However, the data are consistent with these genes having regulatory roles in anteroposterior positional specification in the neuroectoderm and mesoderm, and suggest that Hox 2.1 may also have functions during organogenesis.  相似文献   

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Mouse embryos were exposed to maternally administered RA on day 8.0 or day 7 3/4 of development, i.e. at or just before the differentiation of the cranial neural plate, and before the start of segmentation. On day 9.0, the RA-treated embryos had a shorter preotic hindbrain than the controls and clear rhombomeric segmentation was absent. These morphological effects were correlated with alterations in the spatiotemporal distribution patterns of two genes, Hox-2.9 and Krox-20, which are expressed in the otic and preotic hindbrain and in specific neural crest cell populations. Hox-2.9 was expressed throughout the preotic hindbrain region, instead of being confined to rhombomere 4. Krox-20 was not expressed rostral to the Hox-2.9 domain, i.e. its normal rhombomere 3 domain was absent. The Hox-2.9/Krox-20 boundary was ill-defined, with patches of alternating expression of the two genes. In migrating neural crest cells, Hox-2.9 expression was both abnormally extensive and abnormally prolonged. Neural crest cells expressing Krox-20 remained close to the neural tube. Embryos exposed to RA on day 8 1/4 appeared to be morphologically normal. We suggest that early events leading to rhombomeric segmentation and rhombomere-specific gene expression are specifically vulnerable to raised RA levels, and may require RA levels lower than those in the region of somitic segmentation.  相似文献   

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The sequence of a mouse Hox 2.9 cDNA clone is presented. The predicted homeodomain is similar to that of the Drosophila gene labial showing 80% identity. The equivalent gene in the Hox 1 cluster is Hox 1.6 which shows extensive similarity to Hox 2.9 both within and outside the homeodomain. Hox 2.9 and Hox 1.6 are the only two mouse members of the labial-like family of homeobox-containing genes as yet identified. Hox 2.9 has previously been shown to be expressed in a single segmental unit of the developing hindbrain (rhombomere) and has been predicted to be involved in conferring rhombomere identity. To analyse further the function of Hox 2.9 during development and to determine if the other mouse labial-like gene Hox 1.6, displays similar properties, we have investigated the expression patterns of these two genes and an additional rhombomere-specific gene, Krox 20, on consecutive embryonic sections at closely staged intervals. This detailed analysis has enabled us to draw the following conclusions: (1) There are extensive similarities in the temporal and spatial expression of Hox 2.9 and Hox 1.6, throughout the period that both genes are expressed in the embryo (7 1/2 to 10 days). At 8 days the genes occupy identical domains in the neuroectoderm and mesoderm with the same sharp anterior boundary in the presumptive hindbrain. These similarities indicate a functional relationship between the genes and further suggest that the labial-like genes are responding to similar signals in the embryo. (2) By 9 days the neuroectoderm expression of both genes retreats posteriorly along the anteroposterior (AP) axis. The difference at this stage between the expression patterns is the persistence of Hox 2.9 in a specific region of the hindbrain, illustrating the capacity of Hox 2.9 to respond to additional positional regulatory signals and indicating a unique function for this gene in the hindbrain. (3) The restriction of Hox 2.9 expression in the hindbrain occurs at 8 1/2 days, approximately the same time as Krox 20 is first detected in the posterior adjoining domain. The mutually exclusive expression of Hox 2.9 and Krox 20 demarcated by sharp expression boundaries suggest that compartmentalisation of cells within the hindbrain has occurred up to 6 h before rhombomeres (morphological segments) are clearly visible. (4) Hox 2.9 expression is confined to the region of rhombomere 4 that shows cell lineage restriction and, unlike Krox 20, is expressed throughout the period that rhombomeres are visible (to 11 1/2 days).(ABSTRACT TRUNCATED AT 400 WORDS)  相似文献   

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An early developmental phase of pp60c-src expression in the neural ectoderm   总被引:10,自引:0,他引:10  
The expression of the normal cellular src protein (pp60c-src) was investigated in the early chick embryo during gastrulation and neurulation by immunoperoxidase staining using antisera, raised against bacterially expressed pp60v-src, that recognizes pp60c-src specifically in normal cells. During gastrulation pp60c-src immunoreactivity appeared primarily in the neural ectoderm and was much less prominent in the mesoderm, endoderm, and nonneural ectoderm. During neurulation pp60c-src immunoreactivity began to disappear from the wall of the closing neural tube so that by the completion of neural tube closure no specific pp60c-src immunoreactivity appeared in any of the neuroepithelial cells composing the neural tube. These studies reveal a developmental phase of pp60c-src expression even earlier than reported previously, when neuroepithelial cells of later embryos undergo terminal neuronal differentiation. These findings raise the possibility that pp60c-src may mediate two different differentiation signals in the neuronal lineage.  相似文献   

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The dorsal ectoderm of vertebrate gastrula is first specified into anterior fate by an activation signal and posteriorized by a graded transforming signal, leading to the formation of forebrain, midbrain, hindbrain and spinal cord along the anteroposterior (A-P) axis. Transplanted non-axial mesoderm rather than axial mesoderm has an ability to transform prospective anterior neural tissue into more posterior fates in zebrafish. Wnt8 is a secreted factor that is expressed in non-axial mesoderm. To investigate whether Wnt8 is the neural posteriorizing factor that acts upon neuroectoderm, we first assigned Frizzled 8c and Frizzled 9 to be functional receptors for Wnt8. We then, transplanted non-axial mesoderm into the embryos in which Wnt8 signaling is cell-autonomously blocked by the dominant-negative form of Wnt8 receptors. Non-axial mesodermal transplants in embryos in which Wnt8 signaling is cell-autonomously blocked induced the posterior neural markers as efficiently as in wild-type embryos, suggesting that Wnt8 signaling is not required in neuroectoderm for posteriorization by non-axial mesoderm. Furthermore, Wnt8 signaling, detected by nuclear localization of beta-catenin, was not activated in the posterior neuroectoderm but confined in marginal non-axial mesoderm. Finally, ubiquitous over-expression of Wnt8 does not expand neural ectoderm of posterior character in the absence of mesoderm or Nodal-dependent co-factors. We thus conclude that other factors from non-axial mesoderm may be required for patterning neuroectoderm along the A-P axis.  相似文献   

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Chick Ghox 2.9 protein, a homeodomain-containing polypeptide, is first detected in the mid-gastrula stage embryo and its levels increase rapidly in the late gastrula. At this time, the initially narrow band of expression along the primitive streak expands laterally to form a shield-like domain that encompasses almost the entire posterior region of the embryo and extends anteriorly as far as Hensen's node. We have found that this expression domain co-localizes with a morphological feature that consists of a stratum of refractile, thickened mesoderm. Antibody-staining indicates that Ghox 2.9 protein is present in all cells of this mesodermal region. In contrast, expression within the ectoderm overlying the region of refractile mesoderm varies considerably. The highest levels of expression are found in ectoderm near the streak and surrounding Hensen's node, regions that recent fate mapping studies suggest that primarily destined to give rise to neurectoderm. At the definitive streak stage (Hamburger and Hamilton stage 4) the chick embryo is especially sensitive to the induction of axial malformations by retinoic acid. Four hours after the treatment of definitive streak embryos with a pulse of retinoic acid the expression of Ghox 2.9 protein is greatly elevated. This ectopic expression occurs in tissues anterior to Hensen's node, including floor plate, notochord, presumptive neural plate and lateral plate mesoderm, but does not occur in the anteriormost region of the embryo. The ectopic induction of Ghox 2.9 is strongest in ectoderm, and weaker in the underlying mesoderm. Endoderm throughout the embryo is unresponsive. At stage 11, Ghox 2.9 is normally expressed at high levels within rhombomere 4 of the developing hindbrain. In retinoic-acid-treated embryos which have developed to this stage, typical rhombomere boundaries are largely absent. Nevertheless, Ghox 2.9 is still expressed as a discrete band, but one that is widened and displaced to a more anterior position.  相似文献   

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The Hox genes are a class of putative developmental control genes that are thought to be involved in the specification of positional identity along the anteroposterior axis of the vertebrate embryo. It is apparent from their expression pattern that their regulation is dependent upon positional information. In a previous analysis of the Hox-1.1 promoter in transgenic mice, we identified sequences that were sufficient to establish transgene expression in a specific region of the embryo. The construct used, however, did not contain enough regulatory sequences to reproduce all aspects of Hox-1.1 expression. In particular, neither a posterior boundary nor a restriction of expression to prevertebrae was achieved. Here we show correct regulation by Hox-1.1 sequences in transgenic mice and identify the elements responsible for different levels of control. Concomitant with the subdivision of mesodermal cells into different lineages during gastrulation and organogenesis, Hox-1.1 expression is restricted to successively smaller sets of cells. Distinct elements are required at different stages of development to execute this developmental programme. One position-responsive element (130 bp nontranslated leader) was shown to be crucial for the restriction of expression not only along the anteroposterior axis of the embryo, setting the posterior border, but also along the dorsoventral axis of the neural tube and to the lineage giving rise to the prevertebrae. Thus, Hox-1.1 expression is established in a specific region of the embryo and in a specific lineage of the mesoderm by restricting the activity of the promoter by the combined effect of several regulatory elements.  相似文献   

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