XB-ART-44568Dev Growth Differ December 1, 2011; 53 (9): 982-93.
Analyzing the function of a hox gene: an evolutionary approach.
We present an evolutionary approach to dissecting conserved developmental mechanisms. We reason that important mechanisms for making the bodyplan will act early, to generate the major features of the body and that they will be conserved in evolution across many metazoa, and thus, that they will be available in very different animals. This led to our specific approach of microarrays to screen for very early conserved developmental regulators in parallel in an insect, Drosophila and a vertebrate, Xenopus. We screened for the earliest conserved targets of the ectopically expressed hox gene Hoxc6/Antennapedia in both species and followed these targets up, using in situ hybridization, in the Xenopus system. The results indicate that relatively few of the early Hox target genes are conserved: these are mainly involved in the specification of the antero-posterior body axis and in gastrulation.
PubMed ID: 22150153
Article link: Dev Growth Differ
Genes referenced: anxa5 anxa9 ccng1 cdh1 cebpa cnn2 ctps1 dlx3 dlx5 dlx6 elavl3 exosc4 fezf2 foxn1 gbx2.2 gli3 herpud1 hes1 hes5.1 hes6.1 hesx1 hoxa9 hoxc6 hoxd1 id2 kctd15 kit krt12.4 krt7 lhx5 loc100036663 loc100496293 luc7l3 march8 mespa mig30 mpc2 msi1 mst1r msx1 ncoa6 nfe2 otx2 pabpc4 pax6 pisd-like.2 pkp3 plk2 prickle1 rab40b rasd1 rasl11b rpe65 sass6 sat1 shh sox7 sub1 tbxt.2 tmem184c tob1 tsc22d3 tuba1cl.3 vill vim vps26c znf703
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|Fig. 1. Drosophila Antennapedia and vertebrate Hox6 genes are considered to be orthologous. The figure below shows the single Drosophila Hox cluster (with its split indicated) and the four primary orthologous Hox clusters in a tetrapod vertebrate. The orthology of Antennapedia and the Hox6 genes is indicated by the same (light brown) color. Above are the axial domains of action of the different Hox genes. Indicated by different colors, in Drosophila (left) and a human fetus (right). Note that Antennapedia and Hox 6 genes have homolgous action domains (anterior thorax) in fly and human.|
|Fig. 2. The predicted Xl Hoxc6 and Antennapedia homeodomains show 91% sequence identity at the amino acid level. The figure shows homologous sequences in the two homeoproteins, indicated by colors. Red indicates homologous sequences within the homeodomain and hexapeptide. The other colors indicate homology in other parts of the homeoprotein. The labeling shows Antennapedia in Dorosophila melanogaster (ANTP DROMELA) and XlHbox1 (the oldname for Hoxc6) in Xenopus laevis (XlHbox1 XENLA).|
|Fig. 3. Functional homology between Xl Hoxc6 and Antennapedia. The figure shows: the phenotype obtained by overexpressing Antennapedia in Drosophila (above). Head segments are transformed to thorax, segment T2. Early XlHoxc6 ectopic expression in Drosophila gives the same phenotype as Antennapedia ectopic expression but Hoxa7 ectopic expression does not (not shown). The figure also shows the phenotype obtained by overexpressing XlHoxc6 in Xenopus (below). Head development is repressed and the thorax is enlarged.|
|Fig. 4 Heterochrony between Xenopus and Drosophila and plan of the experiment. The figure shows relative stages for ectopic hox expression, mRNA harvesting and gastrulation in Xenopus and Drosophila. Gb and Ge: beginning and end of gastrulation. Ho1, Ho6: the times when Hox1 and Hox6 expression start. Nb, Ne: the beginning and end of ectopic expression under the nullo promoter in Drosophila. Ha: time point for harvesting total mRNA. mRNA: injection of Xlhoxc6 mRNA into Xenopus. T = 0: start of development: zygote stage. The figure shows that the relationship between Hox expression and gastrulation is different in Xenopus (where Hox expression begins during gastrualtion) and Drosophila (where Hox expression begins before gastrulation). The latest time point for harvesting Drosophila mRNA (16 h: end of embryogenesis) is not shown (it is far right, off the figure).|
|Fig. 5. Numbers of Hoxc6 and Antennapedia targets. This figure shows numbers of targets at three developmental stages each in Drosophila and Xenopus and numbers of targets that overlap at different stages. Each disc represents targets obtained at a specific developmental stage, as indicated. Numbers of non-overlapping targets and numbers of overlapping targets (between stages) are as indicated. PS, probe sets. Top left: Upregulated targets in Drosophila. Top right: Downregulated targets in Drosophila. Bottom left: Upregulated targets in Xenopus. Bottom right: Downregulated targets in Xenopus.|
|Fig. 6. Confirmation of Xenopus conserved targets. Eight Xenopus targets were confirmed as being regulated by Hoxc6, as shown. In situ hybridizations of control embryos (left in each pair) and of embryos ectopically expressing Hoxc6 (right in each pair). We used probes detecting Xenopus probesets that are also conservedly regulated in Drosophila. These probes detected upregulation (all except Otx2) or downregulation (Otx2). Hoxc6 wild type expression is shown to indicate the normal Hoxc6 expression domain. Shown are stage 12 embryos from the vegetal side (most) or dorsal side (probes MGC82057, LOC495834, and Otx2). The name of each Xenopus target gene is at the top of the right hand picture in each pair.|
|ccng1 (cyclin G1) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 12, vegetal view, dorsal up.|
|herpud1 (homocysteine-inducible, endoplasmic reticulum stress-inducible, ubiquitin-like domain member 1) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 12, dorsal vegetal view, anterior up.|
|nfe2 (nuclear factor, erythroid 2) gene expression in Xenopus laevis embryo, assayed via in situ hybridization, NF stage 12, dorsal vegetal view, anterior up.|