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Dev Dyn
2006 Apr 01;2354:949-57. doi: 10.1002/dvdy.20713.
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Vertebrate Rel proteins exhibit Dorsal-like activities in early Drosophila embryogenesis.
Prothmann C
,
Armstrong NJ
,
Roth S
,
Rupp RA
.
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In Drosophila, the Toll/Dorsal pathway triggers the nuclear entry of the Rel protein Dorsal, which controls dorsoventral patterning in early embryogenesis and plays an important role in innate immunity of the adult fly. In vertebrates, the homologous Toll/IL-1 receptor signaling pathway directs the nuclear localization of Rel/NF-kappaB complexes, which activate genes involved in proliferation, apoptosis, and immune response. Recently, first evidence has been reported for the activity of vertebrate Rel proteins and a Toll-like signaling pathway in the dorsoventral patterning process of Xenopus laevis embryos. Given the evolutionary divergence of the fly and frog model organisms, these findings raise the question, to what extent the effector functions of this pathway have been conserved? Here, we report the ability of two Xenopus Rel proteins to partially substitute for several, but not all, functions of the Dorsal protein in Drosophila embryos. Our results suggest the interaction between Rel proteins and their cytoplasmic inhibitors as an important interface of evolutionary adaptation.
Figure 4. Injections of Xenopus Xrels mRNA into dl-/- embryos alter the expression of zygotic target genes of Dorsal protein. Whole-mount RNA in situ hybridizations and immunological staining reactions were carried out with probes for the indicated RNA probes, or Twi antibody, as indicated to the left. Embryos at the cellular blastoderm stage were oriented with anterior to the left and dorsal side up. Columns from left to right: Wild-type embryos, dorsalized dlH/Df(2L)TW119 embryos, Xenopus Xrel1 mRNA (0.25 mu g/ mu l) -injected dlH/Df(2L)TW119 embryos and Xenopus Xrel2 mRNA (0.05 mu g/ mu l) -injected dlH/Df(2L)TW119 embryos. Probes/antibody: first row: dpp. Dorsal expression in wild-type embryos and overall expression in dlH/Df(2L)TW119 embryos. Xrel1- and -2-injected dlH/Df(2L)TW119 embryos show significantly reduced expression of dpp in the central region of the embryo where the injection occurred. Second row: sog. Ventral expression in wild-type embryos and no expression in dlH/Df(2L)TW119 embryos. Xrel1- and -2-injected dlH/Df(2L)TW119 embryos exhibit high expression of sog. Third row: Twist. Ventral expression of Twist protein in wild-type embryos and no expression in dlH/Df(2L)TW119 embryos. In Xrel1- and -2-injected dlH/Df(2L)TW119 embryos, Twist protein can be detected around the dorsoventral (DV) circumference in a distinct area near the injection site where the highest concentrations the Xrel mRNAs were likely to be. Fourth row: sna. Ventral expression in wild-type embryos, no expression in dlH/Df(2L)TW119 and Xrel1-injected dlH/Df(2L)TW119 embryos. Xrel2-injected dlH/Df(2L)TW119 embryos show faint sna expression close to the injection site. Fifth row: rho. Rhomboid exhibits its complex expression pattern in wild-type embryos by showing an anterior ldquo head rdquo stripe, a dpp-dependent dorsally located and a dorsal-dependent ventral expression domain. In dlH/Df(2L)TW119 embryos, the ventral expression domain disappears and the two dorsal ones spread circumferentially around the DV axis of the embryo. In Xrel1- and -2-injected dlH/Df(2L)TW119 embryos, the dpp-dependent dorsal expression of rho is almost ablated, but its ventral expression domain is not restored.
