A Meis family protein caudalizes neural cell fates in Xenopus

Abstract

A homologue of the Drosophila homothorax (hth) gene, Xenopus Meis3 (XMeis3), was cloned from Xenopus laevis. XMeis3 is expressed in a single stripe of cells in the early neural plate stage. By late neurula, the gene is expressed predominantly in rhombomeres two, three and four, and in the anterior spinal cord. Ectopic expression of RNA encoding XMeis3 protein causes anterior neural truncations with a concomitant expansion of hindbrain and spinal cord. Ectopic XMeis3 expression inhibits anterior neural induction in neuralized animal cap ectoderm explants without perturbing induction of pan-neural markers. In naive animal cap ectoderm, ectopic XMeis3 expression activates transcription of the posteriorly expressed neural markers, but not pan-neural markers. These results suggest that caudalizing proteins, such as XMeis3, can alter A-P patterning in the nervous system in the absence of neural induction. Regionally expressed proteins like XMeis3 could be required to overcome anterior signals and to specify posterior cell fates along the A-P axis.

Role of BMP-4 in the Inducing Ability of the Head Organizer in Xenopus laevis

“…tBR mRNA injected explants cultured alone expressed AG-1 and otx-2, as previously reported (Fig. 6E, lane 2) (Salzberg et al, 1999). In addition, tBR mRNA injected explants sandwiched between ectodermal explants did not express any marker gene (Fig.…”

Xmeis1, a protooncogene involved in specifying neural crest cell fate in Xenopus embryos

“…The expression pattern of both Xmeis1 and Xmeis3 were very similar in the tailbud stage where both transcripts were expressed in the hindbrain region, however, Xmeis3 expression ®rst appears at the mid-to late-gastrula stages and is not a maternal message. In contrast to the Xmeis1b-induced neural crest markers and pigmented cell masses in embryos, Xmeis3 over-expression shows no e ect on anterior or pan-neural marker expression in animal caps (Salzberg et al, 1999), and induces more posterior neural markers (HoxB9) as well as anterior truncations when over-expressed in embryos (Salzberg et al, 1999). These data suggest a distinct role for Xmeis1b in neural development.…”

“…Xmeis3 plays a role in neural tissue patterning in embryogenesis, especially, in the anteroposterior patterning of the neural axis (Salzberg et al, 1999). The expression pattern of both Xmeis1 and Xmeis3 were very similar in the tailbud stage where both transcripts were expressed in the hindbrain region, however, Xmeis3 expression ®rst appears at the mid-to late-gastrula stages and is not a maternal message.…”

“…Recently, a cDNA encoding Meis3, a Meis family member with 67% amino acid identity to Meis1, was isolated from Xenopus (Salzberg et al, 1999). Xmeis3 was expressed in the hindbrain and anterior spinal cord in the developing frog.…”

“…Xmeis3 was expressed in the hindbrain and anterior spinal cord in the developing frog. Ectopic expression in the developing embryo resulted in the caudalizing of neural tissue in the absence of neural induction, suggesting a role for this protein in anterior to posterior patterning in the nervous system (Salzberg et al, 1999).…”