Developmental expression of Xenopus fragile X mental retardation-1 gene.
Dysregulation of Fragile X mental retardation-1 (Fmr1) gene expression results in an inherited form of mental retardation known as the Fragile X syndrome (FXS). Fmr1 is a highly conserved gene with a broad yet distinctive expression pattern during vertebrate development. Here, we examined the expression pattern of Fmr1 during Xenopus embryonic development. Zygotic expression of Fmr1 began just prior to gastrulation and gradually increased during subsequent embryonic stages. By in situ hybridization, Fmr1 transcripts were detected by early tailbud stage and showed robust expression in the central nervous system (CNS), eye and pharyngeal arches. By late tailbud stage, Fmr1 expression became stronger in the CNS and craniofacial regions including the ear vesicle and eye. In addition, the notochord expressed high levels of Fmr1 transcripts in the late tailbud stage embryos. In the tadpole brain, the olfactory bulb and cerebellum exhibited strong Fmr1 expression. The developmental expression pattern of Fmr1 is consistent with the wide range of abnormalities observed in FXS. Further, our findings indicate that Xenopus will serve as an excellent model to study the developmental basis of this disease.
PubMed ID: 16281176
Article link: Int J Dev Biol.
Grant support: MH065094-02 NIMH NIH HHS, NS39321 NINDS NIH HHS , P01 NS039321-050002 NINDS NIH HHS , P20 RR015578-060002 NCRR NIH HHS , RR15578 NCRR NIH HHS , P01 NS039321 NINDS NIH HHS , P20 RR015578 NCRR NIH HHS
Genes referenced: fmr1 tfap2a
Article Images: [+] show captions
|Fig. 1 (Above). ClustalW alignment of translated Fmr1 gene from human, mouse, Xenopus, zebrafish and Drosophila. (A) The common motifs of FMRP conserved in all analyzed species are highlighted by colored boxes (orange: NLS, nuclear localization signal; red: KH1, K Homology domain 1; blue: KH2, K homology domain 2; green: NES, nuclear export signal; purple: RGG box). (B) Phylogenetic tree of FMRP sequences from above species constructed by DS Gene 1.5 program. The total number of differences between sequences is indicated by the scale bar and the bootstrap support values are shown at the node of the tree as a percentage. The amino acid sequences of human, mouse, Xenopus, zebrafish FMRP and Drosophila dFMR1 were obtained from GenBank database with accession numbers AAB18832, AAL66364, P51113, NP_694495 and AAF14639, respectively.|
|Fig. 2 (Left). Northern blot analysis of Fmr1 expression during Xenopus embryonic development. Fmr1 transcripts are approximately 2.1kb (bottom band; top band is non-specific) and are present maternally (1 cell). Zygotic expression begins at early gastrula (st. 10) and gradually increases through tadpole stage (st. 47). A noticeable spike in Fmr1 trancript levels is observed from st. 20 to st. 27.|
|Fig. 3. Whole mount in situ hybridization of developing Xenopus embryos for Fmr1. (A) Early tailbud stage embryo (st. 26) showing Fmr1 expression in the CNS (white arrowheads) and pharyngeal arches (black arrowheads). (B) Expression of AP-2α, a neural crest marker at tailbud stage (st. 26). In comparison to Fmr1 expression pattern, AP-2α expression is mostly limited to the pharyngeal arches at this stage (black arrowheads). (C) Fmr1 expression at early tadpole stage embryo (st. 26; see F and G for details). (D) Horizontal section of st. 26 embryo at the level of cement gland showing Fmr1 expression in endodermal (black arrowhead), mesodermal (black arrow) and mesenchymal (white arrowhead) regions of the pharyngeal arches, with slight staining in the ectodermal region. The difference in staining intensity between the left and right side is due to the oblique nature of the sectioned tissue. Cement gland (cg) is negative for Fmr1 expression. (E) Oblique transverse section of tailbud stage embryo (st. 26). Strong expression is observed in the eye evagination (ey) and in CNS (white arrowhead). Insets show approximate region that has been sectioned (mg: midgut). (F,G) Sagittal section of late tailbud stage embryo depicted in Fig. 3C showing strong expression in the CNS (G: white arrowhead), craniofacial regions, notochord (F,G: black arrowheads), ear vesicle (F: ev) and eye (G: ey).|
|Fig. 4. Whole-mount in situ hybridization of Fmr1 in tadpole brain. The forebrain, midbrain and hindbrain (lateral view) show moderate to heavy Fmr1 expression. Abbreviations: ob, olfactory bulb; cb, cerebellum. A B C D E F G|