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.