title: The role of Xenopus Rx-L in photoreceptor cell determination.
abstract: Members of the Rx (retinal homeobox) gene family play vital roles during eye development. In Xenopus, as in most other vertebrates, two Rx-type genes have been described. While Rx1 deficiency led to loss of optic vesicles and impaired the proper development of ventral forebrain structures, a recently isolated second Rx-gene, Rx-L, seems to function in late retinogenesis. Here, we report that the specific suppression of Xenopus Rx-L function impaired the formation of the photoreceptor layer and reduced the expression of photoreceptor specific genes. Overexpression of Xenopus Rx-L induced ectopic expression of photoreceptor specific genes, but did only marginally promote the proliferation of retinal progenitor cells. Targeted overexpression of Rx-L in developing retinoblasts in vivo led to an increased fraction of photoreceptor cells at the expense of amacrine and bipolar cells and revealed that Rx-L acts as a transcription activator. A phylogenic analysis of all reported Rx-type genes revealed that they could be grouped into three categories, including an "invertebrate Rx" group, a "classical vertebrate Rx" group, and a "vertebrate Qrx/Rx-L" group. Taken together, Rx-L, unlike Rx1, is required for the determination of retinal cell types, especially photoreceptors, rather than for proliferation of retinal progenitors.
authors.affiliation: Institut für Physiologische Chemie, Universität Halle-Wittenberg, D-06114 Halle/Saale, Germany.
authors.forename: Hui-Yuan
authors.initials: HY
authors.lastname: Wu
authors.forename: Muriel
authors.initials: M
authors.lastname: Perron
authors.forename: Thomas
authors.initials: T
authors.lastname: Hollemann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D018507:Gene Expression Regulation, Developmental; D018398:Homeodomain Proteins / Q000235:genetics / Q000378:metabolism*; D008969:Molecular Sequence Data; D010786:Photoreceptor Cells / Q000166:cytology / Q000502:physiology*; D012160:Retina / Q000166:cytology / Q000196:embryology; D012243:Rhodopsin / Q000235:genetics / Q000378:metabolism; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid; D029867:Xenopus Proteins / Q000235:genetics / Q000378:metabolism*; D014982:Xenopus laevis / Q000033:anatomy & histology / Q000196:embryology
chemical_list: D018398:Homeodomain Proteins; C539761:RAX2 protein, Xenopus; D029867:Xenopus Proteins; D012243:Rhodopsin