title: Conserved expression of mouse Six1 in the pre-placodal region (PPR) and identification of an enhancer for the rostral PPR.
abstract: All cranial sensory organs and sensory neurons of vertebrates develop from cranial placodes. In chick, amphibians and zebrafish, all placodes originate from a common precursor domain, the pre-placodal region (PPR), marked by the expression of Six1/4 and Eya1/2. However, the PPR has never been described in mammals and the mechanism involved in the formation of PPR is poorly defined. Here, we report the expression of Six1 in the horseshoe-shaped mouse ectoderm surrounding the anterior neural plate in a pattern broadly similar to that of non-mammalian vertebrates. To elucidate the identity of Six1-positive mouse ectoderm, we searched for enhancers responsible for Six1 expression by in vivo enhancer assays. One conserved non-coding sequence, Six1-14, showed specific enhancer activity in the rostral PPR of chick and Xenopus and in the mouse ectoderm. These results strongly suggest the presence of PPR in mouse and that it is conserved in vertebrates. Moreover, we show the importance of the homeodomain protein-binding sites of Six1-14, the Six1 rostral PPR enhancer, for enhancer activity, and that Dlx5, Msx1 and Pax7 are candidate binding factors that regulate the level and area of Six1 expression, and thereby the location of the PPR. Our findings provide critical information and tools to elucidate the molecular mechanism of early sensory development and have implications for the development of sensory precursor/stem cells.
authors.affiliation: Division of Biology, Center for Molecular Medicine, Jichi Medical University, 3311-1 Yakushiji, Shimotsuke, Tochigi 329-0498, Japan. ssato@jichi.ac.jp
authors.forename: Shigeru
authors.initials: S
authors.lastname: Sato
authors.forename: Keiko
authors.initials: K
authors.lastname: Ikeda
authors.forename: Go
authors.initials: G
authors.lastname: Shioi
authors.forename: Haruki
authors.initials: H
authors.lastname: Ochi
authors.forename: Hajime
authors.initials: H
authors.lastname: Ogino
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Yajima
authors.forename: Kiyoshi
authors.initials: K
authors.lastname: Kawakami
mesh_terms: D000818:Animals; D002642:Chick Embryo; D004475:Ectoderm / Q000378:metabolism; D004742:Enhancer Elements, Genetic; D005786:Gene Expression Regulation; D023281:Genomics; D018398:Homeodomain Proteins / Q000378:metabolism*; D051379:Mice; D008822:Mice, Transgenic; D008954:Models, Biological; D017434:Protein Structure, Tertiary; D034741:RNA, Small Interfering / Q000378:metabolism; D011984:Sensory Receptor Cells / Q000378:metabolism; D013234:Stem Cells / Q000166:cytology; D014981:Xenopus
chemical_list: D018398:Homeodomain Proteins; D034741:RNA, Small Interfering; C490947:Six1 protein, mouse