Identification and expression of six family genes in mouse retina

Abstract

We identified five cDNA clones of the Six gene family which are expressed in retina. They are Six2, Six3ct and Six3[~ (which are derived from alternative splicing forms), Six5, and AREC3/Six4. All of these Six family genes possess extensive sequence similarity among each other in the so-homologous region (Six domain and homeodomain) but differ greatly in structure in some other regions. The amino acid sequence similarity of the so-homologous region to the previously identified AREC31Six4 is 70.1% for Six2, 57.3% for Six3ct and Six3[~, and 70.3% for Six5. The expression of these genes was observed in inner and outer nuclear layer, ganglion cell layer, and pigment epithelium of mouse retina by in situ hybridization. The so-homologous region of each Six family protein has specific DNA binding activity. Six5 and Six2 bind to the same sequence as does AREC31Six4, while Six3 does not. These observations suggest that some of the Six family genes can regulate the same target genes.cloned. The roles of these Six family genes in retina formation are discussed. Materials and methods Screening of the cDNA library and DNA sequencingThe mouse retina eDNA library from 1-month-old BALB/c mice was kindly supplied by Dr. Ananda Swaroop [7]. A SalI-DraI (-17 2486) fragment of AREC3 eDNA (pSVSPORTMI8) [3] was labeled with [32P]dCTP with a Megaprime labeling kit (Amersham). About 1.2x 10 6 plaques were screened and we obtained 13 positive clones. They were grouped into 4 based on restriction mapping and partial nucleotide sequencing. The overlapping clones were sequenced and we obtained four species of Six family cDNAs. The nucleotide sequence data reported in this paper will appear in the DDBJ, EMBL and GenBank nucleotide sequence databases with the following accession numbers: D83147 (Six2), D83144 (Six3cq, D83145 (Six313) and D83146 (Six5).

The Transcription Factorsix1Inhibits Neuronal and Promotes Hair Cell Fate in the Developing Zebrafish (Danio rerio) Inner Ear

“…By using a smaller probe that only included the 3Ј UTR, we observed an even more restricted pattern, mainly to just the inner ear (data not shown). This leads us to think that six1 could have several splice variants, as described for Six3 in the mouse retina (Kawakami et al, 1996) or a closely related paralog as reported for six4 (Kobayashi et al, 2000). …”

Conservation and non-conservation of genetic pathways in eye specification

“…Surprisingly, one of the so orthologues, Six1, is not expressed during vertebrate eye morphogenesis, and homozygous deletion of Six1 has no affect on eye development (Oliver et al, 1995;Laclef et al, 2003). Six2 is expressed in the inner and outer nuclear layers (INL and ONL) and the ganglion cell layer (GCL) of the adult mouse retina (Kawakami et al, 1996), but ectopic expression of Six2 in developing medaka fish has no affect on eye morphogenesis (Loosli et al, 1999). Thus, it is unlikely that Six1 or Six2 is an essential part of a signaling network in vertebrate eye morphogenesis.…”

Six1is required for the early organogenesis of mammalian kidney

“…In Drosophila, so functions synergistically with the fly Pax6 gene eyeless (ey), eyes absent (eya) and dachshund (dac) to regulate the eye morphogenesis (reviewed by Treisman, 1999). The mammalian Six gene family consists of six members (Six1-6) which share two highly conserved domains, a homeodomain (HD) and a specific Six-domain (SD) crucial for proteinprotein interaction (Kawakami et al, 1996;Chen et al, 1997;Pignoni et al, 1997). Besides the eye, the Six genes are widely coexpressed with Pax, Eya and Dach (the mammalian Dachshund) genes in many tissues during mammalian organogenesis, suggesting possible interaction between their gene products and the existence of a conserved Pax-Eya-Six regulatory hierarchy (Oliver et al, 1995a;Oliver et al, 1995b;Xu et al, 1997a;Xu et al, 1997b;Xu et al, 1999;Xu et al, 2002).…”