Searching for the prototypic eye genetic network: Sine oculis is essential for eye regeneration in planarians.
We have identified a sine oculis gene in the planarian Girardia tigrina (Platyhelminthes; Turbellaria; Tricladida). The planarian sine oculis gene (Gtso) encodes a protein with a sine oculis (Six) domain and a homeodomain that shares significant sequence similarity with so proteins assigned to the Six-2 gene family. Gtso is expressed as a single transcript in both regenerating and fully developed eyes. Whole-mount in situ hybridization studies show exclusive expression in photoreceptor cells. Loss of function of Gtso by RNA interference during planarian regeneration inhibits eye regeneration completely. Gtso is also essential for maintenance of the differentiated state of photoreceptor cells. These results, combined with the previously demonstrated expression of Pax-6 in planarian eyes, suggest that the same basic gene regulatory circuit required for eye development in Drosophila and mouse is used in the prototypic eye spots of platyhelminthes and, therefore, is truly conserved during evolution.
Pineda
D
D
Departament de Genètica, Facultat de Biologia, Universitat de Barcelona, Diagonal 645, 08071 Barcelona, Spain.
Gonzalez
J
J
Callaerts
P
P
Ikeo
K
K
Gehring
W J
WJ
Salo
E
E
D000595:Amino Acid Sequence; D000818:Animals; D005075:Biological Evolution; D017124:Conserved Sequence; D004330:Drosophila; D029721:Drosophila Proteins; D019143:Evolution, Molecular; D005123:Eye / Q000196:embryology*; D005136:Eye Proteins / Q000235:genetics*; D005801:Genes, Homeobox; D018398:Homeodomain Proteins / Q000235:genetics*; D006801:Humans; D051379:Mice; D008969:Molecular Sequence Data; D005810:Multigene Family; D010802:Phylogeny; D010932:Planarians / Q000235:genetics / Q000502:physiology*; D012038:Regeneration; D016415:Sequence Alignment; D017386:Sequence Homology, Amino Acid
D029721:Drosophila Proteins; D005136:Eye Proteins; D018398:Homeodomain Proteins; C087345:So protein, Drosophila