J. Anat. (2002) 200, pp51– 56 © Anatomical Society of Great Britain and Ireland 2002 Blackwell Science Ltd The transcription factor cSox2 and Neuropeptide Y define a novel subgroup of amacrine cells in the retina D. Le Rouëdec, 2 K. Rayner, 1 M. Rex, 3 P. M. Wigmore 2 and P. J. Scotting 1 1 The Nottingham Children’s Brain Tumour Research Centre, Institute of Genetics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK 2 School of Biomedical Sciences, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK 3 Biological Sciences, University of Warwick, Coventry, UK Abstract The retina has been extensively used as a model to study the mechanisms responsible for the production of differ- ent neural cell phenotypes. The importance of both extrinsic and intrinsic cues in these processes is now appreci- ated and numerous transcription factors have been identified which are required for both neuronal determination and cell differentiation. In this study we have analysed the expression of the transcription factor Sox2 during devel- opment of the chick retina. Expression was found in the proliferating cells of the retina during development and was down regulated by nearly all cell types as they started to differentiate and migrate to the different layers of the retina. In one cell type, however, Sox2 expression was retained after the cells have ceased division and migrated to their adult location. These cells formed two rows located on either side of the inner plexiform layer and were also positive for Neuropeptide Y, characteristics which indicate that they were a subpopulation of amacrine cells. The expression of Sox2 by only this population of post-mitotic neurones makes it possible to follow these cells as they migrate to their adult location and shows that they initially form a single row of cells which subsequently divides to form the double row seen in the adult tissue. We suggest that retained expression of Sox2 is involved in directing the differentiation of these cells and is an early marker of this cell type. Key words amacrine cells; chick; Neuropeptide Y; retina; Sox2. Introduction The retina is a relatively simple laminated tissue composed of only six types of neurones and one type of glia, features which have made it an attractive model to study neuronal cell specification. As in other parts of the developing central nervous system, cell prolifera- tion is restricted to a germinal layer from which differ- entiating post-mitotic cells originate (Prada et al. 1991). The resulting cell types generated segregate into three layers separated by two synaptic layers. These three nuclear layers are known as: the outer nuclear layer, which contains two classes of photoreceptors, rods and cones; the inner nuclear layer, which consists of horizontal, bipolar, amacrine neurons and displaced ganglion cells; and the ganglion cell layer, which contains predominantly ganglion cells and displaced amacrine cells. All cell types within the retina originate from one population of progenitor cells and lineage analysis has demonstrated that individual progenitor cells are multipotent and can generate different com- binations of neurones and glia (Turner & Cepko, 1987). Very little is known, however, about what determines the formation of different cell types. Transcription factors have been shown to play a key role in providing intrinsic information influencing cell fate decision (reviewed in Perron & Harris, 2000; Livesey & Cepko, 2001). In particular, individual transcription factors belonging to the bHLH gene family have been shown to be expressed in proliferating cell progenitors as well as being maintained by discrete cell types after they have ceased to divide. This suggests that these transcription factors may have a role in directing progenitors towards a particular cell fate. Examples of this type of expression pattern include amacrine cells, a major class of interneurons in the retina, which retain Correspondence P. J. Scotting, The Nottingham Children’s Brain Tumour Research Centre, Institute of Genetics, University of Nottingham, Queen’s Medical Centre, Nottingham NG7 2UH, UK. Accepted for publication 8 August 2001