Research Report Spatial and temporal patterns of proliferation and differentiation in the developing turtle eye Javier Francisco-Morcillo a , Matías Hidalgo-Sánchez b , Gervasio Martín-Partido b, ⁎ a Departamento de Biología Celular, Facultad de Veterinaria, Universidad de Extremadura, Avda. de la Universidad s/n, 10071 Cáceres, Spain b Departamento de Biología Celular, Facultad de Ciencias, Universidad de Extremadura, Avda. de Elvas s/n, 06071 Badajoz, Spain ARTICLE INFO ABSTRACT Article history: Accepted 11 May 2006 Available online 22 June 2006 Here we show for the first time different aspects of the pattern of neurogenesis in the developing turtle retina by using different morphological and molecular clues. We show the chronotopographical fashion of occurrence of three major aspects of retinal development: (1) morphogenesis of the optic primordia and emergence of the different retinal layers, (2) the temporal progression of neurogenesis by the cessation of proliferative activity, and (3) the apparition and cellular localization of different antigens and neuroactive substances. Retinal cells were generated in a conserved temporal order with ganglion cells born first, followed by amacrine, photoreceptor, horizontal and bipolar/Müller cells. While eventually expressed in many types of retinal neurons, Islet1 was permanently expressed in differentiating and mature ganglion cells. Calbindin-immunoreactive elements were found in the ganglion cell layer and the inner nuclear layer. Interestingly, at later stages the amount of expressing cells in these layers was reduced dramatically. On the contrary, the number of calbindin-immunoreactive photoreceptors increased as development proceeded. In addition, calretinin expressing cells were prominent in the horizontal cell bodies, and their processes extending into the outer plexiform layer were also strongly labeled. Finally, the synthesis of γ-aminobutyric acid (GABA) was detected in developing and matured horizontal and amacrine cells. All these maturational features began in the dorso- central area, in a region slightly displaced towards the temporal retina. © 2006 Elsevier B.V. All rights reserved. Keywords: Retina Calbindin Calretinin Islet1 GABA Mauremys leprosa BRAIN RESEARCH 1103 (2006) 32 – 48 ⁎ Corresponding author. Fax: +34 924 289411. E-mail address: gmartin@unex.es (G. Martín-Partido). 0006-8993/$ – see front matter © 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.brainres.2006.05.052 available at www.sciencedirect.com www.elsevier.com/locate/brainres