Journal of Neurochemistry, 2005, 94, 1739–1745 doi:10.1111/j.1471-4159.2005.03336.x
Runx1 expression defines a subpopulation of displaced amacrine cells in the developing mouse retina
Lee Stewart,* Mary Anne Potok, Sally A. Camper and Stefano Stifani*
*Center for Neuronal Survival, Montreal Neurological Institute, Montreal, Quebec, Canada Department of Human Genetics, University of Michigan Medical School, Ann Arbor, Michigan, USA
Abstract primarily in the ganglion cell layer by late embryonic/early AML1/Runx1 (Runx1) is a mammalian transcription factor that post-natal stages and were identified as a subpopulation of plays critical roles in regulating the differentiation of a number displaced amacrine cells by the continued expression of of different cell types. In the present study, we have utilized Islet1, as well as Pax6, and the coexpression of the amacrine mice expressing b-galactosidase (b-gal) under the control of cell subtype-specific markers choline acetyltransferase, cal- the Runx1 promoter to characterize the spatiotemporal retinin and the 65-kDa isoform of glutamic acid decarboxylase. expression pattern of Runx1 during retinogenesis. Expression These findings identify Runx1 as a novel marker for a of b-gal was first detected at embryonic day 13.5 in post- restricted amacrine cell subtype and suggest a role for this mitotic cells located in the inner retina and overlapped with gene in regulating the post-mitotic development of these cells. expression of the early amacrine and ganglion cell marker Keywords: amacrine cells, choline acetyltransferase, gan- protein Islet1. During subsequent developmental stages, the glion cell layer, 65-kDa isoform of glutamic acid decarboxy- number of b-gal-positive cells increased in a central-to-per- lase, retina, Runx1. ipheral gradient until late embryogenesis but then decreased J. Neurochem. (2005) 94, 1739–1745. in the early post-natal retina. b-gal-positive cells were located
The differentiation of distinct neuronal subtypes at the Otto et al. 2003). In particular, Runx1 is required for correct time and place is a critical event during nervous definitive hematopoiesis in mice and mutations of its human system development. In that regard, the developing mam- homolog, AML1, are found in a high percentage of acute malian retina provides a relatively simple and well-defined myeloid leukemias and other hematological disorders experimental system to study the events that underlie the (Amman et al. 2001; Roumier et al. 2003). Recent studies generation of different cell types from common progenitors. have also identified a requirement for Runx1 function during Six main classes of neurons and one type of glial cell are the post-mitotic development of selected populations of generated in the retina and the precise spatial and temporal sensory and motor neurons in the murine hindbrain and pattern of retinogenesis is under the influence of both cranial ganglia, implicating Runx1 in the regulation of neuron extrinsic and intrinsic cues (Marquardt and Gruss 2002). subtype differentiation (Theriault et al. 2004). To determine Although a number of transcription factors have been if Runx1 is involved in the development of additional identified as important regulators of mammalian retinal development (Marquardt 2003), the mechanisms that regu- late the acquisition of specific retinal neuron traits still Received April 7, 2005; revision received May 20, 2005; accepted May 20, 2005. remain poorly defined. In particular, little is known about the Address correspondence and reprint requests to Dr Stefano Stifani, molecular characteristics of specific subtypes of each set of Center for Neuronal Survival, #F102, Montreal Neurological Institute, retinal neurons and how the differentiation of those individ- 3801 rue University, Montreal, Quebec, H3A 2B4, Canada. ual subtypes is regulated. E-mail: [email protected] The phylogenetically conserved runt/Runx gene family Abbreviations used: AMCA, Amino Methyl Coumarin Acetate; b-gal, b-galactosidase; ChAT, choline acetyltransferase; E, embryonic encodes a number of DNA-binding transcription factors that day; GAD65, 65-kDa isoform of glutamic acid decarboxylase; GAD67, play important roles during development in both inverte- 67-kDa isoform of glutamic acid decarboxylase; GCL, ganglion cell brates and vertebrates (Wheeler et al. 2000; Coffman 2003; layer; IPL, inner plexiform layer; P, post-natal day.