Research report A collection of cDNAs enriched in upper cortical layers of the embryonic mouse brain Cristina Garcı ´a-Frigola a,b , Ferran Burgaya a , Marta Calbet a , Guillermo Lo ´pez-Dome `nech a , Luis de Lecea b , Eduardo Soriano a, * a IRBB/PCB and Department of Cell Biology, Faculty of Biology, University of Barcelona, 08071 Barcelona, Spain b Department of Molecular Biology, The Scripps Research Institute, 10550 North Torrey Pines Road, La Jolla, CA 92037, USA Accepted 12 December 2003 Abstract In an attempt to elucidate the molecular basis of neuronal migration and corticogenesis, we performed subtractive hybridization of mRNAs from the upper cortical layers (layer I and upper cortical plate) against mRNAs from the remaining cerebral cortex at E15– E16. We obtained a collection of subtracted cDNA clones and analyzed their 3VUTR sequences, 47% of which correspond to EST sequences, and may represent novel products. Among the cloned sequences, we identified gene products that have not been reported in brain or in the cerebral cortex before. We examined the expression pattern of 39 subtracted clones, which was enriched in the upper layers of the cerebral cortex at embryonic stages. The expression of most clones is developmentally regulated, and especially high in embryonic and early postnatal stages. Four of the unknown clones were studied in more detail and identified as a new member of the tetraspanin superfamily, a putative RNA binding protein, a specific product of the adult dentate gyrus and a protein containing a h-catenin repeat. We thus cloned a collection of subtracted cDNAs coding for protein products that may be involved in the development of the cerebral cortex. D 2004 Elsevier B.V. All rights reserved. Theme: Development and regeneration Topic: Cell differentiation and migration Keywords: cDNA subtraction in cerebral cortex 1. Introduction During the formation of the cerebral cortex, postmitotic neurons originate in the ventricular zone, migrate toward the marginal zone (layer I) and settle in the cortical plate following an inside-out order, in which younger neurons bypass previously positioned neurons [5,53,64]. To orches- trate such an organized migratory process, multiple cellular events are required, including cell-to-cell recognition, adhe- sion and detachment, guidance by extracellular factors, signaling cascades and cell motility [3,7 – 10,13,28]. The final location of each cortical neuron in the mature brain, conditioned by these processes, greatly determines its mor- phology and patterns of synaptic connections [15,65,72]. The first molecular cues that govern these processes have been identified through the study of spontaneous and genet- ically engineered mutations in human and mouse models that show abnormal cortical development. Research has focused on mutants with neuronal malpositioning and migratory defects, which have unraveled the complexity and diversity of the gene products involved in the migratory processes: extracellular matrix proteins and receptors (Reelin, Integrin subunits, Cadherin-related neural receptors, VLDL and ApoE receptors, Astrotactin) proteins related to the cyto- skeleton (Filamin-1 and Doublecortin), adaptor proteins (mDab) and cell cycle regulators (Cdk5, p35) [66]. For many years, it has been suggested that cortical layer I, with its strategic superficial location, is involved in the control of cortical migration [25–27,54–57]. Recent mo- lecular evidence has shown that Reelin, an ECM molecule selectively expressed in the marginal zone, and several of its receptors and signaling molecules play a critical role in the process [1,14,15,18 – 20,28,36,37,40,41,43,44,52,60,67, 0169-328X/$ - see front matter D 2004 Elsevier B.V. All rights reserved. doi:10.1016/j.molbrainres.2003.12.014 * Corresponding author. IRBB/PCB and Department of Cell Biology, UB, c/o Josep Samitier, 1-5, 08028 Barcelona, Spain. Tel.: +34-93-403-71- 17; fax: +34-93-403-71-14. E-mail address: esoriano@pcb.ub.es (E. Soriano). www.elsevier.com/locate/molbrainres Molecular Brain Research 122 (2004) 133 – 150