Alessandro Bulfone

The vertebrate telencephalon is composed of many architectonically and functionally distinct areas and structures, with billions of neurons that are precisely connected. This complexity is fine-tuned during development by numerous genes. To identify genes involved in the regulation of telencephalic development, a specific subset of differentially expressed genes was characterized. Here, we describe a set of cDNAs encoded by genes preferentially expressed during development of the mouse telencephalon that was identified through a functional genomics approach. Of 832 distinct transcripts found, 223 (27%) are known genes. Of the remaining, 228 (27%) correspond to expressed sequence tags of unknown function, 58 (7%) are homologs or orthologs of known genes, and 323 (39%) correspond to novel rare transcripts, including 48 (14%) new putative noncoding RNAs. As an example of this latter group of novel precursor transcripts of micro-RNAs, telencephalic embryonic subtractive sequence (TESS) 24.E3 was functionally characterized, and one of its targets was identified: the zinc finger transcription factorZFP9. The TESS transcriptome has been annotated, mapped for chromosome loci, and arrayed for its gene expression profiles during neural development and differentiation (in Neuro2a and neural stem cells). Within this collection, 188 genes were also characterized on embryonic and postnatal tissue byin situhybridization, demonstrating that most are specifically expressed in the embryonic CNS. The full information has been organized into a searchable database linked to other genomic resources, allowing easy access to those who are interested in the dissection of the molecular basis of telencephalic development.

By using a custom‐made array containing cDNAs preferentially expressed in the mouse embryonic telencephalon (Porteus et al. [1992] Brain Res Mol Brain Res 12:7–22; and Alessandro Bulfone, unpublished data), we studied the gene expression profile of the Dlx1/Dlx2^−/− subpallium and Pax6^−/− pallium. We identified a transcript corresponding to Unigene Cluster Mm.94021 and rat Evf‐1, which is down‐regulated in the Dlx1/Dlx2^−/− subpallium and up‐regulated in the Pax6^−/− pallium. Here, we report the expression pattern of this transcript, designated mouse Evf1 (mEvf1), in the prenatal forebrain of wild‐type, Dlx1/Dlx2^−/− and Pax6^−/− mice using RNA in situ hybridization and reverse transcriptase‐polymerase chain reaction. In the wild‐type forebrain mEvf1 expression is restricted to the ventral thalamus, hypothalamus, and subpallial telencephalon (caudal, lateral, and medial ganglionic eminences and septal primordia), whereas it is down‐regulated in the Dlx1/Dlx2^−/− subpallium (mainly in caudal, lateral, and medial ganglionic eminences), and up‐regulated in the Pax6^−/− lateral and ventral pallium at embryonic day 12.5 and in the dorsal, lateral, and ventral pallium at embryonic day 14.5. Developmental Dynamics 231:614–620, 2004.

Vax2 is a homeobox gene whose expression is confined to the ventral region of the prospective neural retina. Overexpression of this gene at early stages of development in Xenopus and in chicken embryos determines a ventralisation of the retina, thus suggesting its role in the molecular pathway that underlies eye development. We describe the generation and characterisation of a mouse with a targeted null mutation of the Vax2 gene. Vax2 homozygous mutant mice display incomplete closure of the optic fissure that leads to eye coloboma. This phenotype is not fully penetrant, suggesting that additional factors contribute to its generation. Vax2 inactivation determines dorsalisation of the expression of mid-late (Ephb2 and Efnb2) but not early (Pax2 and Tbx5) markers of dorsal-ventral polarity in the developing retina. Finally, Vax2 mutant mice exhibit abnormal projections of ventral retinal ganglion cells. In particular, we observed the almost complete absence of ipsilaterally projecting retinal ganglion cells axons in the optic chiasm and alteration of the retinocollicular projections. All these findings indicate that Vax2 is required for the proper closure of the optic fissure, for the establishment of a physiological asymmetry on the dorsal-ventral axis of the eye and for the formation of appropriate retinocollicular connections.