The mouse Laf4 gene:: Exon/intron organization, cDNA sequence, alternative splicing, and expression during central nervous system development

The cerebral cortex is a tissue with a high degree of neuronal diversity. It consists of six cell layers with a unique set of neuronal subtypes. A crucial step in the process of cortical differentiation is the transition from a mitotically active neuroblast to a postmitotic young neuron. To identify genes involved in the control of this transition, we applied a novel method of cDNA subtraction based on mirror-orientation selection. One of the genes we have identified in our screening proved to be a mouse homolog of the human putative transcription factor LAF4. We identified alternatively spliced forms of mouse Laf4 that encode several forms of putative protein with potentially different transactivation functions. Two forms are expressed mainly during embryogenesis, whereas the other forms are expressed mainly in adults. We have found that Laf4 transcription becomes very quickly upregulated as soon as young cortical neurons leave the ventricular zone (VZ), the cortical-proliferative compartment. This coincides with the initial steps of cortical differentiation. Laf4 becomes downregulated in postnatal cortex, indicating its involvement in the transcriptional regulation of the early steps of cortical differentiation. We have also examined Laf4 expression in the brains of Sey and reeler mutants. Laf4 was downregulated in the lateroventral part of the cerebral cortex and completely lost in the piriform cortex of the Sey mutant embryos. We also compared its expression during central nervous system development with that of its closest homolog, Fmr2, a gene implicated in mental retardation in humans.