Proto-mapping the areas of cerebral cortex: transcription factors make the grade

Transcription factor Lmo4 defines the shape of functional areas in developing cortices and regulates sensorimotor control

Proper formation of the shape and size of cortical functional areas is essential for complex brain function, including sensory perception and motor control. Our previous work identified the transcription factor Lim domain only 4 (Lmo4), a regulator in calcium-dependent gene transcription, that has unique, region-specific expression in postnatal mouse cortices with high expression anteriorly and posteriorly but very low expression in between. Here we report that Lmo4 expression coincides with the timing of the development of the somatosensory barrel field. Lmo4 cortical deletion causes changes in expression patterns of cortical regional markers and results in rostro-medial shrinkage but not rostral or caudal shift of the somatosensory barrel subfield. Fine regulation of accurate shape of the barrel subfield by Lmo4, as well as Lmo4-mediated calcium-dependent gene expression, is critical for normal brain functions, as Lmo4-deficient mice display impaired sensorimotor performance. Moreover, even though Lmo4 has broad expression in the central nervous system, it plays a subtle role in the development of non-cortical regions. Our results reveal a new mechanism of cortical area formation and normal sensorimotor control that is regulated by genes with region-specific expression in the developing cortex.

Unraveling the molecular pathways that regulate early telencephalon development

The telencephalon, at the rostral end of the developing central nervous system, starts off as a sheet of neuroepithelial cells. During development, this sheet of cells becomes patterned and morphologically partitioned into areas that give rise to the adult cerebral hemispheres. How does this happen? How are telencephalic precursor cells instructed to generate myriad neural cell types in different areas and at different times as well as to change their rates of cell proliferation, differentiation, and death? The molecular pathways required for patterning the telencephalic neuroepithelium and forming the cerebral hemispheres are beginning to be unraveled.

FGF signaling through FGFR1 is required for olfactory bulb morphogenesis

During development, the embryonic telencephalon is patterned into different areas that give rise to distinct adult brain structures. Several secreted signaling molecules are expressed at putative signaling centers in the early telencephalon. In particular, Fgf8 is expressed at the anterior end of the telencephalon and is hypothesized to pattern it along the anteroposterior (AP) axis. Using a CRE/loxP genetic approach to disrupt genes in the telencephalon, we address the role of FGF signaling directly in vivo by abolishing expression of the FGF receptor Fgfr1. In the Fgfr1-deficient telencephalon, AP patterning is largely normal. However, morphological defects are observed at the anterior end of the telencephalon. Most notably, the olfactory bulbs do not form normally. Examination of the proliferation state of anterior telencephalic cells supports a model for olfactory bulb formation in which an FGF-dependent decrease in proliferation is required for initial bulb evagination. Together the results demonstrate an essential role for Fgfr1 in patterning and morphogenesis of the telencephalon.