EMX2 protein in the developing mouse brain and olfactory area

Abstract

The distribution of EMX2, the protein product of the homeobox gene Emx2, was analyzed in the developing mouse CNS by means of a polyclonal antibody we raised against it. The protein is present in the rostral brain, the olfactory area and a set of scattered cells lying between the nasal pits and the telencephalon. In the cortical neuroepithelium EMX2 is expressed all along the rostro-caudal axis in a graded distribution with a caudal-medial maximum and a rostral-lateral minimum. Anti-EMX2 immunoreactivity is also detectable in Cajal-Retzius cells as well as in apical dendrites of marginal neurons of the cortical plate. We also observe that the EMX2 and EMX1 homeoproteins display complementary expression patterns in olfactory bulbs and amygdaloid complex. Here, they demarcate different neuronal populations, involved in processing olfactory information coming from the vomero-nasal organ and from the main olfactory epithelium, respectively. EMX2 is also detectable in mesencephalic structures, such as the optic tectum and tegmentum. The graded distribution of EMX2 along antero-posterior and medial-lateral axes of the primitive cortex prefigures a role of this protein in the subdivision of the cortex in cytoarchitectonic regions and possibly functional areas, whereas its presence in Cajal-Retzius cells suggests a role in the process of cortical lamination.

Emx2 homeodomain transcription factor interacts with eukaryotic translation initiation factor 4E (eIF4E) in the axons of olfactory sensory neurons

“…noteworthy that these homeoproteins and several others (i.e., Otx1 and Emx1) show a nonnuclear and in some instances dendritic localization in selected classes of neurons (10,57,58, and our unpublished observations). It is possible, as proposed for Otx homeoproteins (57,58), that this cytoplasmic retention prevents homeoprotein transcriptional activity until a specific trigger allows their nuclear import.…”

“…The expression of Emx2 in the embryonic olfactory epithelium (9,10) and the impairment of olfactory system development in the Emx2-invalidated mouse (11,12) has incited us to study the expression of Emx2 mRNA and protein in the adult olfactory system. We report that Emx2 is expressed in the adult olfactory epithelium and that the protein is not only present in the OSN nuclei at the level of the epithelium but also transported into their axon and axon terminals.…”

Gradients in the Brain: The Control of the Development of Form and Function in the Cerebral Cortex

“…Notable among those genes are transcription factors expressed in opposing rostral-caudal gradients. For example, Pax6 is expressed in a rostrolateral high to caudomedial low gradient; Emx2 has a caudomedial high to rostrolateral low gradient; and COUP-TFI displays a caudolateral high to rostromedial low gradient (Walther and Gruss 1991;Simeone et al 1992;Stoykova and Gruss 1994;Gulisano et al 1996;Mallamaci et al 1998;Liu et al 2000). Other classes of genes commonly associated with development, such as the Ephs and Ephrins, and Cadherins, were also found to be expressed in gradients in neocortical stem cells (Mackarehtschian et al 1999;Nakagawa et al 1999).…”

Evolutionary conservation of mechanisms for neural regionalization, proliferation and interconnection in brain development

“…In the absence of ems, the number of projection neurons is severely reduced and the remaining projection neurons innervate inappropriate olfactory glomeruli (figure 2b). In the mouse, the Emx1/2 genes are expressed in developing mitral cells, and the loss of these genes leads to marked defects in the mitral cell layer (Mallamaci et al 1998;Bishop et al 2003). Similar roles of the ems/Emx genes in the development of second-order olfactory neurons, together with a comparable requirement of ems/Emx genes in olfactory sense organ development, argue for evolutionarily 114 H. Reichert Opinion piece.…”