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.

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Mouse Embryonic Stem Cells (ESCs) are pluripotent mammalian cells derived from the Inner Cell Mass (ICM) of mouse blastocysts, which give rise to all three embryonic germ layers both in vivo and in vitro. Mouse ESCs have a distinct epigenetic landscape and a more decondensed chromatin compared to differentiated cells. Numerous studies have shown that distinct histone modifications in ESCs serve as hallmarks of pluripotency. However, so far it is still unknown whether the total histone content (as opposed to histone modifications) remains the same in cells of different developmental stage and differentiation capacity. In this work we show that total histone content differs between pluripotent and differentiated cells. In vitro spontaneous differentiation from ESCs to Embryoid Bodies (EBs) and directed differentiation toward neuronal and endodermal cells entails an increase in histone content. Primary MEFs also contain more histones than ESCs. We suggest that the difference in histone content is an additional hallmark of pluripotency, in addition to and besides histone modifications.