XB-ART-14956Curr Biol April 9, 1998; 8 (8): 459-62.
Cooperation of intrinsic and extrinsic signals in the elaboration of regional identity in the posterior cerebral cortex.
Understanding the compartmentalization of the neocortex (isocortex) of the mammalian brain into functional areas is a challenging problem [1-3] . Unlike pattern formation in the spinal cord and hindbrain, it does not involve the specification of distinct cells types: distinct areas differ in their patterns of connectivity and cytoarchitecture. It has been suggested that signals intrinsic to the neocortical neuroepithelium specify regional fate . Alternatively, spatial patterning might be imposed by extrinsic cues such as thalamocortical projections [4-6]. Recent results highlight the ability of early precursor cells of the telencephalic neuroepithelium to ''remember'' their spatial position from times before thalamic innervation [7,8] [9-12]. An influence from the thalamus, however, cannot be ruled out as there is a precise invasion of the correct cortical areas by the corresponding projections [13,14]. Furthermore, cortical neuronal progenitors have been proposed to adopt new connection patterns after transplantation [6,7], as well as when the thalamic input is rerouted [15,16]. Here, we describe the transient expression of the homeobox gene Otx2 in the posterior, prospective visual, neocortex and use it to analyze the establishment of posterior cortical fate. The results suggest that whereas intrinsic cortical information is sufficient to specify regional fate, extrinsic signals from the thalamus are involved in the expansion or maintenance of the population of cells expressing Otx2 but not in regionalization.
PubMed ID: 9550705
Article link: Curr Biol
Genes referenced: epha8 otx2
Antibodies: Otx2 Ab4
Article Images: [+] show captions
|Expression of Otx2 protein in the developing brain and visual centers. (a) Expression of Otx2 (epitope MMSYLKQPPYAVNGLSLTASGMDLLHQSV, in single letter amino-acid code) in a stage ~34 frog (Xenopus laevis) tadpole seen in side view after peroxidase immunocytochemistry. Labeling is in the forebrain (fb) and midbrain (mb) but not in the hindbrain (hb). (b) Expression of Otx2 in superficial cells in the tectum (tct; or superior colliculus) of an embryonic day 17 (E17) Sprague–Dawley rat embryo in a sagittal section after fluorescence immunocytochemistry. (c) The same field as in (b) showing the position of DAPI-labeled nuclei. (d) Expression of Otx2 in choroid plexus (chp) and adjacent granule cells (gc) of the cerebellum as seen in a sagittal section of an E17 rat embryo. (e) Expression of Otx2 in the developing eye of a 24 h zebrafish embryo seen in crosssection. Expression is detected in the photoreceptor layer (ph) and inner layer (inl). (f) Expression of Otx2 in the posterior cerebellum of a postnatal day 6 (P6) rat as seen in a sagittal section. The image shows double labeling of Otx2 in green and cell nuclei in blue (DAPI stain). Expression is high in the internal granular layer (igl) and very weak or absent in the external germinal layer (egl). (g) Expression of Otx2 in the developing lateral geniculate nucleus (LGN) of a P6 rat seen in crosssection. Note the higher expression in the ventral region. The insets in (d,g) show Otx2 in nuclei.|