We generated mice carrying a loss-of-function mutation in Brn-2, a gene encoding a nervous system specific POU transcription factor, by gene targeting in embryonic stem cells. In homozygous mutant embryos, migratory precursor cells for neurons of the paraventricular nuclei (PVN) and the supraoptic nuclei (SO) of the hypothalamus die at -E12.5. All homozygous mutants suffered mortality within 10 days after birth, possibly because of a complete deficiency of these neurons in the hypothalamus. Although neither developmental nor histological abnormalities were observed in heterozygous mice, the levels of expression of vasopressin and oxytocin in the hypothalamus of these animals were half these of wild-type mice. These results strongly suggest that Brn-2 plays an essential role in the determination and development of the PVN and SO neuronal lineages in the hypothalamus.

Traumatic damage to the central nervous system (CNS) destroys the blood–brain barrier (BBB) and provokes the invasion of hematogenous cells into the neural tissue. Invading leukocytes, macrophages and lymphocytes secrete various cytokines that induce an inflammatory reaction in the injured CNS and result in local neural degeneration, formation of a cystic cavity and activation of glial cells around the lesion site. As a consequence of these processes, two types of scarring tissue are formed in the lesion site. One is a glial scar that consists in reactive astrocytes, reactive microglia and glial precursor cells. The other is a fibrotic scar formed by fibroblasts, which have invaded the lesion site from adjacent meningeal and perivascular cells. At the interface, the reactive astrocytes and the fibroblasts interact to form an organized tissue, the glia limitans. The astrocytic reaction has a protective role by reconstituting the BBB, preventing neuronal degeneration and limiting the spread of damage. While much attention has been paid to the inhibitory effects of the astrocytic component of the scars on axon regeneration, this review will cover a number of recent studies in which manipulations of the fibroblastic component of the scar by reagents, such as blockers of collagen synthesis have been found to be beneficial for axon regeneration. To what extent these changes in the fibroblasts act via subsequent downstream actions on the astrocytes remains for future investigation.

Protein L-isoaspartyl methyltransferase (PIMT) is suggested to play a role in the repair of aged protein spontaneously incorporated with isoaspartyl residues. We generated PIMT-deficient mice by targeted disruption of the PIMT gene to elucidate the biological role of the gene in vivo. PIMT-deficient mice died from progressive epileptic seizures with grand mal and myoclonus between 4 and 12 weeks of age. An anticonvulsive drug, dipropylacetic acid (DPA), improved their survival but failed to cure the fatal outcome. L-Isoaspartatate, the putative substrate for PIMT, was increased ninefold in the brains of PIMT-deficient mice. The brains of PIMT-deficient mice started to enlarge after 4 weeks of age when the apical dendrites of pyramidal neurons in cerebral cortices showed aberrant arborizations with disorganized microtubules. We conclude that methylation of modified proteins with isoaspartyl residues is essential for the maintenance of a mature CNS and that a deficiency in PIMT results in fatal progressive epilepsy in mice.

No abstract

The mode of Purkinje cell migration in the mouse cerebellar primordium was examined immunohistochemically, by marking Purkinje cells with anti-spot 35 antibody and labeling them with 5'-bromodeoxyuridine. The cells migrated radially from the neuroepithelium of the fourth ventricle towards the cortical surface between the 13th and 17th days (E13-E17) of gestation. Regional differences in the migratory process were evident: the final settlement of the Purkinje cells proceeded earlier in the lateral and posterior parts of the primordium, exhibiting latero-medial and posteroventral-anterodorsal diminishing sequences. To elucidate the factors involved in the migration, the arrangement of radial glial fibers, and expression of the cell adhesion molecule, tenascin, were examined immunohistochemically with the monoclonal antibody 1D11, a marker for both immature and mature astroglia, and an anti-tenascin antibody. At E14, 1D11-immunopositive fibers were seen to extend from the ventricle to the pial surface, and the cell bodies of immature glia migrated after E15 towards the cortex, shortening the radial processes whose end-feet were attached to the pia mater. Tenascin, which possesses a neuron-glial adhesiveness, was also expressed on the radial fibers during the migration of the Purkinje cells. The fibers were closely apposed to the migratory Purkinje cells, and their arrangement and orientation accorded with the migratory direction of the Purkinje cells. Further, changes in the molecular species of antigens detected by both the 1D11 and anti-tenascin antibodies were observed by immunoblotting analysis during the course of cerebellar development. These findings suggest that the arrangement of radial glia and expression of adhesion molecules may be involved in the control and guidance of Purkinje cell migration.