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We have identified a novel receptor-like protein tyrosine phosphatase (RPTPrho) transcript whose expression in the cerebellar cortex is restricted to the granule cell layer of lobules 1-6. Acidic fibroblast growth factor (FGF-1) mRNA follows a similar cerebellar expression pattern. Together, the two markers define a sharp boundary in lobule 6, slightly caudal to the primary fissure. Anterior and posterior compartments became discernible only during postnatal weeks two and six, for RPTPrho and FGF-1, respectively. A rostrocaudal boundary in lobule 6 of the murine cerebellar cortex has also been identified morphologically by the effects of the meander tail mutation. The position of the RPTPrho and FGF-1 boundary on the rostrocaudal axis of the cerebellar cortex was close to, but not coincident with, the caudal extent of the disorganized anterior lobe of meander tail and the rostral extent of Otx-2 expression. The restricted pattern of FGF-1 and RPTPrho implies that these molecules may have specific signaling roles in the tyrosine phosphorylation/dephosphorylation pathway in the anterior compartment of the adult cerebellar cortex.

The autosomal semidominant mutation Bst (belly spot and tail) is often associated with small and atrophic optic nerves in adult mice and shares several important attributes with heritable optic nerve atrophy in humans. In this article, the authors present adult and developmental studies on the retinal phenotype in Bst/+ mice.Retinal ganglion cells in adult Bst/+ mice were labeled retrogradely with horseradish peroxidase injected into the right optic tract. Labeled ganglion cells were mapped in whole-mounted retinas ipsilateral and contralateral to the injection site. The number of axons in optic nerves of these and other cases were quantified using an electron microscopic method. Eyes of neonatal, embryonic day 15 (E15), and embryonic day 12 (E12) Bst/+ mutants were examined histologically to understand the etiology of the retinal phenotype.Approximately 60% of adult Bst/+ mice have deficient direct pupillary light responses. This neurologic phenotype is associated with a reduction in the number of retinal ganglion cells from the wild-type average of 67,000 to less than 20,000 in Bst/+ mutants. Ganglion cells with crossed projections are more severely affected than those with uncrossed projections. Histologic analysis of eyes from E12 mice reveals a delayed closure of the optic fissure. Despite this abnormality, other ocular structures appear relatively normal. However, some E15 mutants exhibit marked disorganization of the retinal neuroepithelium, and ganglion cell axons are found between pigmented and neural retina. At birth, optic nerves of affected mice are smaller than those of wild-type mice, ectopic axons are found within the eyes, and the ganglion cell layer contains many dying cells.The expression of the retinal phenotype in Bst/+ mutants is highly variable-ranging from a complete absence of ganglion cells to numbers comparable to that in wild-type mice. The reduction in ganglion cell number in affected adult Bst/+ mice is attributable to the failure of ganglion cell axons to reach the optic nerve head early in development. Delayed fusion of the fissure is consistently associated with the Bst/+ genotype and probably contributes to the failure of ganglion cell axons to grow out of the eye.

Neurological mutant mice have yielded an early and continuously rich resource for studying the role of genes in the developing cerebellum. Experimentally produced chimeric mice, containing mixtures of genetically normal and mutant cells, provided a means of deducing the primary site of gene action and studying cell interactions in these mutant cerebella. Recently, three mutant genes, reeler, weaver, and staggerer, have been cloned and their gene products identified. These three genes have been examined earlier by the chimera technology. Here, we review the chimera studies in the light of what we now know to be the products of these mutant genes.

Midline structures, such as the notochord and floor plate, are crucial to the developing central nervous system (CNS). Previously, we demonstrated that annexin IV is an excellent marker of midline structures. In the present study, we explore the possible role of annexin IV in development of the CNS midline. Using immunocytochemistry with an antibody to annexin IV, we have elucidated the temporal and spatial expression of this molecule. Annexin IV is present in the notochord at embryonic day (E) 8.5, prior to its expression in any structures within the neural tube. Subsequently, annexin IV is expressed by floor plate cells at E9.5. Annexin IV is also expressed in the roof plate, but not until E10.5. To determine if normal morphogenesis of these midline structures is essential for annexin IV expression, we analyzed two strains of mutant mice that have defective formation of either the floor or the roof plate. In Danforth's short-tail mice, the floor plate is absent from the caudal spinal cord, and annexin IV immunopositivity disappears at the level where the floor plate is missing. In curly tail mutant mice, there can be a failure of the neural tube to close, and in these regions there is no annexin IV expression in presumptive roof plate cells. Finally, annexin IV immunolabeling is present from the caudal spinal cord, through the brainstem up to the diencephalon and lamina terminalis. Thus, annexin IV is an excellent marker for differentiated midline cells, is temporally and spatially correlated with development of the floor and roof plates, and is expressed in a rostral-caudal manner that supports the hypothesis that the floor plate extends the full length of the original neural tube.

The meander tail (mea) gene results in a stereotypic pattern of cerebellar abnormalities, most notably the virtual depletion of granule cells in the anterior lobe of the cerebellum. The causal basis of this mutation is unknown. In this paper we have taken a three-part approach to the analysis of mea gene action. First, we quantitatively determined the effect of the mea gene on granule cell and Purkinje cell number. We found, in addition to the marked depletion of anterior lobe granule cells (90%), there were also significantly fewer granule cells in the posterior lobe (20-30%) without a concomitant loss of Purkinje cells. Second, we explored the relationship between granule cell depletion caused by the mea gene and by the mitotic poison, 5-fluoro-2'-deoxyuridine (FdU). Prenatal and postnatal ICR mice were treated with FdU to ascertain the regimen that best produces a meander tail-like cerebellar phenotype. The similarity of the effects of the mea gene and injections of FdU at E17 and PO suggests the hypothesis that the mea gene acts to disrupt the cell cycle of cerebellar granule cell precursors. Thus, the third part of this study was to test this hypothesis by using injections of either BrdU (5-bromo-2'-deoxyuridine) or 3H-thymidine into homozygous and heterozygous meander tail littermates at E17 or PO. After processing the tissue for BrdU immunocytochemistry or 3H-thymidine autoradiography, counts were made of the number of labeled and unlabeled external granule layer (EGL) cells to determine the percentage that had incorporated the mitotic label (labeling index). No difference in the labeling index was found between homozygous meander tail mice and normal, heterozygous littermate controls. Therefore, the mitotic activity of the EGL neuroblasts is not disrupted by the mea gene. Furthermore, while a mitotic poison can produce a phenotype similar to the action of the mea gene, mea is phenomenologically different from FdU treatment.

The study of chimeric retinas has yielded insight on the early development of retina. The close match in chimerism ratios between right and left retinas is significant and supports the idea that both retinas originate from a common population of progenitors. We are able to estimate numbers of progenitor cells that contribute to the formation of the retina and the approximate time at which this small group is isolated from surrounding prosencephalic cell fields. These cells undergo at least five rounds of division before the first retinal neurons are generated. The mouse retina is not build from the center outward. There is simultaneous expansion and differentiation in all parts of the retina and as a result clones are not arranged in wedges. Instead the mouse retina is a patchwork of clones that do not differ greatly in size from center to periphery. The most consistent radial feature in mouse retina is a raphe left at the line of fusion of the margins of the ventral fissure. Processes that shape the clonal patchwork are both passive and active, intrinsic and extrinsic. Certain features of the clonal architecture of the retina, such as the size differences of clones are primarily passive responses to extrinsic forces on progenitor cells and their progeny. The fifteen-fold range in the size of cohorts is not due to intrinsic differences in the proliferative capacity of individual progenitor cells, but is due to the extent of cell movement and mixing at early stages of development. In contrast, active or intrinsic processes are illustrated by the partial (and still controversial) restriction of retinal progenitors, the possible clonal differences between ganglion cells with crossed and uncrossed projections, and the consistent differences in ratios of albino and pigmented genotypes in peripheral and central retina.

The annexins are a group of structurally related proteins implicated in a number of cellular processes, including growth, membrane fusion, and the effects of glucocorticoids on cellular physiology, signal transduction, and regulation of activities of phospholipase A2. Though their exact role in cellular physiology is not clear, their properties make them candidate proteins for signal transduction pathways by which growth factors and glucocorticoids modulate development of the palate. We have determined the exact cellular location and development expression of various annexins in the embryonic murine palate as a first step in assessing their developmental function. Western blot analysis revealed an increased accumulation of selected annexins in elevated palates compared to vertical (unelevated) ones. This was particularly striking for lipocortin I1 (annexin I), whose mRNA accumulated as well. Lipocortin I was expressed primarily in the apical portion of the palatal epithelium at early stages of development, but throughout the epithelium at later stages. Also, there was increased immunoreactivity for lipocortin I in the mesenchyme as development proceeded. Immunoreactivity for the endonexins (annexins IV and V) was found in the palatal epithelium and mesenchyme, whereas immunoreactivity for the 67-kDa calelectrin (annexin VI) was found only in the mesenchyme. Treatment of pregnant A/J strain mice with a cleft-palate inducing regimen of dexamethasone stimulated accumulation of lipocortin I protein and mRNA, but not lipocortin II (annexin II) protein. In contrast, the same regimen of dexamethasone did not affect levels of lipocortin I protein in palates of the glucocorticoid-less sensitive C57BL/6J strain mouse embryo. These data permit the suggestion that lipocortin I plays some critical, but as yet undefined, role in modulating ontogeny of the murine palate.

Functionally hemidecorticated rats were trained with the right hemisphere to go right and 24 hr later with the left hemisphere to go left in a simple T-maze. In 5 free choice (FC) trials performed with intact brain on Day 3 equilibration of the right and left turns (40% FC left) was found when 9 10 avoidance + 30 overtraining trials to the right were followed by 3 3 escapes to the left. Control groups trained only in the first or the second habit chose the left arm in 15% and 73%, respectively, whereas intact rats learning the two tasks sequentially displayed a marked reversal (83% FC left). When rats trained under the above equilibrated choice conditions were subjected with intact brain two hr before the second hemidecorticate training to a strong emotional experience (20 min swimming), the percentage of left choices was significantly increased on Day 3 (70% FC left). Swimming neither interfered with retention of the isolated first engram (20% FC left) nor improved the acquisition of the isolated second engram (65% FC left), but when inserted between two lateralized learning sessions with opposite hemispheres it increased the weight of the second experience to the level found in reversal learning. Similar results were obtained with a water T-maze when using foot shocks (30 min) as reference. A hypothetical model is proposed explaining the absence of relative time labelling of lateralized engrams and the possibility to restore it by the bilaterally recorded reference event, bridging the gap in the hemispheric memory records.

Mice homozygous for the autosomal recessive mutation wasted (wst/wst) undergo a progressive wasting beginning at the third week of postnatal life, when body weight declines in the mutants. The wst/wst mice do not survive past 30 days of age. The present report describes histologic and functional abnormalities in a longitudinal analysis (17 to 29 days postpartum) of wst/wst mice. In addition to a marked age-dependent decline in wst/wst body weight as well as spleen and thymus wet weight to body weight ratios, we have observed a significant decline in spleen and thymus cell number in these organs, compared with phenotypically normal (+/+ or +/wst) littermates. Histologic analysis of the wst/wst thymus revealed marked cortical pyknosis at 23 days of age and significant cortical depletion by 26 days postpartum. The wst/wst spleen at 23 days of age and later was characterized by a marked reduction in the content of red pulp. Lymphoproliferative responsiveness to Con A was markedly altered in the wst/wst thymus and spleen, in an age-dependent fashion, compared with normal littermates. The wst/wst spleen LPS responsiveness was also markedly altered in an age-dependent fashion. Hypotheses are presented concerning the possible site(s) of gene action in the wst/wst mutant which may mediate the observed morphologic and functional abnormalities.