Retinal horizontal cells lacking Rb1 sustain persistent DNA damage and survive as polyploid giant cells.

The retinoblastoma tumor susceptibility gene, Rb1, is a key regulator of the cell cycle, and mutations in this gene have been found in many human cancers. Prior studies showed that retina-specific knockout of Rb1 in the mouse results in the formation of abnormally large horizontal cells, but the development, fate, and genomic status of these cells remain unknown. In this study, we conditionally inactivate Rb1 in early retinal progenitors and show that the loss of Rb1 leads to the rapid degeneration of most retinal cells except horizontal cells, which persist as giant cells with aberrant centrosome content, DNA damage, and polyploidy/aneuploidy.

GAP-43 is critical for normal targeting of thalamocortical and corticothalamic, but not trigeminothalamic axons in the whisker barrel system.

Mice lacking the growth-associated protein GAP-43 (KO) show disrupted cortical topography and no barrels. Whisker-related patterns of cells are normal in the KO brainstem trigeminal complex (BSTC), while the pattern in KO ventrobasal thalamus (VB) is somewhat compromised. To better understand the basis for VB and cortical abnormalities, we used small placements of DiI to trace axonal projections between BSTC, VB, and barrel cortex in wildtype (WT) and GAP-43 KO mice.

Discovery of an oncogenic activity in p27Kip1 that causes stem cell expansion and a multiple tumor phenotype.

The cell cycle inhibitor p27Kip1 also has cyclin-cyclin-dependent kinase (CDK)-independent functions. To investigate the significance of these functions in vivo, we generated a knock-in mouse in which four amino acid substitutions in the cdkn1b gene product prevent its interaction with cyclins and CDKs (p27CK-). In striking contrast to complete deletion of the cdkn1b gene, which causes spontaneous tumorigenesis only in the pituitary, the p27CK- protein dominantly caused hyperplastic lesions and tumors in multiple organs, including the lung, retina, pituitary, ovary, adrenals, spleen, and lymphomas.

Preparation and square wave electroporation of retinal explant cultures.

This protocol details organotypic cultures of developing mouse, monkey and human retinas, which can be maintained for up to 2 weeks. Intact retinas are placed on polycarbonate filters floating on explant culture medium and fed every day with previously prepared retinal conditioned medium. Developing mouse retinas from E12.

Inactivation of the p53 pathway in retinoblastoma.

Most human tumours have genetic mutations in their Rb and p53 pathways, but retinoblastoma is thought to be an exception. Studies suggest that retinoblastomas, which initiate with mutations in the gene retinoblastoma 1 (RB1), bypass the p53 pathway because they arise from intrinsically death-resistant cells during retinal development. In contrast to this prevailing theory, here we show that the tumour surveillance pathway mediated by Arf, MDM2, MDMX and p53 is activated after loss of RB1 during retinogenesis.

Mosaic deletion of Rb arrests rod differentiation and stimulates ectopic synaptogenesis in the mouse retina.

The retinoblastoma gene (Rb) regulates neural progenitor cell proliferation and cell fate specification and differentiation. For the developing mouse retina, two distinct functions of Rb have been described: regulation of retinal progenitor cell proliferation and rod photoreceptor development. Cells that would normally become rods fail to mature and remain as immature cells in the outer nuclear layer in the adult.

Compensation by tumor suppressor genes during retinal development in mice and humans.

Background: The RB1 gene was the first tumor suppressor gene cloned from humans by studying genetic lesions in families with retinoblastoma. Children who inherit one defective copy of the RB1 gene have an increased susceptibility to retinoblastoma. Several years after the identification of the human RB1 gene, a targeted deletion of Rb was generated in mice.

Regulation of proliferation during central nervous system development.

The retina is one of the best-characterized regions of the central nervous system (CNS) and has served as a model for many of the principles that now form the foundation for CNS development. In the past several years, a number of advances have been made in our understanding of the coordination of proliferation and cell fate specification during retinal development. In this review, we will draw on findings from studies of the retina and highlight similarities and differences in other regions in the CNS, namely the cerebellum and cortex.

Retinal degeneration in Aipl1-deficient mice: a new genetic model of Leber congenital amaurosis.

Leber congenital amaurosis (LCA) is the most severe inherited retinopathy, with the earliest age of onset. Because this currently incurable disease is present from birth and is a relatively rare disorder, the development of animal models that closely resemble the phenotype in patients is especially important. Our previous genetic analyses of LCA patients identified mutations in the aryl-hydrocarbon interacting protein-like 1 (AIPL1) gene.

Developmental defects in Rb-deficient retinae.

We recently found that the Rb protein is important for the regulation of retinal progenitor cell proliferation and rod photoreceptor development in the mouse retina. These two functions are separate for Rb and in this study we further characterize the role of Rb in retinal development. At postnatal day 12 in the retinae of Chx10-Cre;RbLox/- mice, immature cells are found in the outer nuclear layer where rods normally are differentiating.

GAP-43 is critical for normal development of the serotonergic innervation in forebrain.

Serotonergic (5-HT) axons from the raphe nuclei are among the earliest afferents to innervate the developing forebrain. The present study examined whether GAP-43, a growth-associated protein expressed on growing 5-HT axons, is necessary for normal 5-HT axonal outgrowth and terminal arborization during the perinatal period. We found a nearly complete failure of 5-HT immunoreactive axons to innervate the cortex and hippocampus in GAP-43-null (GAP43-/-) mice.

Growth-associated protein-43 is required for commissural axon guidance in the developing vertebrate nervous system.

Growth-associated protein-43 (GAP-43) is a major growth cone protein whose phosphorylation by PKC in response to extracellular guidance cues can regulate F-actin behavior. Here we show that 100% of homozygote GAP-43 (-/-) mice failed to form the anterior commissure (AC), hippocampal commissure (HC), and corpus callosum (CC) in vivo. Instead, although midline fusion was normal, selective fasciculation between commissural axons was inhibited, and TAG-1-labeled axons tangled bilaterally into Probst's bundles.