Molecular Development of the Optic Nerve and Regeneration after Injury

Ph.D., Western Michigan University, 1971
Postdoctoral, University of Cincinnati Medical School,
Weizmann Institute of Science, Israel

The research goals of this laboratory are to discover proteins which regulate and support the development and growth of neurons. We initially used the visual pathway of goldfish, which displays continuous growth and development throughout life and shows functional regeneration of the optic nerve after injury. This is important clinically because functional regeneration does not occur in the mammalian central nervous system. Recently, we shifted our research focus to the zebrafish model system. Although zebrafish are physiologically similar to goldfish, proteins that are crucial to development can be studied in the transparent zebrafish embryos. Furthermore, the zebrafish is amenable to genetic manipulation. Thus, the zebrafish allows us to combine the techniques of molecular biology with those of cell biology to discover how specific proteins regulate and support neurogenesis.

Plasticin and gefiltin are two intermediate filament (IF) proteins that we discovered in goldfish and have subsequently characterized in zebrafish. The expression of these proteins is correlated with the development, growth and regeneration of the optic nerve. Furthermore, plasticin and gefiltin are structurally related to IF proteins that are expressed in the mammalian visual pathway during development. Since plasticin is expressed in newer retinal ganglion cells and is seen early in response to injury, we hypothesize that plasticin supports the initial growth phase of the optic nerve. On the other hand, gefiltin is expressed in older cells and during later phases of regeneration. Thus, we hypothesize that it is more essential to the formation of terminals of the retinal projections. Currently, we are using cultured cells to determine the impact of plasticin and gefiltin expression on the assembly of the intermediate filament network. In addition, we are using zebrafish embryos to determine the regulatory mechanisms by which a given cell type (such as retinal ganglion cells) can trigger the sequential expression of these structurally similar proteins from the same super gene family.

We have also discovered two homeobox genes, Vsx-1 and Vsx-2, that were originally cloned from adult goldfish retina. These proteins are members of the paired-like:CVC subclass of homeobox genes. Paired-like:CVC proteins contain a 54-58 amino acid region, termed the CVC domain, which is adjacent to the C-terminus of the homeodomain. The expression of these transcription factors is linked to retinal development. In addition, a mutation in the mouse homologue of Vsx-2 results in ocular retardation.

Histological analysis in goldfish and zebrafish suggests roles for Vsx-1 and Vsx-2 in the differentiation of bipolar cells and in their stabilization within the laminated retina. Initially, Vsx-1 and Vsx-2 are expressed in a complementary fashion, but later their expression patterns become superimposed. This sequential change in expression pattern suggests that these similar transcription factors may be recruited for partially overlapping, but distinct, functions during retinal development. This dynamic expression of Vsx-1 and Vsx-2 suggests that these transcription factors must have a rapid turnover to permit precise regulation during development. One mechanism by which this might occur is via the ubiquitin/ proteasome pathway. Current research is determining the roles of the CVC domain and putative phosphorylation sites in the ubiquitination of Vsx-1 and Vsx-2.

Selected Publications

• Kurtzman Aaron L; Gregori Luisa; Haas Arthur L; Schechter Nisson. Ubiquitination and degradation of the zebrafish paired-like homeobox protein Vsx-1. Journal of Neurochemistry. 75(1). July, 2000. 48-55.
  
  
• Canger Anthony K; Passini Marco A; Asch William S; Leake Devin; Zafonte Brian T; Glasgow Eric; Schechter Nisson. Restricted expression of the neuronal intermediate filament protein plasticin during zebrafish development. Journal of Comparative Neurology. 399(4). Oct. 5, 1998. 561-572.
  
  
• Asch William S; Leake Devin; Canger Anthony K; Passini Marco A; Argenton Francesco; Schechter Nisson. Cloning of zebrafish neurofilament cDNAs for plasticin and gelfitin: Increased mRNA expression in ganglion cells after optic nerve injury. Journal of Neurochemistry. 71(1). July, 1998. 20-32.
  
  
• Passini Marco A; Raymond Pamela A; Schechter Nisson. Vsx-2, a gene encoding a paired-type homeodomain, is expressed in the retina, hindbrain, and spinal cord during goldfish embryogenesis. Brain Research. Developmental Brain Research. 109(2). Aug. 8, 1998. 129-135.
  
  
• Passini Marco A; Kurtzman Aaron L; Canger Anthony K; Asch William S; Wray Gregory A; Raymond Pamela A; Schechter Nisson. Cloning of zebrafish vsx1: Expression of a paired-like homeobox gene during CNS development. Developmental Genetics. 23(2). 1998. 128-141.
  
  
• Levine Edward M; Passini Marco; Hitchcock Peter F; Glasgow Eric; Schechter Nisson. Vsx-1 and Vsx-2: Two Chx10-like homeobox genes expressed in overlapping domains in the adult goldfish retina. Journal of Comparative Neurology. 387(3). 1997. 439-448.
  
  
• Glasgow Eric; Druger Robert K; Fuchs Chana; Lane William S; Schechter Nisson. Molecular cloning of gefiltin (ON-1): Serial expression of two new neurofilament mRNAs during optic nerve regeneration. EMBO (European Molecular Biology Organization) Journal. 13(2). 1994. 297-305.
  
  
• Fuchs Chana; Glasgow Eric; Hitchcock Peter F; Schechter Nisson. Plasticin, a newly identified neurofilament protein, is preferentially expressed in young retinal ganglion cells of adult goldfish. Journal of Comparative Neurology. 350(3). 1994. 452-462.
  
  
• Levine Edward M; Hitchcock Peter F; Glasgow Eric; Schechter Nisson. Restricted expression of a new paired-class homeobox gene in normal and regenerating adult goldfish retina. Journal of Comparative Neurology. 348(4). 1994. 596-606.
  
  
• Levine Edward M; Schechter Nisson [a]. Homeobox genes are expressed in the retina and brain of adult goldfish. Proc. of the Nat'l Acad. of Sci. of the USA. 90(7). 1993. 2729-2733.