Pharmacological Sciences

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.