Nisson Schechter, Ph.D.
of Psychiatry and Behavioral Science
Stony Brook, NY 11794-5215
Office telephone: 631-444-1368
Molecular and Cell Biology of Nerve Development, Growth, and Regeneration
in the Zebrafish Visual Pathway.
The research focus of this laboratory is to discover
proteins which regulate and support the development and growth of neurons.
As our initial model system, we used the visual pathway of goldfish which
displays continuous growth and development throughout life. In addition,
functional regeneration of the goldfish optic nerve occurs after injury.
This is important clinically because functional regeneration does not
occur in the mammalian central nervous system. More 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 IF 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 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. A related project is investigating the role of a ubiquitin-like
conjugating enzyme, Ubc9, in the transport of Vsx-1 and Vsx-2 to the nucleus.
All of our experiments utilize the techniques of molecular and cell biology
to determine how specific homeobox transcription factors regulate cell fate
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