Distribution of transcript and protein isoforms of the synaptic glycoprotein neuroplastin in rat retina.
OBJECTIVE
To examine the expression and localization of the neuroplastins (np), two synapse-enriched members of the immunoglobulin (Ig) superfamily of cell-adhesion molecules, in the developing and adult retina and optic nerve.


METHODS
Expressions of the two isoforms np55 and np65 and carboxyl-terminal splice variants were investigated by immunocytochemistry, Western blot analysis, RT-PCR, and in situ hybridization.


RESULTS
Immunoreactivity for both neuroplastins was confined to the two synaptic layers of the retina: the inner (IPL) and outer plexiform layer (OPL). Significant overlap was found in staining at synaptic structures with synaptophysin. A large proportion of immunoreactivity for both isoforms, however, was of perisynaptic origin. In situ hybridization studies were suggestive of a pre- and postsynaptic localization of np65 in the OPL. Transcripts for np55 were already present at birth in the inner retina, but the hybridization signals increased during postnatal development. Np65 transcripts and immunosignals appeared at later developmental ages, concomitant with synapse formation in the OPL. Several C-terminal neuroplastin cDNA clones harbor an insert of 12 bp, coding for four amino acids (DDEP) in the intracellular domain of neuroplastins. Splice isoforms containing the insert exhibited a developmental expression pattern similar to that of np55; however, both neuroplastins could harbor the C-terminal insert. Neuroplastins were also detected in optic nerve homogenates. RT-PCR and blockade of axonal transport by nerve crush confirmed transcript and protein expression in optic nerve tissue.


CONCLUSIONS
The findings suggest a role for neuroplastins in cell adhesion in the plexiform layers during histogenesis, as well as in maintenance of connections between specific cellular structures.
Kreutz
M R
MR
AG Molecular Mechanisms of Plasticity, Department of Neurochemistry/Molecular Biology, Leibniz Institute for Neurobiology, Brenneckstr. 6, 39118 Magdeburg, Germany. kreutz@ifn-magdeburg.de
Langnaese
K
K
Dieterich
D C
DC
Seidenbecher
C I
CI
Zuschratter
W
W
Beesley
P W
PW
Gundelfinger
E D
ED
D000818:Animals; D015153:Blotting, Western; D017931:DNA Primers / Q000737:chemistry; D019084:Fluorescent Antibody Technique, Indirect; D015870:Gene Expression; D007136:Immunoglobulins / Q000235:genetics* / Q000378:metabolism; D017403:In Situ Hybridization; D008297:Male; D008562:Membrane Glycoproteins / Q000235:genetics* / Q000378:metabolism; D009419:Nerve Tissue Proteins / Q000235:genetics* / Q000378:metabolism; D009900:Optic Nerve / Q000378:metabolism; D020033:Protein Isoforms; D012333:RNA, Messenger / Q000378:metabolism; D051381:Rats; D017207:Rats, Sprague-Dawley; D012160:Retina / Q000254:growth & development / Q000378:metabolism*; D020133:Reverse Transcriptase Polymerase Chain Reaction
D017931:DNA Primers; D007136:Immunoglobulins; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; C548934:Nptn protein, rat; D020033:Protein Isoforms; D012333:RNA, Messenger; C103658:synaptic glycoprotein gp65