Sa. Mahoney et al., Stabilization of neurites in cerebellar granule cells by transglutaminase activity: Identification of midkine and galectin-3 as substrates, NEUROSCIENC, 101(1), 2000, pp. 141-155
The formation of covalent isopeptide cross-links between cell surface prote
in molecules by the enzyme transglutaminase C influences cell adhesion and
morphology. Retinoid-inducible cross-linking activity associated with this
enzyme is present in the developing rat cerebellar cortex [Perry M. J. M. e
t nl. (1995) Neuroscience 65, 1063-1076]. A monoclonal antibody was used to
localize transglutaminase C to granule neurons in the developing cerebella
r cortex. The enzyme was inducible by retinoic acid both in granule neurons
cultured from postnatal rat cerebellar cortex and in cells of the embryoni
c dorsal rhombic lip, which contain granule neuron precursors. A possible b
iological function for transglutaminase activity was investigated in living
granule neurons, cultured on a biomatrix substratum, studied by time-lapse
cinematographic analysis using the transglutaminase inactivator RS-48373-0
07. Inhibition of cross-linking activity did not influence the number of ne
urites formed by granule neurons, but caused the destabilization of neurite
s during the initial outgrowth period, seen as an increase in the number of
growth cone retractions and the onset of premature axon collateral formati
on (bifurcation). Inactivation of cross-linking activity prevented the form
ation of fascicles between neurites only when cells were cultured on a biom
atrix surface. Two glial proteins involved in cell-extracellular matrix int
eractions, midkine and galectin-3, were identified as putative substrates f
or granule neuron transglutaminase.
The results suggest that covalent cross-link formation by transglutaminase
C or a related enzyme generates multimeric molecular forms of glial-derived
proteins, and plays a role in stabilizing newly formed neurites. A possibl
e non-pathological role for transglutaminase in the control of axon collate
ral branching by developing granule neurons in the cerebellar cortex is dis
cussed.