N-syndecan and HB-GAM (heparin-binding growth-associated molecule) associate with early axonal tracts in the rat brain.
Heparin-Binding Growth-Associated Molecule (HB-GAM)/pleiotrophin is an 18 kDa extracellular matrix- and cell-surface-associated protein shown to enhance neurite outgrowth of perinatal forebrain neurones in vitro. The heparan sulphate proteoglycan N-syndecan (Raulo et al., 1994) has been isolated as a receptor/coreceptor for the HB-GAM. We have investigated, whether HB-GAM and N-syndecan could have a similar role in neurite outgrowth and axon guidance in early axonal tracts of brain. In the present study N-syndecan was found to be spatiotemporally associated with the developing axonal tracts already on embryonic day 9 in rat, as revealed by coexpression with class III beta-tubulin, which is one of the earliest neuronal markers (Easter et al., 1993; Brittis et al., 1995). Later, N-syndecan and HB-GAM were detected in the first afferent serotonergic projections arising from the pontine raphe nuclei. The expression pattern of HB-GAM peaked in the developing rhombencephalon at embryonic stage (E) 13-14. At the same time, N-syndecan was expressed in the developing raphe neurones growing neurites towards the diencephalon along HB-GAM immunoreactive pathways. When rhombencephalic neurones were cultured on decreasing concentrations of substrate-bound HB-GAM, E13 neurones showed a significantly better neurite outgrowth response than E11, E16 or E18 neurones. The neurite outgrowth of raphe neurones in vitro was inhibited by adding soluble heparin or N-syndecan into the culture medium, whereas addition of chondroitin sulphate had no effect. In a simple pathway assay, E13 raphe neurones selectively preferred attaching and growing neurites on pathways containing HB-GAM as compared with regions containing either laminin or fibronectin alone. Our results suggest that HB-GAM may function as a developmentally regulated cue for rhombencephalic neurones that possess N-syndecan on their cell membrane.
Kinnunen
A
A
Institute of Biomedicine, Department of Anatomy, University of Helsinki, Finland.
Kinnunen
T
T
Kaksonen
M
M
Nolo
R
R
Panula
P
P
Rauvala
H
H
D000818:Animals; D001369:Axons / Q000378:metabolism*; D001923:Brain Chemistry / Q000502:physiology*; D002352:Carrier Proteins / Q000378:metabolism*; D002478:Cells, Cultured; D016207:Cytokines / Q000378:metabolism*; D007150:Immunohistochemistry; D017403:In Situ Hybridization; D008562:Membrane Glycoproteins / Q000378:metabolism*; D009419:Nerve Tissue Proteins / Q000378:metabolism*; D011509:Proteoglycans / Q000378:metabolism*; D011903:Raphe Nuclei / Q000166:cytology / Q000378:metabolism; D051381:Rats; D017208:Rats, Wistar; D017468:Receptors, Fibroblast Growth Factor / Q000378:metabolism*; D012249:Rhombencephalon / Q000166:cytology / Q000378:metabolism; D053670:Syndecan-3; D014404:Tubulin / Q000378:metabolism
D002352:Carrier Proteins; D016207:Cytokines; D008562:Membrane Glycoproteins; D009419:Nerve Tissue Proteins; D011509:Proteoglycans; D017468:Receptors, Fibroblast Growth Factor; C508303:Sdc3 protein, rat; D053670:Syndecan-3; D014404:Tubulin; C066845:pleiotrophin