| 摘要 |
Distinct cDNAs encoding six cysteine-rich domain-NRGs and four glial growth factor isoforms were identified and sequenced. Additional heterogeneity is found in the EGF-like (alpha- and beta-isoforms) and carboxy terminal (a and b variant) regions of CRD-NRGs. Furthermore, the predicted GGF proteins contain glycosylation domains previously found only in mesenchymal NRGs. GGF mRNAs accumulate in axotomized nerve, a subpopulation of DRG neurons and most spinal cord motoneurons. CRD-NRGs, however, are undetectable in injured nerve except by RT-PCR. In contrast, the majority of DRG and spinal cord motor neurons express CRD-NRGs, with a beta1 isoform being most abundant and at least some of these proteins are secreted in a form capable of activating erbB receptors. Thus, GGF and CRD-NRG subfamilies are more structurally diverse than previously appreciated. NRG actions during Wallerian degeneration may be modulated by the action of distinct splice variants. |
