Temporal changes in beta-tubulin and neurofilament mRNA levels after transection of adult rat retinal ganglion cell axons in the optic nerve

Abstract

Axons of adult mammalian retinal ganglion cells (RGCs) do not regenerate spontaneously after injury in the optic nerve and show a persistent decrease in the rate of transport of tubulin and neurofilament proteins. To investigate further the expression of cytoskeletal proteins in these axotomized CNS neurons, mRNA levels of beta-tubulin and the 150 kDa neurofilament subunit (NF-M) were measured after interrupting the optic nerve 9 mm from the eye. Northern blots of RNA extracted from whole retinas after optic nerve transection showed that the total level of both of these mRNAs fell after injury. To determine if this decrease was a result of the death of axotomized RGCs or reflected changes in individual neurons, RNA probes were hybridized to radial cryostat sections of normal and axotomized retinas from 1 d to 6 months after injury. Grain counts revealed two trends of tubulin expression in RGCs. An early increase in tubulin mRNAs in the axotomized RGCs was followed by a later decrease. Such an increase in tubulin mRNA levels has been correlated with regenerative growth in other neurons. By 1 week after injury, the beta-tubulin mRNA levels decreased to 70% of the control value. Moreover, the time of this fall coincided with the onset of a marked slowing of cytoskeletal transport that follows injury in the optic nerve. In contrast, NF-M mRNA levels dropped immediately after axotomy, and remained at 80% of the control level. It is suggested that the transient increase in tubulin mRNAs may reflect an early regenerative response whose persistence depends on further growth cone interactions with the substrate.

Application of Rho Antagonist to Neuronal Cell Bodies Promotes Neurite Growth in Compartmented Cultures and Regeneration of Retinal Ganglion Cell Axons in the Optic Nerve of Adult Rats

“…The position of the front was determined as the segment preceding the one in which the protein density dropped to 10% of its highest value for that animal. The expression level of NF-M is 85% of controls 2 weeks after an intracranial crush of the optic nerve (McKerracher et al, 1993). NF-M lanes of an autoradiograph were scanned for densitometry using an Epson perfection 1200U scanner, transferred to Adobe Photoshop 6.0 (Adobe Systems, San Jose, CA), and the images were analyzed with the densitometry IQ MAC 1.2 software (Molecular Dynamics, Sunnyvale, CA).…”

Recovery of Neurofilament Expression Selectively in Regenerating Reticulospinal Neurons

“…In goldfish, the expression of mRNA for the NF ON-1 increased during optic nerve regeneration (Tesser et al, 1986;Glasgow et al, 1994). On the other hand, NF mRNA, protein synthesis, and transport are reduced in mammalian peripheral (Hoffman et al, 1985;Goldstein et al, 1988;Oblinger and Lasek, 1988) and central neurons (Mikucki and Oblinger, 1991;Tetzlaff et al, 1991;Hoffman et al, 1993;McKerracher et al, 1993a) after axotomy. The changes are reversed in peripheral neurons only after regenerating axons reach their targets (Hoffman et al, 1985;Hoffman and Cleveland, 1988;Muma et al, 1990;Wong and Oblinger, 1990b), and they persist if regeneration is prevented (Tetzlaff et al, 1988;Jiang et al, 1994).…”

“…Other studies suggest that after axotomy, NF mRNA expression is influenced by the residual axon volume. When rat optic nerve was transected 9 mm from the eye, NF-M message levels in retina were reduced by 30% (McKerracher et al, 1993a), whereas transection 0.5 mm from the retina induced a 50% reduction in middle molecular weight NF (NF-M) mRNA (McKerracher et al, 1993b). Despite reduced NF message levels, NF transport in regenerating retinal ganglion cell axons was twice that of intact axons (McKerracher et al, 1990).…”

Sprouting, regeneration and circuit formation in the injured spinal cord: factors and activity

“…Among them, L1, c-Jun and c-Fos are cytoskeletal proteins Chaisuksunt et al 2000a,b), and the 43 kDa is a growthassociated protein (GAP-43) (McKerracher et al 1993;Tetzlaff et al 1994;Caroni 1997;Mason et al 2003;Wintzer et al 2004). These genes are typically expressed in developing neurons (Skene 1989;Hunt & Mantyh 2001) but less in most adult CNS neurons except in regions known for their plastic potential (Benowitz & Perrone-Bizzozero 1991).…”