Nerve terminals of squid photoreceptor neurons contain a heterogeneous population of mRNAs and translate a transfected reporter mRNA

Abstract

It is now well established that the distal structural/functional domains of the neuron contain 2a diverse population of mRNAs that program the local synthesis of protein. However, there is still a paucity of information on the composition and function of these mRNA populations in the adult nervous system. To generate empirically, hypotheses regarding the function of the local protein synthetic system, we have compared the mRNAs present in the squid giant axon and its parental cell bodies using differential mRNA display as an unbiased screen. The results of this screen facilitated the identification of 31 mRNAs that encoded cytoskeletal proteins, translation factors, ribosomal proteins, molecular motors, metabolic enzymes, nuclear-encoded mitochondrial mRNAs, and a molecular chaperone. Results of cell fractionation and RT-PCR analyses established that several of these mRNAs were present in polysomes present in the presynaptic nerve terminal of photoreceptor neurons, indicating that these mRNAs were being actively translated. Findings derived from in vitro transfection studies established that these isolated nerve terminals had the ability to translate a heterologous reporter mRNA. Based upon these data, it is hypothesized that the local protein synthetic system plays an important role in the maintenance/remodelling of the cytoarchitecture of the axon and nerve terminal, maintenance of the axon transport and mRNA translation systems, as well as contributing to the viability and function of the local mitochondria.

Transcriptome analysis of embryonic and adult sensory axons reveals changes in mRNA repertoire localization

“…These data show that axons isolated from embryonic and adult rat DRG neurons are enriched in protein synthesis, mitochondrial, and neurite growth-related mRNAs that appear to be common critical elements found in other types of axons (Chun et al 1995(Chun et al , 1997Bassell et al 1998;Eng et al 1999;Zheng et al 2001;Gioio et al 2004;Willis et al 2005Willis et al , 2007Wu et al 2005;Leung et al 2006;Aschrafi et al 2008Aschrafi et al , 2010Taylor et al 2009;Andreassi et al 2010). …”

“…Examples of cytoskeletal mRNAs were several ''core'' cytoskeletal components. These included transcripts for isoforms of Tubulin (i.e., Tubb3), several microtubule associated proteins (i.e., Map1B), microtubule stabilizing proteins (i.e., Clasp2), and regulators of actin dynamics (i.e., Cfl1, Pfn2, Dbn1), several of which have also been reported in different axon types including axons from other species (Chun et al 1997;Gioio et al 2004;Willis et al 2005;Taylor et al 2009). Within the transport of vesicles category we detected mRNAs encoding anterograde and retrograde microtubule associated motor proteins (i.e., Kif5A, Dctn2) (Hirokawa et al 2009).…”

Caltubin, a Novel Molluscan Tubulin-Interacting Protein, Promotes Axonal Growth and Attenuates Axonal Degeneration of Rodent Neurons

“…Local protein synthesis is one of the crucial mechanisms regulating neurite outgrowth, growth cone behavior, and axonal regeneration (Gumy et al, 2010). Whereas the exact downstream mechanisms by which local protein synthesis regulates axon growth remain unclear, most mRNAs that are identified in axonal growth cones appear to be structural proteins in both invertebrates (Plunet et al, 2002;Gioio et al, 2004) and in vertebrates (Willis et al, 2005;Hengst et al, 2009), and translational regulation of these proteins occurs during axon regeneration (Twiss et al, 2000). For instance, stimulus-driven axonal growth is dependent on local translation of the cytoskeleton regulator PAR (Hengst et al, 2009), and inhibition of local translation of the actin regulating protein ␤-thymosin enhances rates of neurite outgrowth (van Kesteren et al, 2006).…”

Local Gene Expression in Axons and Nerve Endings: The Glia-Neuron Unit

“…RT-PCR analyses of synaptosomal polysomes have led to the identification of mRNAs coding for cytoskeletal and ribosomal proteins, translation factors and, most notably, mitochondrial proteins encoded by nuclear DNA (110,111). The association of these mRNAs with purified polysomes indicates that the corresponding proteins are synthesized in presynaptic synaptosomes.…”