Synapsin and synaptic vesicle protein expression during embryonicand post-natal lens fiber cell differentiation

[摘要] Purpose: Reorganization of cytoskeleton and membrane biogenesis aredynamically coordinated during lens fiber cell differentiation anddevelopment to produce an organ with precise dimensions and opticalproperties. Cargo vesicle trafficking is fundamental to cell elongationand has also been implicated in degenerative disease mechanisms.Alzheimer precursor protein (AβPP) acts with kinesin, synapsin, andsynaptic vesicle proteins to mediate cargo vesicle transport andmembrane fusion in neurons. In our previous studies we demonstrated thatAβPP is also a key element in lens fiber cell formation, and inearly-onset cataract that occurs along with early-onset Alzheimerdisease in Down syndrome. In the present study we examine lensexpression and regulation of a complement of genes associated with cargoand synaptic vesicle transport in neurons.Methods: RT-PCR, immunoblot, and immunohistochemical methods wereused to characterize expression of AβPP and kinesin associatedmotor proteins, synapsins, and synaptic vesicle proteins in mouse andrat embryonic, post-natal, and adult lenses. Phospho-specificanti-synapsin antibodies were used to determine the distributions ofsite-1 phosphorylated and dephosphorylated synapsin protein.Results: We demonstrate that a substantial complement of cargo andsynaptic vesicle proteins involved in AβPP mediated vesicletransport are expressed in lenses along the anterior-posterior axis offiber cells in embryonic and adult lenses, consistent with vesicles,actin filaments, and neuron-like arrangement of microtubules in lensesshown by others. We identify temporal regulation of synapsins I, II, andIII during embryonic and post-natal lens development consistent withtheir roles in neurons. Regulation of vesicle cytoskeleton attachment,actin polymerization, and the capacity to stimulate cell differentiationby synapsins are governed in large part by phosphorylation at aconserved Ser9 residue (site-1). We demonstrate discretedistributions of Ser9 phospho- and dephospho-synapsins along theaxial length of rapidly elongating embryonic lens fiber cells, anddecreased levels of site-1 phosphorylated synapsins in adult lenses.Conclusions: The present findings demonstrate several fundamentalparallels between lens and neuron vesicle trafficking cell biology anddevelopment, and suggest that more extensive AβPP related vesicletrafficking disease mechanisms may be shared by lens and brain.

[学科分类] 生物化学/生物物理