Neurons Expressing the Highest Levels of γ-Synuclein Are Unaffected by Targeted Inactivation of the Gene

Abstract

Homologous recombination in ES cells was employed to generate mice with targeted deletion of the first three exons of the ␥-synuclein gene. Complete inactivation of gene expression in null mutant mice was confirmed on the mRNA and protein levels. Null mutant mice are viable, are fertile, and do not display evident phenotypical abnormalities. The effects of ␥-synuclein deficiency on motor and peripheral sensory neurons were studied by various methods in vivo and in vitro. These two types of neurons were selected because they both express high levels of ␥-synuclein from the early stages of mouse embryonic development but later in the development they display different patterns of intracellular compartmentalization of the protein. We found no difference in the number of neurons between wild-type and null mutant animals in several brain stem motor nuclei, in lumbar dorsal root ganglia, and in the trigeminal ganglion. The survival of ␥-synuclein-deficient trigeminal neurons in various culture conditions was not different from that of wild-type neurons. There was no difference in the numbers of myelinated and nonmyelinated fibers in the saphenous nerves of these animals, and sensory reflex thresholds were also intact in ␥-synuclein null mutant mice. Nerve injury led to similar changes in sensory function in wild-type and mutant mice. Taken together, our data suggest that like ␣-synuclein, ␥-synuclein is dispensable for the development and function of the nervous system. Several neurodegenerative diseases have been recently coalesced into a distinct group named synucleinopathies (12,16,20,53). Although they are diverse in symptoms and clinical signs, these diseases share a common histopathological feature, i.e., formation of large intracellular inclusions whose principal component is an aggregated small protein, ␣-synuclein. Neither the normal cellular function of ␣-synuclein nor the exact mechanism of its involvement in neurodegeneration is clearly understood; possible scenarios are discussed in many recent reviews (see, for example, references 10, 28, 33, 34, and 43). Even less clear are the normal functions and roles in neurodegeneration of the other two members of the synuclein family. Both ␤-synuclein/PNP14 (24, 35) and ␥-synuclein/BCSG1/persyn (7, 26, 29) have a very high degree of amino acid similarity with ␣-synuclein within the N-terminal KTK repeat region of the protein molecule, and this is reflected in such common features of synucleins as a native unfolded state in physiological solutions, reversible binding to lipid vesicles, and localization in presynaptic terminals (13,25,31). However, the C-terminal regions of synucleins, although all highly acidic, are rather different (7, 29, 52). It is perhaps this structural diversity that leads to differences in the behavior of synucleins in vitro and in various in vivo model systems. Consistent with the finding that ␤-synuclein and ␥-synuclein are much less fibrillogenic than ␣-synuclein (4, 47, 55), aggregates of these two proteins are not constituents of Lewy b...

Localization of Synucleins in the Mammalian Cochlea

“…Our studies show no phenotypic or histological differences in the inner ears of the wild-type vs. the knockout mice, while ABR thresholds and otoacoustic emissions also are unchanged in the knockout mouse through P21. This follows prior studies on this same mouse, in which no difference was observed in the number of neurons between wild-type and null mutant animals in several brain stem motor nuclei, in lumbar dorsal root ganglia, and in the trigeminal ganglion (Ninkina et al 2003). Lack of clear morphological and phenotypic differences were similarly observed in the CNS of α-synuclein null mutant mouse (Abeliovich et al 2000;Cabin et al 2002).…”

“…3). Prior work has shown no obvious phenotypic changes in the γ-synuclein null mouse (Ninkina et al 2003). As shown by Figure 5, we could not identify any morphologic changes in the organ of Corti in the knockout compared to the wild-type mouse; organ of Corti histology, outer and inner hair cell numbers, and spiral ganglion cell numbers were normal and identical in each zygosity (only wild-type and knockouts are shown in Figure 5).…”

“…γ-Synuclein null-mutant mice have been previously described (Ninkina et al 2003). α-Synuclein knockout mice were obtained from the Jackson Labs (http://jaxmice.jax.org, Stock#003692, Bar Harbor, ME, USA) and crossed multiple times onto C57BL/6 for strain maintenance.…”

Increased lipolysis and altered lipid homeostasis protect γ-synuclein–null mutant mice from diet-induced obesity

“…Production, genotyping, and initial characterization of γ-synucleinnull mutant mice on a C57Bl6J genetic background have been described previously (4). The colony was maintained by backcross breeding, and intercrosses were used for production of experimental cohorts (details provided in SI Methods).…”

“…To date, no clear cellular role is attributed to γ-synuclein, and ablation of γ-synuclein causes only minor changes in the nervous system (4)(5)(6)(7). Recently, we and others have reported high levels of γ-synuclein expression in adipose tissue of humans and other mammals (8,9).…”