The transcription factor Sox10 is a key regulator of peripheral glial development

Abstract

The molecular mechanisms that determine glial cell fate in the vertebrate nervous system have not been elucidated. Peripheral glial cells differentiate from pluripotent neural crest cells. We show here that the transcription factor Sox10 is a key regulator in differentiation of peripheral glial cells. In mice that carry a spontaneous or a targeted mutation of Sox10, neuronal cells form in dorsal root ganglia, but Schwann cells or satellite cells are not generated. At later developmental stages, this lack of peripheral glial cells results in a severe degeneration of sensory and motor neurons. Moreover, we show that Sox10 controls expression of ErbB3 in neural crest cells. ErbB3 encodes a Neuregulin receptor, and down-regulation of ErbB3 accounts for many changes in development of neural crest cells observed in Sox10 mutant mice. Sox10 also has functions not mediated by ErbB3, for instance in the melanocyte lineage. Phenotypes observed in heterozygous mice that carry a targeted Sox10 null allele reproduce those observed in heterozygous Sox10(Dom) mice. Haploinsufficiency of Sox10 can thus cause pigmentation and megacolon defects, which are also observed in Sox10(Dom)/+ mice and in patients with Waardenburg-Hirschsprung disease caused by heterozygous SOX10 mutations.

Figure 1

Targeted deletion of Sox10 and expression of the Sox10^lacZ allele in mice. (a) Schematic representation of the targeting strategy employed to disrupt the Sox10 gene. Shown are the targeting vector (top), the wild-type Sox10 locus (middle) and the mutated locus after homologous recombination (bottom). Noncoding and coding exons are represented by black or open boxes, respectively. Restriction sites for SpeI (P) and NcoI (N) as well as the location of the 5′ probe are indicated. (b) Southern blot analysis of DNA from adult heterozygous (+/−) and wild-type (+/+) mice after digestion with NcoI/SpeI. The expected size of the fragments detected by the probe used for hybridization are shown (a). (c) RT–PCR analysis of wild-type (+/+), heterozygous (+/−) and homozygous (−/−) embryos at E12.5 using primers specific for the coding region of Sox10. Results from 20, 23, and 26 cycles are shown for each genotype. Sox10^lacZ/+ (d–f) and Sox10^lacZ/Sox10^lacZ (g–i) embryos at E8.5 (d,g), E10.5 (e,h), and E12.5 (f,i) after X-gal staining.

Figure 2

Sox10 controls expression of ErbB3. Whole-mount in situ hybridizations of wild-type (a–d), Sox10^Dom/Sox10^Dom (e–l), and ErbB3–/− (m–p) embryos with probes specific for Sox10 (top), and ErbB3 (bottom). Shown are lateral (a,b,e,f,m,n) views of E10.5 embryos and the corresponding vibratome sections (c,d,g,h,o,p) on forelimb levels. Lateral (i,j) and dorsal (k,l) views of Sox10^Dom/Sox10^Dom embryos at E9.0. Arrows in f, j, and l point toward ErbB3-expressing cells close to the neural tube in Sox10^Dom/Sox10^Dom embryos; arrows in c, g, and o point toward the anlage of the primary sympathetic ganglion chain (sy); arrowheads in d, f, h, and j point toward the myotome that also expresses ErbB3. Bars (a,b,e,f,m,n) 1 mm; (c,d,g,h,o,p) 100 μm; (i–l) 300 μm.

Figure 3

Sox10 increases endogenous ErbB3 expression in N2A cells. (a,b) RT–PCR analysis of mRNA obtained from N2A cells that express Sox10, Sox11, or a mutant version of Sox10 (FL, wild-type cDNAs; Sox10fs, Sox10^Dom mutant; Kuhlbrodt et al. 1998b) in an inducible manner. Doxycycline (DOXA) was used to induce the expression of the transcription factors (+), which was compared to the uninduced state (−). ErbB3 transcript levels were compared in the various transfectants by semiquantitative PCR, using increasing numbers of amplification cycles (20, 23, and 26); in addition, the expression of GAPDH, Sox10, and Sox11 was monitored. (c) Northern blot analysis on 2 μg of poly(A)⁺ RNA from uninduced (left) and doxycycline-treated (right) N2A cells that express Sox10 in an inducible manner. The ErbB3-specific signal is indicated by an asterisk.

Figure 4

Sox10 controls peripheral glial cell development. (a–f) Immunohistological analysis of wild-type (a,b), Sox10^Dom/Sox10^Dom (c,d), and ErbB3^−/−(e,f) embryos at E11.5 on lumbar axial levels, using antibodies against B-FABP (red) and TuJ-1(green) to visualize peripheral glial cells and neuronal cells, respectively. B-FABP antibody signals (a,c,e) and an overlay of B-FABP and TuJ-1 antibody signals (b,d,f) are shown. The arrowhead in d points towards the abnormally shaped dorsal root entry zones in Sox10^Dom/Sox10^Dom mutants; the arrows point towards B-FABP-positive Schwann cell precursors that line spinal nerves in control and ErbB3^−/− mice. (g–l) In situ hybridization of wild-type (g,h), Sox10^Dom/Sox10^Dom (i,j), and ErbB3^−/− (k,l) embryos at E11.5 with probes specific for Sox10 (g,i,k) or Notch-1 (h,j,l). Sections on lumbar axial levels are shown. Bars (a–f) 100 μm; (g–l) 150 μm.

Figure 5

Appearance of dorsal root ganglia in homozygous Sox10 mutant animals. Histological and immunohistological analyses of dorsal root ganglia and spinal nerves in Sox10^lacZ/+ (a,b), wild-type (c–e), Sox10^lacZ/Sox10^lacZ (f,g), and Sox10^Dom/Sox10^Dom (h–j) animals at E11.5 (a,b,f,g) and E12.5 (c–e,h–j). (a,f) Immunohistological analysis using antibodies against B-FABP (red) and β-galactosidase (green). Note that B-FABP and β-galactosidase from the Sox10–lacZ reporter are coexpressed (yellow) in satellite glia of dorsal root ganglia of control mice. B-FABP is not expressed in Sox10^lacZ/Sox10^lacZ mice, although β-galactosidase-positive cells persist. (b,g). High-magnification of ventral roots stained with antibodies against peripherin (red) and β-galactosidase (green). Arrowheads point towards cells that express β-galactosidase; arrows point towards neuronal cells expressing peripherin. Note that the two proteins are coexpressed in neither control nor homozygous mutant mice, indicating that the β-galactosidase-positive precursor cells have not adopted a neuronal fate in Sox10^lacZ/Sox10^lacZmice. (c,h) Immunohistological analysis with antibodies against TuJ-1 (green) and B-FABP (red), which visualize neuronal and glial cells, respectively. Histological appearance of dorsal root ganglia (d,i) and intercostal nerves (e,j) at E12.5. Note the marked reduction in size of the ganglion in the mutant mice. In control mice, nuclei associated with the intercostal nerve are abundant (arrows in e), which are not observed in the Sox10 mutant. Note also the abnormal dorsal root entry zones in homozygous mutants, which are indicated by arrowheads in f, h, and i. Bars (a,f) 80 μm; (b,g) 15 μm; (c,d,h,i) 150 μm; (e,j) 50 μm.

Figure 6

Loss of motoneurons in Sox10^Dom/Sox10^Dom and ErbB3^−/− mutant mice. Sections of the cervical spinal cord of wild-type (a) and Sox10^Dom/Sox10^Dom (b) mutant animals at E18.5 after in situ hybridization with a VAChT specific probe. (c,d) Motoneuron numbers in cervical, thoracic, and lumbar segments of spinal cords obtained from wild-type (blue columns), Sox10^Dom/Sox10^Dom (red columns), and ErbB3^−/− (green columns) mutants at E15.5 (c) and E18.5 (d). Mean numbers of motoneurons per section +/− S.D. are shown (n = 4 embryos for each genotype and developmental stage). Counts were not corrected for neuron size, and the numbers of neurons at different developmental stages are therefore not strictly comparable. Bar (a,b) 100 μm.

Figure 7

Sox10 controls development of melanoblasts and expression of the trp-2 gene. (a–f) Transverse sections of wild-type (a,b), heterozygous (c,d), and homozygous (e,f) Sox10^lacZ mice at E12.5 on corresponding hindlimb levels. Embryos were hybridized with probes specific for c-kit (a,c,e; main panels), mi (a,c,e; insets), and trp-2 (b,d,f). (g) Melanoblasts positive for c-kit, mi, or trp-2 in wild-type (+/+, black), heterozygous (+/−, gray), and homozygous (−/−, white) Sox10-deficient mice at E12.5. The numbers of positive cells in wild-type mice identified by each marker were arbitrarily set to 100%. (h) Luciferase reporter assay determining the interaction of Sox10 and the trp-2 gene. Reporter genes were transfected into tet-on N2A cells. Luciferase was expressed under the control of the 3.7-kb trp-2 promoter (trp2luc), the P₀ promoter (P0luc), or the thymidine kinase promoter (TKluc) or were lacking a specific promoter (pGL2). Luciferase activity was measured before and after doxycycline treatment. Sox10-dependent promoter activation was expressed as the ratio between these two values. Bars represent the result from three independent transfections +/− S.E.M.