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Fig. 1. Schematic diagram of Noelin isoform exon composition. (A) Noelins are made by differential promoter usage and alternative splicing. Exon structure was first elucidated in the rat by Danielson et al. (1994). The olfactomedin domain is indicated, as well as the location of the two cysteine residues conserved in all Noelins and homologous to cysteines in Olfactomedin that are responsible for disulfide bonding in multimerization (asterisks in M region). (B) Noelin exon terminology used in this work is shown, with predicted signal peptide cleavage sites indicated with arrowheads.
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Fig. 2. Noelin-4 is a secreted, glycosylated protein. (A) Noelin constructs used in these studies are shown schematically. Noelin-4 was myc-tagged at the carboxy terminal. Noelin-4DA-myc is Noelin-4-myc with the A exon removed. (B) Noelin-4-myc was immunoprecipitated from oocyte (o, lane 1) and supernatant (s, lane 2) fractions. In vitro-translated protein (IVT) is shown in lane 3. Oocyte and supernatant fractions contain Noelin-4 protein that is larger than the size of in vitro- translated core protein. (BV) Anti-myc Western blot of embryos injected with Noelin-4-myc or Noelin-4 (for a Western blot control) as indicated. Proteins were run on SDS-PAGE either as embryo lysate (lane 1), lysate treated with PNGase F (deglyc, lane 2) or in vitro-translated protein (IVT, lane 3). Proteins in the deglycosylated sample collapsed to the size of in vitro-translated protein. (C) Noelin-4DA-myc immunoprecipitated from the oocyte fraction only, and was not found in the supernatant fraction (lane 2 versus lane 3). Control oocytes and supernatant are shown in lanes 4-6.
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Fig. 3. Developmental expression patterns of Noelins. (A) Noelin temporal expression patterns. Embryos were harvested at the stages indicated and examined for the presence of the specific Noelin isoforms by RT-PCR. EF1a is a loading control, -RT is a control for genomic DNA contamination. Primer pairs used hybridize to only one splice variant each, as indicated. Noelin expression is observed weakly from neural plate stages, with strong expression from late neurula stages. (B-F) Spatial expression pattern of Noelin-3/4 (Y exon in situ hybridization, purple staining). Anterior is to the left. (B) Side view of stage 27 embryo with staining in cranial ganglia (arrowhead) and spinal cord; (C) stage 29 embryo with staining in trigeminal ganglion (arrowhead) and spinal cord; (D) anterior view of stage 26 embryo highlighting olfactory placode expression (arrowhead); (E) dorsal view of stage 42 embryo with staining in cranial ganglia, eye, and neuromasts; (F) magnification of boxed region in panel D showing neuromast expression (arrowhead).
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Fig. 4. Noelin-3 and -4 are induced by neurogenin. (A, B) Embryos were injected in one cell at the two-cell stage with 100 pg of X-ngnr-1 and cultured to stage 24. Whole mount in situ hybridization for N-tubulin (A) or the Y exon of Noelin-3 and -4 (B) is shown. Ectopic neurons staining with the markers are indicated with arrowheads. (C-E) cross-sections of animal caps from embryos injected with 100 pg X-ngnr-1 or lacZ in 2/2 cells, excised at stage 9 and cultured to stage 22. Arrows point to regions staining with the markers. (C) N-tubulin staining; (D) Y exon staining; (E) lacZ-injected, N-tubulin staining. Embryos for this experiment were derived from pigmented mothers; brown color is due to pigment granules. (F) RT-PCR on stage 22 animal caps explanted at stage 10, derived from embryos injected with lacZ (c, lane 2), X-ngnr-1 (ng, lane 3), or XNeuroD (nd, lane 4), or on whole embryo controls (e, lane 1). Both XNeuroD and X-ngnr-1 induced expression of all four Noelin isoforms. RNA without reverse transcriptase was used as a negative control (-, lane 5). Primers used are indicated; each Noelin set hybridizes to only the indicated isoform. SybII = synaptobrevinII, a marker for differentiating neurons (Knecht et al., 1995).
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Fig. 5. Noelin-4 over-expression results in expansion of neural fate. Embryos injected with Noelin-4 exhibit enlarged and ectopic neural tissue. Embryos were injected with 500 pg (A - G, P - S) or 1 ng (H - O) of Noelin-4 mRNA, 500 pg Noelin-3 (T, U), and 100 pg of lac Z mRNA as a lineage tracer. h-galactosidase activity was assessed with X-gal (turquoise, A-G) or Magenta-Gal (magenta, H-O) and embryos were stained for Sox-2 expression. (A-C) Neural plate stage embryos injected with (A) Noelin-4 (AMY), (B) Noelin-2 (AMZ) or (C) lacZ. Injected side is to the left, embryos are photographed from the dorsal side, oriented with anterior pointing up. Anterior neural plate is indicated with an arrowhead. Note expansion of the neural plate in panel A. (D - G) Embryos were harvested at stage 29 and stained for Sox-2 expression. (D) Control side, (E) injected side of same embryo. Neural retina is revealed by Sox-2 staining, note that injected side eye is larger than control side (arrowheads). (F) Cross section through midbrain region; (G) comparison of neural retinas from both sides of the embryo magnified to the same degree. (H - O) Examples of embryos harvested at stage 35 and stained for Sox-2 expression. (H, L) Control side; (I, M) injected side. Panels J, N, and O are cross- sections through the head regions with the section level indicated on panels I and M. Panel K is a magnification of the injected side in panel J. Note expansion of neural tissue and ectopic Sox-2 staining (arrowhead). Panel O shows an ectopic cement gland ventral to the eye (arrow) that is discontinuous with the endogenous cement gland (see arrowhead in panel M). (P-S) N-tubulin staining of embryos injected with Noelin-4 (P, R) or Noelin-1 (Q, S). (P, Q) Neural plate stage embryos, with injected side to the left, anterior pointing to top. (R, S) Embryos at stage 24 with anterior to the left. Arrowheads indicate bulging tissue on the injected side in panels P, R. (T, U) Noelin-3 causes similar neural territory expansion. Noelin-3 (BMY) injection, Sox-2 staining. Bars and brackets outline width of neural structures in two different embryos on the injected side (bottom half) and uninjected control side (top half).
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Fig. 6. Ectoderm in Noelin-4 embryos is diverted toward a neural fate. (A-C) Mesoderm is not induced by Noelin-4. (A) RT-PCR of animal caps injected with the indicated isoform (N1 = Noelin-1, 500 pg; N4 = Noelin-4, 500 pg; N1 + N4 = 500 pg each; nog = 100 pg noggin; e = stage 22 embryo control; c = 500 pg lacZ-injected animal cap control). NCAM indicates neural induction, MA (muscle actin) indicates mesoderm. EF1a is a loading control. (B, C) Mesodermal MA expression is not affected by Noelin-1 over-expression. Neural plate stage embryos injected and stained for MA: (B) stage 15 embryo injected with Noelin-4 (1 ng); (C) Noelin-1 injected stage 16 (1 ng). Arrowheads indicate injected side. (D-G) Anti-phospho Histone H3 staining of embryos injected with Noelin-4 (500 pg) and lacZ (50 pg). No difference in proliferation was observed. (D) Neural plate stage embryo, anterior to the left, injected side down. Brown dots indicate anti-phospho Histone H3 positive cells. (E - G) Stage 24 embryo. (E) Anterior to the left, injected side down. (F) Closeup of dorsal view (boxed area in panel E, midline marked by dashed line); (G) cross section (level of section indicated in panel E) with midline of embryo marked by vertical line. Note the expansion of tissue on injected side in panel F (below dotted line), which contains no extra proliferative figures. (H, I) Cell death assay of Noelin-injected embryos. TUNEL staining of embryos injected in 2 of 2 cells with 500 pg Noelin- 4 (H, stage 17) or lacZ (I, stage 18). Anterior is oriented up. No change is noted in TUNEL staining between these embryos (n = 8 each). (J, K) Conversion of epidermal territory. Embryos injected with 1 ng Noelin-4 (J, stage 16) or Noelin-1 (K, stage 15) and stained for epidermal keratin. Neural plate territory and midline are indicated with dashed line; injected side is to the left (arrowheads). In panel J, note that the neural plate remains larger on the injected side. (L - Q) Neural crest formation is perturbed by Noelin-4 over-expression. Embryos were injected with 1 ng Noelin-4 and stained for the neural crest marker XSlug (L, M) or XTwist (N - Q). (L) Stage 15 embryo, Noelin-4-injected side is to the left (arrowhead). Note the loss of XSlug staining on the injected side. (M) Stage 16 embryo injected with Noelin-1 (BMZ). (N) Control side; (O) injected side; note missing streams of neural crest staining (bracket) and overgrown tissue near neural tube (arrowhead). (Q) Dorsal view, with overgrown tissue outlined (arrowhead). (P) Cross section of a similar embryo shows mandibular neural crest staining is missing from injected side (arrows). Extra tissue formed by Noelin-4 ectopic expression (dashed outline) is negative for XTwist expression. m, mandibular crest; h, hyoid crest, ba and bp: anterior and posterior branchial crest; e, eye; cg, cement gland; mb, midbrain.
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Fig. 7. Noelin-4 binds to Noelin-1. (A) Noelin-4-myc and Noelin-1-flag constructs used are shown diagrammatically. Noelin-1 bears an internal Flag epitope when designated with a plus sign (+), or is without a tag when designated with a minus sign (ï°). O, oocyte; IVT, in vitro-translated protein; m, myc; f, flag. (B) Co- immunoprecipitation assay in Xenopus oocytes. Oocytes were injected as indicated and cultured in the presence of 35S-methionine. Oocyte controls were injected with an untagged version of Noelin-1 and immunoprecipitated with either myc or flag (lanes 1, 2). In vitro-translated proteins (lanes 3, 4) are compared to oocyte- translated proteins (lanes 5, 6). Samples were immunoprecipitated with the indicated antibody (m = myc; f = flag). Noelin-4-myc is indicated with arrowheads; Noelin-1-flag is indicated with arrows. (C) IP-Western blot. COS-7 cells were transfected with the indicated plasmids and then immunoprecipitated with either myc or flag antibodies. Lysate (L) and supernatant (S) fractions were then resolved on SDS-PAGE and transferred to nitrocellulose before enhanced chemiluminescence detection with the indicated antibody. Some of the precipitating antibodies were also eluted during sample preparation; heavy and light-chain immunoglobulin bands detected with the Western secondary antibody are indicated with asterisks in control lane 1. Noelin-4-myc is denoted with an arrowhead; Noelin-1-flag is denoted with arrows. Myc pull-down of Noelin-4-myc samples brought down a band that immunoreacted with myc on the Western blot (arrowhead, lanes 5, 6), as did flag pull-down on samples transfected with Noelin-1-flag and subsequently blotted for flag (lanes 7, 8). Samples transfected with both plasmids and immunoprecipitated with anti-myc contained flag-immunoreactive bands at the size of Noelin-1-flag (arrows, lanes 9, 10).
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