XB-ART-38371BMC Dev Biol July 28, 2008; 8 87.
Expression study of cadherin7 and cadherin20 in the embryonic and adult rat central nervous system.
Vertebrate classic cadherins are divided into type I and type II subtypes, which are individually expressed in brain subdivisions (e.g., prosomeres, rhombomeres, and progenitor domains) and in specific neuronal circuits in region-specific manners. We reported previously the expression of cadherin19 (cad19) in Schwann cell precursors. Cad19 is a type II classic cadherin closely clustered on a chromosome with cad7 and cad20. The expression patterns of cad7 and cad20 have been reported previously in chick embryo but not in the developing and adult central nervous system of mammals. In this study, we identified rat cad7 and cad20 and analyzed their expression patterns in embryonic and adult rat brains. Rat cad7 protein showed 92% similarity to chick cad7, while rat cad20 protein had 76% similarity to Xenopus F-cadherin. Rat cad7 mRNA was initially expressed in the anterior neural plate including presumptive forebrain and midbrain regions, and then accumulated in cells of the dorsal neural tube and in rhombomere boundary cells of the hindbrain. Expression of rat cad20 mRNA was specifically localized in the anterior neural region and rhombomere 2 in the early neural plate, and later in longitudinally defined ventral cells of the hindbrain. The expression boundaries of cad7 and cad20 corresponded to those of region-specific transcription factors such as Six3, Irx3 and Otx2 in the neural plate, and Dbx2 and Gsh1 in the hindbrain. At later stages, the expression of cad7 and cad20 disappeared from neuroepithelial cells in the hindbrain, and was almost restricted to postmitotic cells, e.g. somatic motor neurons and precerebellar neurons. These results emphasized the diversity of cad7 and cad20 expression patterns in different vertebrate species, i.e. birds and rodents. Taken together, our findings suggest that the expression of cad7 and cad20 demarcates the compartments, boundaries, progenitor domains, specific nuclei and specific neural circuits during mammalian brain development.
PubMed ID: 18801203
PMC ID: PMC2564927
Article link: BMC Dev Biol
Species referenced: Xenopus
Genes referenced: arhgef5 cdh20 dbx2 egr2 gata2 gbx2.1 gbx2.2 gsx1 igl irx3 isl1 lbx1 npat otx2 pax6 pes1 six3 sox10 tcf3 vsig1
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|Figure 1. Amino acid sequences and chromosome mapping of rat cad7 and cad20. A: Alignments of rat cad7 and cad20 protein sequences. Asterisks indicate identical amino acids between cad7 and cad20 proteins. Numbers indicate percentage of identical amino acids in each domain and catenin binding domains. B: The positions of cad7, cad19 and cad20 on the human, rat, mouse and chick genomes, based on genome data search. Directions of arrows indicate coding on forward (right) and reverse (left) strands, respectively. C: Phylogenetic tree for type II classic cadherins. m, mouse; r, rat; h, human; c, chick; X, Xenopus.|
|Figure 2. Expression patterns of cad7 in the developing rat embryo. A-C: The expression of cad7 mRNA in the anterior margin of the early neural plate at E9.5–9.75 (arrowhead in A, B and C), and in the lateral plate at E9.75 (arrow in C). These pictures show lateral (A), ventral (B) and dorsal (C) views. D: Lateral view showing the expression of cad7 in the brain region anterior to the midbrain/hindbrain boundary (arrowhead) and caudal neural tube (arrow) at E10.5. D': Dorsal view of D. The expression of cad7 is detected at the edge of the neural plate and part of migrating neural crest cells (arrowheads). E-G: Expression of cad7 in the forebrain and midbrain (E). Cad7 is expressed in the dorsal region of the otic vesicle (ov), and in the olfactory epithelium (oe) and retina (r) at E11.5 (E). G is a cross-section at the fore limb (fl) level. In the hindbrain and spinal cord, cad7 is expressed in the dorsal neuroepithelium and the expression is absent in the roof plate (rp) (F, G). E and F images indicate lateral and ventral view, respectively. H: Lateral view of cad7 expression in the pharyngeal region at E12.0. Arrow and arrowhead indicate expression of cad7 in the pharyngeal groove (pg) and otic vesicle (ov), respectively. I-J: Lateral view of cad7 staining in the brain of E12.5 embryos. Arrow in I indicates the expression of cad7 in the ventral domains of prosomere3 (p3) and secondary prosencephalon. No expression of cad7 in the dorsal root ganglion cells at the trunk level (J). K-N: On cross-sections from E14.5 embryo, cad7 transcripts are detected in the subpopulation of motor neurons (mn) but not in the dorsal root ganglion or Schwann cell precursors (arrowheads in K, and M) expressing Sox10, along motor nerve (arrowheads in L and N). al, pharyngeal arch 1; da, dorsal aorta; ctx, cerebral cortex; mb, midbrain. Scale bars: 200 μm in A-C, G and K-N; 400 μm in D; 100 μm in D'; 500 μm in E and H; 300 μm in F; 1 mm in I and J.|
|Figure 3. Expression of cad7 and cad20 and transcription factors in the early neural plate. Images shown in A, D, E, O and B, C, F-N are taken from the anterior and dorsal sides, respectively. A-I: Cad7 mRNA is expressed in the forebrain region (A). The anterior border of cad7 expression in the hindbrain is consistent with that of Krox20 in the r3 (green arrowhead in B and C). At E10.5, cad20 is expressed in the forebrain region and the expression region overlaps with that of Six3 (D, E). Cad20 expression is absent in the anterior margin of the neural plate (arrow in E), which is different from Six3 expression (arrow in D). Blue arrowheads in D and G indicate the expression boundary between Six3 and Irx3. The boundary between cad20- and Irx3-domains demarcates the position of the presumptive zona limitans intrathalamica (ZLI) (arrowhead in F, G and H). I-O: At E10.5, the posterior border of cad7 expression corresponds to the midbrain/hindbrain boundary (MHB) as indicated by Gbx2 (black arrowhead in M). The border of cad20 expression is not consistent with the posterior border of Otx2 (black arrowhead in N), the expression is detected in the r2 region expressing Gbx2. The posterior border of cad20 is detected anterior to forebrain/midbrain boundary (arrows in O). P: Schematic illustrations of mapping of cad7 and cad20 in the early stages. pos, pre otic sulcus; fb, forebrain; mb, midbrain; hb, hindbrain, anr, anterior neural ridge; MHB, midbrain/hindbrain boundary. Scale bars: 200 μm in A-H; 400 μm in I-L; 200 μm in M-O.|
|Figure 4. Mapping of cad7 and cad20 expression on progenitor domains in the hindbrain. A-D: Expression analysis on the dissected whole brain (A, C) and cross-sections at r7 (B) and r6 level (D) of E11.5 embryo. Images of A and C are taken from the lateral side of the brain. At E11.5, cad7 mRNA is mainly detected in the dorsal domain of the neural tube posterior to r5/6 boundary (arrow in A), and the ventral border of cad7 corresponds to the dorsal border of Dbx2 (arrowhead in B, cross-section at r7 level after double detection). At E11.5, cad20 transcripts are highly detected in the middle domain of the hindbrain anterior to r6/7 boundary (arrow in C), and the dorsal area of cad20-domain overlaps with the ventral area of Gsh1-domain (arrowhead in D, cross-section at r6 level after double detection). E-J: Expression analysis on the dissected whole brain (E, I) and serial cross-sections at r7 level (F-H, and J) from E12.5 embryo. Images of E and I are taken from the lateral side of the brain. The ventral border of cad7 in the dorsal progenitor domain is consistent with the dorsal border of Dbx2 (arrowheads in F and G), and part of cad7-expressing progenitors gives rise to Lbx1-positive dorsal interneurons (Dl4-6) (H). The expression of cad20 in the middle domain of the hindbrain gradually disappears at E12.5 (I), and another expression domain of cad20 also appears in a more ventral region (arrow in I and J). K-L: BrdU detection after in situ hybridization. The domain of cad20-expressing cells corresponds to that of cells expressing Gata2, a V2 interneuron lineage maker (brackets in K and L), and cad20 expressing cells are progenitor cells incorporating BrdU (arrow in L). M-N: Summary of expression of cad7 and cad20 along D-V axis at E11.5 (M) and E12.5 (N). Left: expression domains at r5 and r7. Right: progenitor domains defined with expressions of homeodomain transcription factors and cadherins. Broken lines indicate the border between basal and alar plates. V0–V2, V0–V2 interneuron; SM, somatic motor neuron, BM, branchial motor neuron. Scale bars: 500 μm in A, C, E and I; 150 μm in B, D; 200 μm in F, G, H and J; 200 μm in K, L.|
|Figure 5. Expression of cad7 and cad20 in the rhombomeres and boundaries. A-D: Expression of cad7 and cad20 in E11.5 (A, B) and E12.5 (C, D) hindbrains which are prepared in open-book style. Cad7 transcripts are localized in the boundaries (arrow and arrowhead in A, C). Cad20 is strongly expressed in the middle area in the r1-6 and r4 (asterisk in B). E: Horizontal section of whole-mount staining embryos with cad7 probe. Cad7 mRNA is highly expressed in the rhombomere boundary cells (arrowheads in E). Scale bars: 500 μm in A-D; 200 μm in E.|
|Figure 6. Expression of cad7 in the motor neurons and precerebellar systems. A-E: Expression of cad7 and cad20 on serial cross-sections from the hindbrain of E14.5 rat embryo at r7 level. (B) High magnification of the image shown in A. Expression of cad7 and cad20 is detected in hypoglossal motor nuclei (nXII) expressing Islet1/2 (A, B, C and E). No expression of cad7 is seen in the ventricular zone (VZ) of the dorsal area (D). F-O: Expression of Pax6, cad7 and cad20 on serial cross-sections at E18.5. Pax6 protein is detected in both the lower rhombic lip (LRL) (F), posterior extramural migrating stream (pes) (J and arrows in L) and the external cuneate nucleus (ECN) (bracket in J). Cad7 is expressed in nXII (bracket in G), vagus motor nuclei (nX) (arrowhead in G), lateral reticular nuclei (LRT) (arrow in G), the ECN (bracket in K), the nucleus of the solitary tract (Sol), and in the intermediate reticular zone (IRt). Cad7-expressing cells are migrating on the surface of the brain, which is similar to Pax6-expressing cells (arrows in L, M and arrowheads in N and O). Cad7 is also expressed in the medial accessory olive (MAO) nuclei expressing cad6 (G and I). Cad20 is expressed in nXII but not in nX (bracket in H). P-S: Serial cross-sections of E18.5 Pax6 homozygous mutant rat (rSey2/rSey2). Pax6 protein is undetectable (P), while expression of cad7 is detected in LRT (arrow in Q) and MAO expressing cad6 (S). nXII motor nuclei and ECN are missing in the Pax6 homozygous mutant (bracket and arrowhead in Q, respectively). The expression of cad20 is also undetectable, which is similar to the cad6 expression (bracket in R and S). T: Summary of expression of cad7 and cad20. Scale bars: 300 μm in A and E and F-I; 100 μm in B and C; 200 μm in D, J-M and P-S; 50 μm in N and O.|
|Figure 7. Expression of cad7 in the brainstem and cerebellum in the foetus. A-J: Comparison of expression patterns of Pax6 and cad7 in the brainstem and cerebellum of the wild type (A, B, E and F) and Pax6 homozygous mutant rat (rSey2/rSey2) (C, D, G and H) on serial sagittal sections. At E20.5, Pax6 and cad7 are expressed in the pontine nucleus (PN), reticular nucleus (RT) (arrowheads in A and B) and the external germinal layer (EGL) (arrows in E and F). In the Pax6 mutant, cad7 expression is detected in the remaining RT (arrowhead in D), which is similar to Pax6 expression (arrowhead in C). The expression of Pax6 and cad7 is observed in EGL of the Pax6 mutant (arrows in G, H). I-L: Cross-sections of the E20.5 rat cerebellum. Cad7 is also expressed in the cerebellar neuroepithelium (cne) (arrows in J, bracket in L) and cerebellar deep nuclei (arrowheads in J) in contrast to the expression of Pax6 (I and K). M-N: Higher magnifications of E and F. The expression of Pax6 and cad7 is detected in both EGL (bracket) and migrating cells. URL, upper rhombic lip. Scale bars: 500 μm in A-D; 100 μm in E-H; 300 μm in I and J; 200 μm in K-M.|
|Figure 8. Expression of cad7 in the brainstem and cerebellum in the adult. A-H: Expression of cad7 and cad20 in motor neurons and cerebellum on cross-sections of 8-week-old (P60) rat. The expression of cad7 is detected in both nX and nXII (A) but the expression of cad20 is only detected in nXII (B). C and D are high magnification images of cad7 and cad20 expression in nXII, which are indicated in A and B, respectively. In the cerebellum, cad7 and cad20 are expressed in the internal granular layer (IGL) (E, F), and scattered large cells expressing cad7 are detected in IGL (arrowheads in G, high magnification of E). Intense signal of cad20 is observed at the interface between molecular layer (ML) and IGL (arrowheads in H, high magnification of F). I-P: Expression of cad7 in the pons and medulla oblongata on cross-sections of the P60 rat. Expression of cad7 is detected in the pontine nucleus (PN) (I) and reticular nucleus (RT) (J). K and L are high magnification images of cad7 expression in the PN and RT indicated in I and J, respectively. Cad7 is expressed in the lateral reticular nuclei (LRT) and external cuneate nuclei (ECN) but not in the inferior olive nucleus (IO). O and P are high magnification of cad7-expressing cells in the LRT and ECN shown in M and N. Q-R: Summary of expression of cad7 and cad20 (Q) and schematic illustration showing the expression of cad7 and neuronal circuits in the hindbrain (R). Lines in R indicate connection between precerebellar neurons and layers of the cerebellum. PCL, Purkinje cell layer; WM, white matter. Scale bars: 500 μm in A, B, E, F, I, J; 400 μm in C, D, K, L, P; 200 μm in G, H, O; 500 μm in E, F, M, N.|
References [+] :
Altman, Development of the precerebellar nuclei in the rat: III. The posterior precerebellar extramural migratory stream and the lateral reticular and external cuneate nuclei. 1988, Pubmed