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Retinoic acid is a potential dorsalising signal in the late embryonic chick hindbrain.

Wilson LJ, Myat A, Sharma A, Maden M, Wingate RJ - BMC Dev. Biol. (2007)

Bottom Line: Intriguingly, transcripts of cellular retinoic acid binding protein 1 are always found at the interface between dividing and post-mitotic cells.At the rhombic lip, retinoic acid is likely to act as a dorsalising factor in parallel with other roofplate signalling pathways.While its precise role is unclear, retinoic acid is potentially well placed to regulate temporally determined cell fate decisions within the rhombic lip precursor pool.

View Article: PubMed Central - HTML - PubMed

Affiliation: MRC Centre for Developmental Neurobiology, King's College London, 4th floor New Hunt's House, Guy's Campus, London SE1 1UL, UK. leigh.wilson@kcl.ac.uk

ABSTRACT

Background: Human retinoic acid teratogenesis results in malformations of dorsally derived hindbrain structures such as the cerebellum, noradrenergic hindbrain neurons and the precerebellar system. These structures originate from the rhombic lip and adjacent dorsal precursor pools that border the fourth ventricle roofplate. While retinoic acid synthesis is known to occur in the meninges that blanket the hindbrain, the particular sensitivity of only dorsal structures to disruptions in retinoid signalling is puzzling. We therefore looked for evidence within the neural tube for more spatiotemporally specific signalling pathways using an in situ hybridisation screen of known retinoic acid pathway transcripts.

Results: We find that there are highly restricted domains of retinoic acid synthesis and breakdown within specific hindbrain nuclei as well as the ventricular layer and roofplate. Intriguingly, transcripts of cellular retinoic acid binding protein 1 are always found at the interface between dividing and post-mitotic cells. By contrast to earlier stages of development, domains of synthesis and breakdown in post-mitotic neurons are co-localised. At the rhombic lip, expression of the mRNA for retinoic acid synthesising and catabolising enzymes is spatially highly organised with respect to the Cath1-positive precursors of migratory precerebellar neurons.

Conclusion: The late developing hindbrain shows patterns of retinoic acid synthesis and use that are distinct from the well characterised phase of rostrocaudal patterning. Selected post-mitotic populations, such as the locus coeruleus, appear to both make and break down retinoic acid suggesting that a requirement for an autocrine, or at least a highly localised paracrine signalling network, might explain its acute sensitivity to retinoic acid disruption. At the rhombic lip, retinoic acid is likely to act as a dorsalising factor in parallel with other roofplate signalling pathways. While its precise role is unclear, retinoic acid is potentially well placed to regulate temporally determined cell fate decisions within the rhombic lip precursor pool.

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Expression of Raldh1. In situ hybridisation was performed on wholemount embryos with DIG- or fluorescein-labelled riboprobes. Unless otherwise stated, rostral is top, in views of the dorsal embryo, and to the right in lateral views. Abbreviations: midbrain (mb), hindbrain (hb), cerebellum (cb), rhombomere 1 (r1). A. At e3.5, in a lateral view of a wholemount embryo, Raldh1 is located in the eye and presumptive locus coeruleus (LC) of ventral r1 (arrow). B. Dorsal view at e5. C. Transverse section (through level indicated by dashed line in B) identifies expression in the LC. D. Expression at e6 of Raldh1 in a transverse section through rostral rhombomere 1. E. Expression of tyrosine hydroxylase (TH) at e6 in a matched transverse section of rostral r1. F. Transverse section through r1 at e6 showing double in situ hybridisation for Raldh1 (blue) and Cath1 (red). G. Dorsal view of hindbrain at e6.5 showing bilateral expression within putative isthmo-optic territory (arrows). H. Transverse section through the mid/hindbrain (dashed line in G). I. Expression relative to the cerebellum (midbrain removed) in a lateral view at e7 (arrow). J. Expression in vestibuloacoustic territory at e7 (arrows).
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Figure 1: Expression of Raldh1. In situ hybridisation was performed on wholemount embryos with DIG- or fluorescein-labelled riboprobes. Unless otherwise stated, rostral is top, in views of the dorsal embryo, and to the right in lateral views. Abbreviations: midbrain (mb), hindbrain (hb), cerebellum (cb), rhombomere 1 (r1). A. At e3.5, in a lateral view of a wholemount embryo, Raldh1 is located in the eye and presumptive locus coeruleus (LC) of ventral r1 (arrow). B. Dorsal view at e5. C. Transverse section (through level indicated by dashed line in B) identifies expression in the LC. D. Expression at e6 of Raldh1 in a transverse section through rostral rhombomere 1. E. Expression of tyrosine hydroxylase (TH) at e6 in a matched transverse section of rostral r1. F. Transverse section through r1 at e6 showing double in situ hybridisation for Raldh1 (blue) and Cath1 (red). G. Dorsal view of hindbrain at e6.5 showing bilateral expression within putative isthmo-optic territory (arrows). H. Transverse section through the mid/hindbrain (dashed line in G). I. Expression relative to the cerebellum (midbrain removed) in a lateral view at e7 (arrow). J. Expression in vestibuloacoustic territory at e7 (arrows).

Mentions: The production of retinoic acid in the embryo relies chiefly on the action of three retinaldehyde dehydrogenase enzymes (Raldh1, 2 and 3), which perform the second step of the conversion of retinol into the biologically active all-trans- and cis-retinoic acid. At e3.5, Raldh1 is restricted to the dorsal retina and a cluster of cells within rhombomere 1 (Fig. 1A). Transverse sections of rhombomere 1 at e5 (Fig. 1B, C) suggest these cells lie within the noradrenergic, locus coeruleus. To confirm their identity, we examined the expression of mRNA for tyrosine hydroxylase (TH), which converts tyrosine to L-dopa in the synthesis of noradrenalin. In situ hybridisations were performed on stage-matched embryos with Raldh1 (Fig. 1D) and TH (Fig. 1E) and show that transcripts are co-localised. Double in situ hybridisation reveals that Raldh1-positive neurons (blue) lie well outside the developing external granule cell layer (EGL) identified by Cath1 (red) expression (Fig. 1F). From ~e6.5, Raldh1 expression is found additionally within a discrete bilateral nucleus, rostral to the cerebellum, at the interface between hindbrain and midbrain (Fig. 1G). In transverse section (Fig. 1H) and following more extensive dissection (Fig. 1I), these neurons lie close to the isthmo-optic nucleus [31-33]. At e7, superficial bilateral patches of Raldh1 expression can be seen in the vestibuloacoustic region of the hindbrain (Fig. 1J).


Retinoic acid is a potential dorsalising signal in the late embryonic chick hindbrain.

Wilson LJ, Myat A, Sharma A, Maden M, Wingate RJ - BMC Dev. Biol. (2007)

Expression of Raldh1. In situ hybridisation was performed on wholemount embryos with DIG- or fluorescein-labelled riboprobes. Unless otherwise stated, rostral is top, in views of the dorsal embryo, and to the right in lateral views. Abbreviations: midbrain (mb), hindbrain (hb), cerebellum (cb), rhombomere 1 (r1). A. At e3.5, in a lateral view of a wholemount embryo, Raldh1 is located in the eye and presumptive locus coeruleus (LC) of ventral r1 (arrow). B. Dorsal view at e5. C. Transverse section (through level indicated by dashed line in B) identifies expression in the LC. D. Expression at e6 of Raldh1 in a transverse section through rostral rhombomere 1. E. Expression of tyrosine hydroxylase (TH) at e6 in a matched transverse section of rostral r1. F. Transverse section through r1 at e6 showing double in situ hybridisation for Raldh1 (blue) and Cath1 (red). G. Dorsal view of hindbrain at e6.5 showing bilateral expression within putative isthmo-optic territory (arrows). H. Transverse section through the mid/hindbrain (dashed line in G). I. Expression relative to the cerebellum (midbrain removed) in a lateral view at e7 (arrow). J. Expression in vestibuloacoustic territory at e7 (arrows).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC2266733&req=5

Figure 1: Expression of Raldh1. In situ hybridisation was performed on wholemount embryos with DIG- or fluorescein-labelled riboprobes. Unless otherwise stated, rostral is top, in views of the dorsal embryo, and to the right in lateral views. Abbreviations: midbrain (mb), hindbrain (hb), cerebellum (cb), rhombomere 1 (r1). A. At e3.5, in a lateral view of a wholemount embryo, Raldh1 is located in the eye and presumptive locus coeruleus (LC) of ventral r1 (arrow). B. Dorsal view at e5. C. Transverse section (through level indicated by dashed line in B) identifies expression in the LC. D. Expression at e6 of Raldh1 in a transverse section through rostral rhombomere 1. E. Expression of tyrosine hydroxylase (TH) at e6 in a matched transverse section of rostral r1. F. Transverse section through r1 at e6 showing double in situ hybridisation for Raldh1 (blue) and Cath1 (red). G. Dorsal view of hindbrain at e6.5 showing bilateral expression within putative isthmo-optic territory (arrows). H. Transverse section through the mid/hindbrain (dashed line in G). I. Expression relative to the cerebellum (midbrain removed) in a lateral view at e7 (arrow). J. Expression in vestibuloacoustic territory at e7 (arrows).
Mentions: The production of retinoic acid in the embryo relies chiefly on the action of three retinaldehyde dehydrogenase enzymes (Raldh1, 2 and 3), which perform the second step of the conversion of retinol into the biologically active all-trans- and cis-retinoic acid. At e3.5, Raldh1 is restricted to the dorsal retina and a cluster of cells within rhombomere 1 (Fig. 1A). Transverse sections of rhombomere 1 at e5 (Fig. 1B, C) suggest these cells lie within the noradrenergic, locus coeruleus. To confirm their identity, we examined the expression of mRNA for tyrosine hydroxylase (TH), which converts tyrosine to L-dopa in the synthesis of noradrenalin. In situ hybridisations were performed on stage-matched embryos with Raldh1 (Fig. 1D) and TH (Fig. 1E) and show that transcripts are co-localised. Double in situ hybridisation reveals that Raldh1-positive neurons (blue) lie well outside the developing external granule cell layer (EGL) identified by Cath1 (red) expression (Fig. 1F). From ~e6.5, Raldh1 expression is found additionally within a discrete bilateral nucleus, rostral to the cerebellum, at the interface between hindbrain and midbrain (Fig. 1G). In transverse section (Fig. 1H) and following more extensive dissection (Fig. 1I), these neurons lie close to the isthmo-optic nucleus [31-33]. At e7, superficial bilateral patches of Raldh1 expression can be seen in the vestibuloacoustic region of the hindbrain (Fig. 1J).

Bottom Line: Intriguingly, transcripts of cellular retinoic acid binding protein 1 are always found at the interface between dividing and post-mitotic cells.At the rhombic lip, retinoic acid is likely to act as a dorsalising factor in parallel with other roofplate signalling pathways.While its precise role is unclear, retinoic acid is potentially well placed to regulate temporally determined cell fate decisions within the rhombic lip precursor pool.

View Article: PubMed Central - HTML - PubMed

Affiliation: MRC Centre for Developmental Neurobiology, King's College London, 4th floor New Hunt's House, Guy's Campus, London SE1 1UL, UK. leigh.wilson@kcl.ac.uk

ABSTRACT

Background: Human retinoic acid teratogenesis results in malformations of dorsally derived hindbrain structures such as the cerebellum, noradrenergic hindbrain neurons and the precerebellar system. These structures originate from the rhombic lip and adjacent dorsal precursor pools that border the fourth ventricle roofplate. While retinoic acid synthesis is known to occur in the meninges that blanket the hindbrain, the particular sensitivity of only dorsal structures to disruptions in retinoid signalling is puzzling. We therefore looked for evidence within the neural tube for more spatiotemporally specific signalling pathways using an in situ hybridisation screen of known retinoic acid pathway transcripts.

Results: We find that there are highly restricted domains of retinoic acid synthesis and breakdown within specific hindbrain nuclei as well as the ventricular layer and roofplate. Intriguingly, transcripts of cellular retinoic acid binding protein 1 are always found at the interface between dividing and post-mitotic cells. By contrast to earlier stages of development, domains of synthesis and breakdown in post-mitotic neurons are co-localised. At the rhombic lip, expression of the mRNA for retinoic acid synthesising and catabolising enzymes is spatially highly organised with respect to the Cath1-positive precursors of migratory precerebellar neurons.

Conclusion: The late developing hindbrain shows patterns of retinoic acid synthesis and use that are distinct from the well characterised phase of rostrocaudal patterning. Selected post-mitotic populations, such as the locus coeruleus, appear to both make and break down retinoic acid suggesting that a requirement for an autocrine, or at least a highly localised paracrine signalling network, might explain its acute sensitivity to retinoic acid disruption. At the rhombic lip, retinoic acid is likely to act as a dorsalising factor in parallel with other roofplate signalling pathways. While its precise role is unclear, retinoic acid is potentially well placed to regulate temporally determined cell fate decisions within the rhombic lip precursor pool.

Show MeSH
Related in: MedlinePlus