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Hindbrain patterning involves graded responses to retinoic acid signalling

Valérie Dupé and Andrew Lumsden*

MRC Centre for Developmental Neurobiology, King’s College London, Guy’s Campus, London SE1 1UL, UK



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  		Fig. 1. BMS493, a retinoid antagonist, treatment impairs hindbrain development in a stage-dependant manner. Dorsal view of whole-mounts (a-c,g-k,m-q) or flat-mounted hindbrains (d-f,l) of control (h,I,k,n) and antagonist-treated (5x10-6 M) chick embryos at stage 5 (a,j,k), stage 6 (b,m), stage 6+ (c-e,n), stage 7 (f), stage 7+ (g), stage 8- (p) and stage 9 (q). The embryos were collected after approximately 24 hours of culture and the expression of Krox-20 (a-d,f-h, stage 11), MafB/kr (e,i,j, stage 9), Hoxb1 (k-n, stage 11) and follistatin (o-q, stage 12) was analysed. Stages indicated at the bottom-right of the pictures correspond to the stage of treatment. s1, first somite; s6, sixth somite; r4-r7, rhombomeres 4 to 7.

 


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  		Fig. 2. Establishment of hindbrain boundaries is dependent on retinoic acid concentration. Dorsal view of whole-mounts of BMS493-treated chick embryos at stage 5 at the following concentration: 10-6 M (a,g), 5x10-7 M (b,c,j,l), 2.5x10-7 M (d), 10-7 M (e,h,m) and 10-8 M (f,i,k,n). Whole-mount in situ hybridization was performed on embryos using digoxigenin-labelled probes for Krox-20 (a-f, stage 11), Hoxb1 (g-i, stage 11), MafB/kr (j,k, stage 10) and follistatin (l-n, stage 12). s6, sixth somite. r4-r7, rhombomeres 4 to 7.

 


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  		Fig. 3. In retinoic acid-deficient chick embryos, r4 forms a defined domain from the r3/r4 border to the level of the sixth somite. Dorsal view of whole mounts of control embryos (a,c,e) and BMS493-treated (5x10-6 M) chick embryos (b,d,f). In treated embryos, follistatin expression is ectopically expressed in the neural tube (b, stage11), Wnt8c expression is not restricted to the normal position of r4 (compare d with c, stage8+) and Cepu-1 expression is throughout the posterior hindbrain (f, stage10). r3, r4, rhombomeres 3 and 4. s1, s6, first somite and sixth somite.

 


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  		Fig. 4. Downregulation of Hoxa1 in BMS493-treated embryos. Dorsal view of whole mounts of control (a) and antagonist-treated (5x10-6 M) chick embryos at stage 4 (b). Note the downregulation of Hoxa1 in its anterior domain of expression in b. Arrows indicate the normal rostral limit of Hoxa1 expression.

 




© The Company of Biologists Ltd 2001