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Fig. 2. Expression patterns of N-CAM-PSA in the CNS of normal and RA-treated embryos shown at the early (stage
~32-36; A-C) and late (stage —45; D, E) tadpole stages after application of RA at the early neurula stage. (A) Overall
staining pattern of N-CAM-PSA showing the subdivisions of the developing CNS. Note the differential labelling within the
major brain regions, especially the hindbrain where alternating levels of N-CAM-PSA in adjacent rhombomeres reveal the
segmental organization of the hindbrain. The transition at the midbrain-hindbrain junction from cells expressing high levels
of N-CAM-PSA to cells expressing low levels is also pronounced (arrow). (B) N-CAM-PSA immunoreactivity in the CNS
of an embryo treated with an intermediate concentration of RA shows a reduction in the size of the anterior regions of the
CNS including a compressed region with intense labelling which corresponds to the hindbrain (bracket). Fewer segmental
subdivisions can be detected in the hindbrain. (C) Pattern of labelling of mAb 5A5 in an embryo treated with a high
concentration of RA. Note the small anterior regions of the CNS and the reduced hindbrain (bracket). In all cases, the
differential expression of N-CAM-PSA at the midbrain-hindbrain junction is maintained (arrows in panels A-C).
(D) Normal expression of N-CAM-PSA in the anterior region of a late tadpole stage (stage ~45) embryo. Note the
reduced expression of N-CAM-PSA in the rhombomeres and midbrain when compared with the embryo shown in panel A.
At this stage, N-CAM-PSA is also expressed in the cranial nerves. (E) Expression of N-CAM-PSA in the CNS of a late
tadpole (stage —45) embryo treated at the neurula stage with an intermediate concentration of RA, showing the absence of
divisions and the reduced size of the brain. Cranial nerves appear to be absent, as judged by the lack of N-CAM-PSA
labelling. C, cerebellar anlage; FB, forebrain; HB, hindbrain; MB, midbrain; N, normal untreated control embryos; o, otic
vesicle; RA, embryos treated with RA at intermediate (I-RA) or high (H-RA) concentrations; SC, spinal cord; arabic
numbers indicate the approximate positions of the different rhombomeres; roman numerals refer to the different cranial
nerves; brackets depict domains of intense labelling corresponding to the hindbrain. Scale bar=0.5mm. Scale bars in
panels A and D are valid for panels A-C and D-E, respectively. |
