Fig. 2. Elevated retinoid signalling increases the number of primary sensory neurons. (A–C). Isl1+ primary sensory neurons at stage 20 in (A) control, (B) RAR/RXR mRNA injected and (C) RAR/RXR mRNA injected + RA treated embryos. The number of neurons increases in embryos subjected to elevated retinoid signalling though the neurons are still found in restricted, if widened, domains and are not dispersed throughout the neurectoderm. Scale bar applies to each panel A–C and represents 60 μm. (D). The ratio of Isl1+ primary sensory neurons on the left compared to the right side of the embryo was calculated for uninjected controls (top panel). Each dot represents an individual embryo. The peak (dark yellow) and distribution ranges (light yellow) of the ratio of Isl1+ primary sensory neurons are indicated. Isl1+ primary sensory neurons were then counted in embryos unilaterally injected with RAR/RXR (middle panel) and RAR/RXR with 10−7 M RA (lower panel). The blue dots represent individual embryos injected with 250–500 pg and red dots individuals with 62-125pg of RNA. Following injection of 250–500 pg of RAR/RXR mRNA most individuals have increased numbers of Isl1+ primary sensory neurons on the injected side. Following RA treatment a larger proportion of embryos have increased numbers of Isl1+ primary sensory neurons on the injected side. In a small number of cases (marked with a † symbol) there is a significant decrease in the number of Isl1+ primary sensory neurons on the injected side of embryos receiving 250–500 pg of RNA. In these cases it appeared as if gastrulation was compromized on the injected side of the embryo. (E–G) Neural specific tubulin expression assayed by wholemount in situ hybridization in (E), control, (F), RAR/RXR mRNA injected and (G), RAR/RXR mRNA injected + RA treated embryos. The three domains of primary neurons either side of the midline are marked in (E), s, sensory, i, inter and m, motor neurons. The expression of NST in the trigeminal ganglion is also marked (tg). (F) the injected side is marked with a red dot and the horizontal bar marks the midline. There is increased NST expression in the sensory neuron and motor neuron domains (black arrows) compared to the uninjected side. However, these domains remain separated by a region of neurectderm that does not express NST (open arrow). (G). Increased NST expression is seen on the injected side of the embryo grown in 10−7 M RA but still does not extend significantly into the non-neural ectoderm or into the region of the neurectoderm between sensory and motor neuron domains (open arrow).
Image published in: Sharpe C and Goldstone K (2000)
Copyright © 2000. Image reproduced with permission of the Publisher, Elsevier B. V.
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