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In Xenopus, three neural-specific elav-like genes (ELGs) have been identified, elrB/Xel-1, elrC and elrD. With the aim to highlight possible differences in the regulation of these genes, we compared their expression patterns during development. We had previously shown that elrB is expressed from the early tailbud stage onwards, in both the central and peripheral nervous system. Here we show that both elrC and elrD are expressed earlier than elrB in the developing neural tube and the cranial ganglia, with different temporal specificities. Double in situ hybridizations on brain cross-sections allowed us to define precisely the expression domains of elrB, elrC and elrD in the brain at the tailbud stage. What emerges from this study is a differential distribution of ELGs transcripts in the hindbrain. Also, double labeling with a motor neuron marker shows that in stage 41 tailbud embryos, elrD remains strongly expressed in motor neurons whereas elrC is mostly expressed in non-motor neuron cells.
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10473128
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Fig. 1. Developmental patterns of elrC and elrD expressions. Whole mount in situ hybridizations of elrC (A±G) and elrD (H±K). (A) Stage 12, dorsal view: elrC is expressed in longitudinal stripes (arrows), parallel to the anteriorposterior axis, corresponding to primary neurons. (B) Stage 14, dorsal view. The primary neurons (arrows) and the trigeminal placodes (arrowhead) are labeled. Stage 17, dorsal (C) and anterior (D) views: the neural tube (arrow), the trigeminal placodes (arrowhead) and the olfactory placodes (red arrow) are labeled. Stage 20, dorsal (E) and anterior (F) views: in addition to the neural tube (arrow) and the olfactory placodes (red arrow), the developing cranial ganglia (arrowhead) are also labeled. (G) Stage 32, lateral view: elrC transcripts accumulate in the spinal cord, the brain and the cranial ganglia (arrowheads). Stages 17 (H) and 20 (I), dorsal views: elrD expression is detected in the neural tube (arrow). (J) Stage 20, anterior view. The neural tube (arrow), the trigeminal placode (arrowhead) and the olfactory placodes (red arrow) are labeled. (K) Stage 32, lateral view: elrD transcripts are found in the spinal cord, the brain and the cranial ganglia (arrowheads). In all dorsal views anterior is to the right. After whole mount in situ hybridization of elrC (L) or elrD (M), stage 18 embryos were sectioned. Expression of elrC and elrD in the neural tube are similar. Scale bar, (A±K) 300 um, (L,M) 60 um.
Fig. 2. Comparison of ELGs expressions in the brain. Double in situ hybridizations. (A-I) Double in situ hybridizations were performed on sections of stage 40 Xenopus embryos at the level of the brain. Expressions of elrC (dark blue) and elrD (red) are compared on the same section of the hindbrain (A-C) and at the level of the pineal gland (D-F). (A,D) elrC is mainly expressed in the ventricular zone and in the dorsal region of the brain. (B,E) elrD expression is found in the cortical plate, most strongly in the ventral part, and in the pineal gland (arrow in E). (C,F) Double exposure: where elrD is strongly expressed, elrC is expressed at a low level and conversely where elrC is most strongly expressed, elrD is not detected. For instance, elrD is expressed in the pineal gland (arrow) whereas elrC is not (F). (G-I) elrD (dark blue) and elrB (red) expressions on the same section of the hindbrain. elrD (G) and elrB (H) are both expressed in the cortical plate, and most strongly in the ventral part. (I) Double exposure: elrB and elrD expression domains largely overlap. (J-O) Comparison of ELGs and islet-1 expressions. In situ hybridizations for elrD, elrC and elrB (dark blue staining), followed by immunohistochemistry using anti-islet-1 antibody (red staining), were performed on cryostat brain sections of stage 40 Xenopus embryos. Islet-1 positive cells are present in the most ventral part of the cortical plate (K, M, O, arrow). Faint cytoplasmic dorsal red labeling reflects non-specific staining. (J,K) Comparison of elrD and islet-1 expressions on the same section of the midbrain. elrD expression domain overlaps that of islet-1, however elrD domain is broader and extends more dorsally. (L,M) Comparison of elrC and islet-l expression on the same section of the midbrain. Note that a low level of elrC transcripts (L) in the ventral region of the cortical plate correlates with expression of islet-1 (M). (N and 0) Comparison of elrB and islet-1 expression on the same section of the midbrain. elrB is expressed, albeit at a low level, in the ventral region of the cortical plate (N). The most ventral expression of elrB partially overlaps that of islet-1. Scale bar, 30 um.
