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Here we clone the Xenopus 5-HT2B receptor cDNA and describe its spatio-temporal mRNA expression within the developing larval brain and visual system. Expression of the 5-HT2B transcripts is compared to that of 5-HT2C as well as proliferation and neurogenic markers. In developing brain and retina, 5-HT2B and 2C mRNAs are mainly expressed in proliferative regions. We suggest that these receptors may play a role in the larval secondary neurogenesis by mediating mitogenic effects of serotonin.
Fig. 1. ClustalW alignment of the amino acid sequence of X. laevis 5-HT2B receptor with known homologues (human: Swiss-Prot accession no. P41595; rat (Rattus norvegicus): P30994; mouse (Mus musculus): Q02152; Tetraodon fluviatilis: Q8UUG8). Black boxes indicate amino acid identity, grey boxes amino acid similarity. Note the conserved S/TXV motif at the carboxy-terminus (isoleucine substitutes valine in the rat sequence). The box shading alignment was generated on the BOXSHADE server at www.ch.embnet.org.
Fig. 2. Developmental expression of 5-HT2B receptor mRNA. RT-PCR reactions were carried out with equal amounts of total RNA preparations from the different embryonic and larval stages (as indicated). Ornithine decarboxylase (ODC) amplification was used as control of the reaction (bottom panel). A-RT minus negative control is shown.
Fig. 3. Expression pattern of 5-HT2B and 2C receptor mRNAs in the larval brain. The probes used are indicated at bottom of each panel. The figure shows transversal sections of larvae neural tube at stage 40 (A–C) and 45 (D–O). Panels correspond to diencephalon (D–F), mesencephalon (A–C, G–I); anterior (J–L and O) and posterior rhomboencephalon (M–N). Proliferating zones are evidenced by BrdU incorporation (E,H,K) and by labelling with proliferation markers (B,C,N,O). (E,H,K): in blue, Hoechst nuclear staining; BrdU incorporation is viewed as orange fluorescence.
Fig. 4. Expression of 5-HT2B and 2C receptor mRNAs in developing retina. Transverse sections through the eye of a stage 40 (A–C) and 45 larva (D–I). The probes used are indicated at bottom of each panel. The CMZ is labelled by proliferation markers (B,C,E,F) and stained with anti-BrdU antibody after BrdU incorporation (H). In blue, Hoechst nuclear staining; orange, BrdU incorporation. (G) is an enlargement of (D) to show the scattered postmitotic cells expressing 5-HT2B transcripts in the INL. CMZ, ciliary marginal zone; L, lens; INL, inner nuclear layer.
