Raymond Teck Ho Lee1, Jean Paul Thiery1,2,3 and Thomas J. Carney1.
1 - Institute of Molecular and Cell Biology (IMCB), Agency for Science, Technology and Research (A*STAR), Singapore
2 - Department of Biochemistry, Yong Loo Lin School of Medicine, National University of Singapore, Singapore
3 - Cancer Science Institute, National University of Singapore, Singapore
Published in Current Biology, Volume 23, Issue 9, R336-R337, 6 May 2013
During development, neural crest cells disperse throughout the embryonic head to generate diverse cell types of two classes, non-ectomesenchymal (including melanocytes, peripheral neurons and glia) and ectomesenchymal (skeletogenic, odontogenic, cartilaginous and connective tissue cell fates). In contrast to cranial neural crest, trunk neural crest of amniotes generates only non-ectomesenchymal derivatives. Anamniote trunk neural crest, however, has been assumed to generate derivatives of both classes, including osteoblasts of dermal skeletal elements, which includes scales and fin rays. Despite having many direct implications for the fields of neural crest, evolutionary and skeletal biology, this proposal has never been rigorously tested. Through genetic lineage tracing in zebrafish, we present the first test of this proposal and find that trunk neural crest does not appear to generate fin osteoblasts; rather these derive from a late emerging population of paraxial mesoderm during juvenile stages. Similarly we show that the mineralising cells of the scales are mesodermally derived, with no contribution from neural crest. Our data suggest that trunk/tail exoskeletal structures evolved through deployment of mesodermally derived mesenchyme, rather than neural crest
Figure Legend: Fin osteoblasts derive from late immigrating paraxial mesoderm
A-B: Adult (90dpf) sox10:Cre; ubi:switch transgenics showing derivatives in the fin derived from neural crest and sox10 expressing cells. Lateral view of wholemount fin, immunostained to detect mCherry, indicates labelled cells running along the fin rays (A). Superimposing on a brightfield image demonstrates that these run within the lepidotrichia (A′). Magnified view of part of A′ highlights the position within the ray and also mCherry positive melanophores (arrowheads; A″). Transverse cryosection of a sox10:Cre; ubi:switch fin immunostained for mCherry (red) and zns-5 (green) and counterstained with DAPI (blue). mCherry positive cells are concentrated in two bundles within the fin ray and are zns-5 negative (B). C-F′: Adult (90dpf) fins of tbx6:Cre; ubi:switch (C-D′) and tbx6:CreERt2; ubi:switch (E-F′) imaged as lateral wholemounts (C-C′; E-E′) or as transverse cryosections (D-D′; F-F′). Fins have been immunostained for mCherry (red; C-F′) and zns-5 (green; D′, E′, F′) and counterstained with DAPI (blue; D′, F′). (C) is also shown superimposed on the Nomarski image (C′). In both lines, osteoblasts are mCherry positive. G-H: Lateral images of the trunk/tail (G) and dorsal medial fin (H) of 5dpf (G) and 21dpf (H) tbx6:CreERt2; ubi:switch transgenics treated with 4-Hydroxytamoxifen and immunostained for mCherry. Larvae with no labelled cells in the fins at larval stages (G) often were observed to have chains of cells, aligned to forming bony rays, within the fins at 21dpf (arrows; H). I: Counts of mCherry positive cells in the fins during postembryonic development. Secondary immigration was noted from 14dpf. J-K′: Lateral images of scales in 30dpf sox10:Cre; ubi:switch (J-J′) and tbx6:Cre; ubi:switch (K-K’) transgenics immunostained for mCherry (red; J-K′) and zns-5 (green; J′, K′). Co-labelling is only seen in the tbx6:Cre; ubi:switch line.
For more information on Philip INGHAM’s laboratory, please click here.
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