Ancestry of motor innervation to pectoral fin and forelimb
Supplementary Movie 1: Pectoral motoneurons in embryonic midshipman fish, Porichthys notatus. A representative example of fluorescent retrograde labelling from the fin bud showing the location of pectoral motoneurons along the anterior-posterior axis and their alignment with myotomes. (2.404Mb)
Supplementary Movie 2: Alignment of pectoral, precerebellar and hindbrain motor neurons in transgenic zebrafish, Danio rerio. A representative example of double labelling from the fin bud and cerebellum in the isl1-GFP background showing the alignment of pectoral motoneurons with identified hindbrain neuronal subgroups. (961.4Kb)
Supplementary Movie 3: Lineage tracing using the photoconvertable protein Kaede. A representative example of lineage tracing of the neuroepithelium at the level of somite 4–5 (anterior spinal cord) showing that pectoral motoneurons originated in both hindbrain and spinal cord without anterior-posterior migration during early neurogenesis. (2.876Mb)
Bass, Andrew H.
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Motor innervation to the tetrapod forelimb and fish pectoral fin is assumed to share a conserved spinal cord origin, despite major structural and functional innovations of the appendage during the vertebrate water-to-land transition. In this paper, we present anatomical and embryological evidence showing that pectoral motoneurons also originate in the hindbrain among ray-finned fish. New and previous data for lobe-finned fish, a group that includes tetrapods, and more basal cartilaginous fish showed pectoral innervation that was consistent with a hindbrain-spinal origin of motoneurons. Together, these findings support a hindbrain–spinal phenotype as the ancestral vertebrate condition that originated as a postural adaptation for pectoral control of head orientation. A phylogenetic analysis indicated that Hox gene modules were shared in fish and tetrapod pectoral systems. We propose that evolutionary shifts in Hox gene expression along the body axis provided a transcriptional mechanism allowing eventual decoupling of pectoral motoneurons from the hindbrain much like their target appendage gained independence from the head.
© Macmillan Publishers Limited, 2010. This article is distributed under the terms of the Creative Commons Attribution-NonCommercial-No Derivative Works 3.0 Unported License. The definitive version was published in Nature Communications 1 (2010): 49, doi:10.1038/ncomms1045.
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