Nervous picket fences
نویسنده
چکیده
omplex nervous system patterning—usually assumed to have coevolved with advanced, centralized nervous systems— may have arisen before nerves consolidated into a central nerve chord, according to Christopher Lowe, John Gerhart (University of California, Berkeley, CA), Marc Kirschner (Harvard Medical School, Boston, MA), and colleagues. Their idea runs counter to the prevailing theory of dorsoventral axis inversion. The ventral nerve chords in arthropods (such as Drosophila ) and dorsal nerve chords in chordates (such as humans) have been thought to be related via an inversion event some time during evolution. In the new theory, however, the original ancestor is proposed to have had a dispersed nervous system that converged centrally in independent dorsal and ventral events. Reconstructing chordate evolution is tricky for several reasons. The rapidity of the Cambrian explosion and the soft bodies of the ancestors of chordates make it impossible to construct precise evolutionary trees. And chordates’ closest major relatives, the echinoderms, have added so many bizarre anatomical features that they are next to useless for comparisons. Thus, the new study subject is the acorn worm. These hemichordates are a lesser-known lineage but, like the chordates, they are bilateral deuterostomes, in contrast to arthropods, which are protostomes and thus more distantly related. The basic result of the new paper is simple. Although acorn worms have distributed nerve nets rather than nerve chords, they C
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ورودعنوان ژورنال:
- The Journal of Cell Biology
دوره 162 شماره
صفحات -
تاریخ انتشار 2003