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Published September 1993 | Published
Journal Article Open

XASH-3, a novel Xenopus achaete-scute homolog, provides an early marker of planar neural induction and position along the mediolateral axis of the neural plate


We have isolated a novel Xenopus homolog of the Drosophila achaete-scute genes, called XASH-3. XASH-3 expression is neural specific and is detected as early as stage 11 1/2, making it one of the earliest markers of neural induction so far described. Moreover, XASH-3 expression within the neural plate is regionally restricted. Transverse bands of XASH-3 mRNA mark discrete positions along the anteroposterior axis, while longitudinal bands mark a discrete position along the mediolateral axis. This latter site of XASH-3 expression appears to demarcate the prospective sulcus limitans, a boundary zone that later separates the functionally distinct dorsal (alar) and ventral (basal) regions of the spinal cord. In sandwich explants lacking any underlying mesoderm, XASH-3 is expressed in longitudinal stripes located lateral to the midline. This provides the first indication that planar or midline-derived inductive signals are sufficient to establish at least some aspects of positional identity along the mediolateral axis of the neural plate. By contrast, the transverse stripes of XASH-3 expression are not detected, suggesting that this aspect of anteroposterior neural pattern is lost or delayed in the absence of vertically passed signals. The restricted mediolateral expression of XASH-3 suggests that mediolateral patterning of the neural plate is an early event, and that this regionalization can be achieved in the absence of inducing signals derived from underlying mesoderm.

Additional Information

© 1993 by Company of Biologists. (Accepted 22 June 1993) The authors are particularly grateful to Drs Beatriz Ferreiro, William Harris and Chris Kintner for providing cDNA libraries, technical advice and scientific discussion. The authors would also like to thank Drs Akiko Kumagai, Bill Dunphy, Paul Skoglund and Ariel Ruiz i Altaba for sharing their technical expertise at various stages of this project. We especially thank Dr Scott Fraser for support (grant HD 29304) and the use of his laboratory facilities. We also thank Drs David Wilkinson and Chris Kintner for providing the Xenopus Krox-20 and N-CAM probes respectively, David Turner for sharing his results prior to publication, and Adam Strassberg for help with computer graphics. The authors are also grateful to Drs Ariel Ruiz i Altaba and Tom Jessell for many helpful discussions, and to Bill Harris, Tom Jessell, Barbara Wold and Scott Fraser for their critical comments on the manuscript. K.Z. was supported by an NIH post-doctoral fellowship and is currently an Associate of the Howard Hughes Medical Institute. D.J.A. is an Associate Investigator of the Howard Hughes Medical Institute.

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