Amirthalingam, G.S.; (2008) Signalling mechanisms which are involved in the establishment of Hoxb4 expression in the chick neural tube. Doctoral thesis , University of London.

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Abstract

Assignment of antero-posterior (AP) positional identity along the neuraxis is regulated by the Hox gene family. In order to establish the precise expression domains of Hox genes, a number of transcription factors and signalling molecules are required. Previous studies have implicated the involvement of vertical and planar signalling in the assignment of positional identity. However, it remains unclear to what extent vertical and planar signalling contribute to correct AP patterning and whether any competence differences exist along the dorso-ventral axis of the neural tube that may bias Hox induction. This study examines how various signalling mechanisms are involved in patterning the chick neural tube along its AP axis, using Hoxb4 as an axial marker. This work shows that signals from somites (vertical signals) are required but not sufficient to establish the correct expression pattern o HoxM in the neural tube thus indicating the need for additional signals emanating from more posterior tissue. Experiments conducted in order to elucidate the exact nature of these signals imply that they are planar signals. In addition, this work shows that the dorsal side of the neural tube is more responsive to the somite signal than the ventral side. This responsiveness seems to be caused by the action of BMPs in the dorsal neural tube. Therefore, it appears that BMP and the somite signal may work in conjunction to upregulate Hoxb4 expression in the neural tube.

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