HoxB genes regulate neuronal delamination in the trunk neural tube by controlling the expression of Lzts1.

Differential Hox gene expression is central for specification of axial neuronal diversity in the spinal cord. Here, we uncover an additional function of Hox proteins in the developing spinal cord, restricted to B cluster Hox genes. We found that members of the HoxB cluster are expressed in the trunk neural tube of chicken embryo earlier than Hox from the other clusters, with poor antero-posterior axial specificity and with overlapping expression in the intermediate zone (IZ). Gain-of-function experiments of HoxB4, HoxB8 and HoxB9, respectively representative of anterior, central, and posterior HoxB genes, resulted in ectopic progenitor cells in the mantle zone. The search for HoxB8 downstream targets in the early neural tube identified the Leucine Zipper Tumor Suppressor 1 gene (Lzts1), whose expression is also activated by HoxB4 and HoxB9. Gain and loss of function experiments showed that Lzts1, expressed endogenously in the IZ, controls neuronal delamination. These data collectively indicate that HoxB genes have a generic function in the developing spinal cord, controlling the expression of Lzts1 and neuronal delamination.