Neue Funktionen des Drosophila Hox Gens Ultrabithorax in der Entwicklung des zentralen Nervensystems
Entwicklungsbiologie
Zusammenfassung der Projektergebnisse
One major goal of this project was to determine how Hox genes pattern regional differences in the central nervous system, with a particular focus on post-mitotic, i.e. differentiating neurons. The second goal was to clarify how the functional specificity of these broadly expressed proteins is regulated at the molecular and cellular level. Hox genes are known to specify motoneuron pools in the developing vertebrate spinal cord and to control motoneuronal targeting in several species. However, the mechanisms controlling axial diversification of muscle innervation patterns are still largely unknown. Our data showed that the Drosophila Hox gene Ultrabithorax (Ubx) acts in the late embryo to establish target specificity of ventrally projecting RP motoneurons. In abdominal segments A2 to A7, RP motoneurons innervate the ventrolateral muscles VL1-4, with VL1 and VL2 being innervated in a Wnt4-dependent manner. In Ubx mutants, these motoneurons fail to make correct contacts with muscle VL1, a phenotype partially resembling that of the Wnt4 mutant. We showed that Ubx regulates expression of Wnt4 in muscle VL2 and that it interacts with the Wnt4 response pathway in the respective motoneurons. Ubx thus orchestrates the interaction between two cell types, muscles and motoneurons, to regulate establishment of the ventrolateral neuromuscular network. We furthermore showed that the RP3 motoneuron also requires Ubx for correct pathfinding, and that Ubx regulates expression of the Netrin B (NetB) signalling molecule in ventrolateral muscles VL3/4. This regulation and the NetB receptor frazzled in the RP motoneurons are required for correct innervation of muscles VL3/4 by motoneuron RP3. In the second part of the project, we collaborated with Prof. P. Beli (IMB Mainz and University of Mainz) to identify post-translational modifications (PTMs) on and proteins complexing with the Ubx protein by means of liquid chromatography coupled to tandem mass spectrometry. We found that Ubx can be acetylated at at least five lysines and that phosphorylation can take place at at least 4 sites. We focused on acetylation to show that it can affect the stability and transcriptional activity of Ubx, at least in the specific contexts we investigated. Furthermore, the results of our in vivo experiments with ectopic expression of acetylation-deficient Ubx proteins showed that only specific functions such as activation of neuronal apoptosis are affected by individual acetylation sites, while others, such as transformation of denticle belts are not. We also showed that Ubx complexes with Sirtuin 2 (Sir2), a (NAD+)-dependent deacetylase, suggesting that Sir2 may be involved in Ubx deacetylation. Taken together our data support our hypothesis that PTMs affect Ubx function and may thus contribute to functional diversity of Hox proteins.
Projektbezogene Publikationen (Auswahl)
- (2017). The Drosophila Hox gene Ultrabithorax acts both in muscles and motoneurons to orchestrate formation of specific neuromuscular connections. Development 144,139-150
Hessinger, C., Technau, G.M. and Rogulja-Ortmann, A.
(Siehe online unter https://doi.org/10.1242/dev.143875)
