Identifikation und Charakterisierung von Typ-II-Neuroblasten im Embryo des Mehlkäfers Tribolium castaneum

Identification and characterisation of type II neuroblasts in the embryo of the red flour beetle Tribolium castaneum

by Simon Rethemeier
Doctoral thesis
Date of Examination:2024-08-28
Date of issue:2024-08-16
Advisor:Prof. Dr. Christoph Viebahn
Referee:Prof. Dr. Christoph Viebahn
Referee:Prof. Dr. Gregor Bucher
Sponsor:Jacob-Henle-Programm der Universitätsmedizin Göttingen
Persistent Address: http://dx.doi.org/10.53846/goediss-10679

 

 

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Abstract

English

Evolution has created a wide range of morphological diversity in insect brains, while the basic structure is conserved. Little is known about the mechanisms that lead to this evolutionary diversification of similar structures. The central complex, one of these neuropiles, shows evolutionary heterochrony: While the hemimetabolious grasshopper Schistocerca gregaria builds up this whole structure during the embryonic period, the highly derived holometabolous fruit fly Drosophila melanogaster develops it mainly in the late larval and pupal stages. Neurogenesis in insects is carried out by neuroblasts. Most of the insect nervous system is build up by type I neuroblasts but for central complex development in Drosophila and Schistocerca also type II neuroblasts have been discovered. Those have the ability to produce more progeny by generating intermediate progenitor cells. Regarding to the central complex development, the red flour beetle Tribolium castaneum shows an intermediate position by building up an immature but already functional version of this neuropil in the late embryo. Using mRNA in situ hybridisation and antibody staining on transgenic lines that mark distinct genes, this work identified actively proliferating cell lines produced by type II neuroblasts in the Tribolium embryo that take part in the embryonic central complex genesis. A high degree of conservation could be shown, especially regarding their dorsomedial position in the embryonic head and their characteristic gene expression pattern, which appears homologous to the situation in Drosophila. However, the unexpected finding that Tribolium generates nine type II neuroblasts, while only eight could be found in Drosophila and Schistocerca, combined with the fact that Tribolium embryonic type II lines could be characterised as containing significantly more cells than those in Drosophila leads to the conclusion that embryonic type II neuroblasts seem to be a factor for the relatively earlier central complex development in Tribolium. Regarding this, type II neuroblasts appear also as an interesting model for further studies on heterochrony during insect brain development.
Keywords: Tribolium castaneum; Tribolium; type I neuroblast; type II neuroblast; central complex; pointed; fez; neuroblast; heterochrony; neurogenesis; embryo; insect; nervous system; evolution; intermediate progenitor cell; ganglion mother cell; deadpan; asense
Schlagwörter: Centralcomplex; Typ-I-Neuroblast; Typ-II-Neuroblast; Heterochronie; Neurogenese; Insekt; Nervensystem; Evolution