Advisor: Tim Wollesen

Master's Defensio

Friday, November 29th, 2024, 13:15 am CET
SR 1.2, UBB
Djerassiplatz 1, 1030 Vienna

Abstract

In many different phyla of multicellular animals (Metazoa), apical organs are present during ontogeny. The apical organ consists of a ciliary tuft and receptor cells, and is connected to the remaining nervous system via a network of neurites. Due to its anatomy and its location in the anterior part of the larva, it is assumed to play a sensory role during locomotion, metamorphosis, and settlement. In the chaetognath Spadella cephaloptera, a direct developer without a larval stage, an apical organ has not yet been described.
In this Master's thesis, the expression patterns of genes in S. cephaloptera that are expressed in the apical organs of metazoans were studied, such as fezF, foxG, foxJ1, and syt1. Phylogenetic analyses confirmed the identity of all the aforementioned genes, and in situ hybridization experiments were conducted at different developmental stages.
FezF is expressed in the ventral nerve cord, a part of the central nervous system, of hatching S. cephaloptera. Additionally, fezF is expressed in a triangular-shaped region in the brain. The expression of foxG is visible in the anteroventral region of the cerebral ganglia in S. cephaloptera. FoxJ1 is expressed in two symmetrical regions of the lateral plates in S. cephaloptera. Syt1 is strongly expressed in the ventral nerve cord of S. cephaloptera.
In summary, two of the four aforementioned genes are expressed in the anterior nervous system during the development of chaetognaths, but not in a structure resembling an apical organ. The absence of an apical organ-like structure in chaetognaths, despite conserved gene expression, suggests that the apical organ may either be an ancient structure of Bilateria that was lost in the Gnathifera, or that it may have independently evolved in other bilaterian lineages.