The evolution and development of light detecting organs are a field of high controversy. The theory of the same origin stands against that of multiple parallel origins. In order to learn more about the evolution of visual systems different developmental and morphological aspects are important to consider.
As the spider Parasteatoda tepidariorum has two different eye types it is an ideal model organism to study the development of those systems. The morphological differences between the two optic systems of P. tepidariorum are easy to detect. The main eyes are pure black and embossed whereas the other three eye pairs are flat and equipped with a tapetum which reflects entering light. However, so far it is not known if there is a developmental difference between those eye types as well. A lot of well known and highly conserved eye markers, like pax6, can also be found in the spider.
One aim of this thesis was to figure out if a second pax6 gene and orthologs to eyegone (eyg), another gene belonging to the PAX family, and twin of eyegone (toe) respectively can be found in P. tepidariorum. The second aim was to verify the theory of Paulus (1979) who claimed that the main eyes of spiders are homologs to the ocelli of insects. For this reason I searched the spider transcriptome for the ocelli-specific genes noc ocelli (noc) and reduced ocelli (rdo).
With the help of sequence similarity search and phylogenetic tree construction I was able to find a second pax6 gene and orthologs to eyg and noc. No orthologs for toe and rdo could be found.
To further examine the genes Pt-eyg and Pt-noc RNA probes for in-situ hybridization were synthesized. As a specific marker for the embryonic ocular region, Pt-Wnt5 was successfully established as probe for double in-situ hybridizations.
Although some specific staining occurs using the Pt-eyg probe, no specific expression in the ocular region or in the head could be observed. The lack of specific staining in the ocular region might indicate that eyg plays no role in the eye development of P. tepidariorum.
The in-situ hybridization with Pt-noc reveals an interesting expression pattern. The expression of Pt-noc starts at embryonic stage 6 and shows partly co-localization with Pt-pax6 starting at stage 7.
In addition, to analyze the function of the gene six3.1 during the development parental RNA interference (RNAi) was performed. The analysis is still in progress but preliminary results do not show influences during the development of the embryos.