Report on the 2nd international molecular biosciences PhD and postdoc conference 2023: The emerging challenge - environmental impacts on human health.

The 2nd International FEBS-IUBMB-ENABLE Molecular Biosciences PhD and Postdoc Conference was held from 23rd to 25th November 2023 in Cologne, Germany. Over 240 participants from 31 different countries came together at the University of Cologne to follow the two-day scientific symposium and the career day. This year's topic was "The emerging challenge - environmental impacts on human health". In four different sessions, eight renowned keynote speakers presented their current research. By offering flash and short talks, 39 participants were able to present their work in front of a big audience. Scientific exchange and networking were encouraged during the two poster sessions, during breaks, and the conference dinner. On the Career Day, a career fair was held and participants could attend workshops as well as career chats to improve their job prospects. The success of the series will be continued during the next conference edition: "Artificial Intelligence - Reshaping biomedical and healthcare research", which will take place 4th to 6th December 2024 in Singapore.

Specialized ommatidia of the polarization-sensitive dorsal rim area in the eye of monarch butterflies have non-functional reflecting tapeta.

Many insects exploit sky light polarization for navigation or cruising-course control. The detection of polarized sky light is mediated by the ommatidia of a small specialized part of the compound eye: the dorsal rim area (DRA). We describe the morphology and fine structure of the DRA in monarch butterflies (Danaus plexippus). The DRA consists of approximately 100 ommatidia forming a narrow ribbon along the dorsal eye margin. Each ommatidium contains two types of photoreceptor with mutually orthogonal microvilli orientations occurring in a 2:6 ratio. Within each rhabdomere, the microvilli are well aligned. Rhabdom structure and orientation remain constant at all retinal levels, but the rhabdom profiles, as seen in tangential sections through the DRA, change their orientations in a fan-like fashion from the frontal to the caudal end of the DRA. Whereas these properties (two microvillar orientations per rhabdom, microvillar alignment along rhabdomeres, ommatidial fan array) are typical for insect DRAs in general, we also report and discuss here a novel feature. The ommatidia of monarch butterflies are equipped with reflecting tapeta, which are directly connected to the proximal ends of the rhabdoms. Although tapeta are also present in the DRA, they are separated from the rhabdoms by a space of approximately 55 mum effectively inactivating them. This reduces self-screening effects, keeping polarization sensitivity of all photoreceptors of the DRA ommatidia both high and approximately equal.

Homothorax switches function of Drosophila photoreceptors from color to polarized light sensors.

Different classes of photoreceptors (PRs) allow animals to perceive various types of visual information. In the Drosophila eye, the outer PRs of each ommatidium are involved in motion detection while the inner PRs mediate color vision. In addition, flies use a specialized class of inner PRs in the "dorsal rim area" of the eye (DRA) to detect the e-vector of polarized light, allowing them to exploit skylight polarization for orientation. We show that homothorax is both necessary and sufficient for inner PRs to adopt the polarization-sensitive DRA fate instead of the color-sensitive default state. Homothorax increases rhabdomere size and uncouples R7-R8 communication to allow both cells to express the same opsin rather than different ones as required for color vision. Homothorax expression is induced by the iroquois complex and the wingless (wg) pathway. However, crucial wg pathway components are not required, suggesting that additional signals are involved.