Functional importance of novel translated regions during development

It has generally been assumed that most proteins with important functions during embryogenesis have already been identified. However, scientists recently discovered that many regions in our genome are engaged by the cellular machinery that is responsible for making proteins. Several of these translated regions were predicted to encode short proteins that stand out by being conserved between organisms as distant as flies and human. Such a level of conversation suggests that they have important functions, but since these newly discovered proteins are all small in size they have escaped previous detection. The majority of newly discovered translated regions, however, lacks signatures of protein conservation and has been suggested to have regulatory roles, yet its function during normal development is unclear. The primary goal of this project is to gain insights into the functional impact that these newly discovered translated regions have whether coding or regulatory. We are particularly interested in unravelling functions during embryogenesis and therefore use zebrafish, and ideal model for vertebrate early development, as model system. One the one hand we will investigate the function and mechanism of one particular short protein that we recently discovered. This protein turns out to have a highly interesting phenotype, namely sperm can no longer enter the egg, giving rise to a fully penetrant block in fertilization. Our studies will aim to uncover the function and mechanism of this little yet so important protein during one of the most fundamental yet enigmatic processes in an organisms life. On the other hand, we will tackle the question regarding regulatory translation by investigating its impact on developmental transitions. Overall, this project will employ a combination of molecular, genetic, cell biological, state-of-the-art imaging, genomics and computational approaches. Since the roles of the majority of novel translated regions are unknown, these studies will provide major advances to our understanding of this fascinating class of genetic elements.

The goal of our research was to gain mechanistic insights into the egg-to-embryo transition. Over the past 6 years, we have made key advances in the two areas we wanted to focus as part of the START grant: (1) fertilization, and (2) regulatory mechanisms during the egg-to-embryo transition. New insights into the molecular mechanism of fertilization Our initial discovery of the first essential fertility factor in fish, Bouncer, and its role in species-specific fertilization established fertilization as a new research direction and major focus in my lab. Over the past years, we have continued to expand our knowledge of essential vertebrate fertility factors. Most excitingly, we recently discovered a conserved trimeric fertilization complex present on vertebrate sperm. This complex is composed of the two known fertility factors Izumo1 and Spaca6, and the previously uncharacterized transmembrane protein Tmem81, which we also showed to be essential for male fertility in both fish and mice. In addition, we discovered that this trimeric complex on sperm interacts with different receptors on the egg surface - JUNO in mammals and Bouncer in fish. Thus, vertebrate fertilization provides an intriguing example of conserved sperm factors interacting with evolutionary distinct egg receptors to mediate sperm-egg binding. Dormancy of egg ribosomes Prior to fertilization, eggs of many organisms are in a dormant state, meaning processes including translation are repressed despite of the fact that eggs contain vast numbers of maternal components, including ribosomes. To address how dormancy is controlled and how eggs store maternal ribosomes, we used a combination of cryo-EM structural analyses, in vivo functional assays and in vitro studies to uncover a conserved, previously unknown dormant egg ribosome state that preserves ribosomes and prevents premature translational activation. Our study revealed a developmentally programmed, conserved ribosome state important for ribosome storage and translational repression.