From the stem cell to the follicle: Spatial transcriptomics in the ovary to investigate the developmental microenvironment of oocyte production

• Applicant: Professor Dr. Jan Philipp Junker
• Subject Area: Developmental Biology
• Term: since 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 540370162

A major question in biology is how stem cells construct lineages of differentiating cells, and how they are maintained to build organs in development or repair them during homeostasis. Germline stem cells (GSC) produce differentiating oocytes through the process of oogenesis, which is requisite for fertility and reproduction. Our main goal in the proposed project is to understand the regulation and maintenance of GSCs in the ovary, which despite great biomedical importance is poorly understood in vertebrates. In mammals, GSCs are not maintained in the post-fetal ovary, creating an experimental barrier to investigating their regulatory mechanisms and to identifying the missing factors for potentially maintaining GSCs in the ovary. By contrast, in zebrafish, GSCs and their production of eggs through the conserved oogenesis program are maintained throughout life. We propose to exploit this advantage of the zebrafish ovary model and use this unique opportunity to investigate female GSCs in a vertebrate context. Strikingly, for the first time in vertebrates, our preliminary data uncover a potential developmental microenvironment for oocyte production from the GSC to the follicle. We hypothesize that such a microenvironment coordinates spatial and temporal regulatory interactions to maintain GSCs and control early oocyte differentiation. Aiming to understand these regulatory interactions in the ovarian GSC niche, we will take an interdisciplinary approach by applying cutting-edge experimental and computational strategies. We will use single-cell transcriptomics to identify germ cell states and somatic cell types in the ovary, and we will employ spatial transcriptomics to reconstruct the developmental microenvironment in 3D. This analysis will allow us to systematically identify cell-cell interactions in the GSC niche. Importantly, we will combine these systems biology approaches with functional analyses by methods from the fields of cell biology and genetics. Specifically, we will genetically determine GSC lineages, and we will characterize GSC dynamics in real time by time-lapse imaging. Finally, we will perform functional perturbation experiments in long-term ovarian culture to validate regulatory mechanisms of GSC maintenance. To bring our ambitious research goals to fruition, the project will combine the expertise of the Junker lab (MDC Berlin) in single-cell genomics with the expertise of the Elkouby lab (Hebrew University, Jerusalem) in cell and developmental biology of early oogenesis. Thus, our joint efforts will allow us to uncover mechanisms of GSCs maintenance and their production of oocytes in vertebrates, and pave the way to new lines of future investigation. Our proposed research has great potential to produce far-reaching implications to human female reproduction and health, including those needed for female reproductive regenerative medicine.

• DFG Programme: Research Grants
• International Connection: Israel
• International Co-Applicant: Dr. Yaniv Elkouby