EvoLunch Seminar: Margarida Cardoso-Moreira (Francis Crick Institute)

How do new cells, new tissues, and entire new organs arise during evolution? Our lab investigates these questions using an organ that has evolved independently many times and is remarkably diverse: the placenta. The placenta forms through the fusion of embryonic and maternal tissues, enabling the transfer of nutrients, gases, waste, and more during gestation. In placental species, such as mammals, the mother gestates her offspring inside her body and nourishes them via a placenta. Remarkably, placentas have evolved more than 100 times independently among vertebrates, including once in mammals. Within a family of small live-bearing fishes known as Poeciliidae, at least nine independent origins of the placenta have occurred. This makes them excellent models for studying how new organs emerge during evolution. We have combined whole-genome sequencing, single-cell RNA sequencing, spatial transcriptomics, and imaging to uncover the genetic and developmental basis of five independent origins of a placenta in Poeciliids. Our research revealed that the evolution of a novel cell type unique to Poeciliids allowed this family to transition from egg-laying to live-bearing through egg retention. This new cell type was subsequently co-opted to make up the bulk of the placenta in the five placental species. Our work illustrates the diverse genetic and developmental paths underlying the evolution of new organs, even among closely related species, and supports a link between cell-type innovation and the origin of new organs.