Why is the endometrium such a poorly understood tissue?
I think it’s a bit of everything. First of all, funding. For a long time, and even now, it's not been a high enough priority. But it should be, as it’s absolutely vital for pregnancy and human reproduction, and also underlies many diseases. Endometriosis, where endometrial-like tissue grows outside of the uterus, is a painful condition that affects one in ten women, and endometrial cancer is also quite a common cancer where treatment can cause infertility.
Second is the complexity of the tissue in time and space. During the menstrual cycle it undergoes dynamic cycles of shedding, regeneration and differentiation under the control of hormones, with dramatic changes in architecture happening over the span of days. The outermost lining of the uterus is an epithelium that initially exists as a flat layer of cells. It expands in the proliferative phase, and then invaginates to form glands in the secretory phase – where hormones are released - before shedding and starting again. In that sense the endometrium is like a developmental tissue that constantly changes, and that brings its own challenges but also makes it incredibly interesting for me.
Thirdly, it’s an inaccessible tissue, and you cannot use mice to study it. While we do have laboratory models like the endometrial organoids [human cells grown in the laboratory to represent the tissue], these are still very new. In fact the discoveries we made, relied on a combination of these organoids, single cell RNA sequencing technologies, and spatial transcriptomics. It might not have been possible even ten years ago.