University of Western Ontario - Electronic Thesis and Dissertation Repository

Degree

Master of Science

Program

Anatomy and Cell Biology

Supervisor

Lynne-Marie Postovit and Peeyush Lala

Abstract

The human placenta develops from highly proliferative and phenotypically plastic cells called trophoblasts. Bi-potential trophoblast stem cells differentiate into the villous pathway to form the syncytiotrophoblast layer and the extravillous trophoblast (EVT). The HTR-8/SVneo cell line is widely used to study trophoblast biology. These cells variably express villous-specific or EVT-specific genes depending on conditions. Such phenotypic plasticity is indicative of a bi-potential cytotrophoblast progenitor. Preliminary work has shown that similar to progenitors in situ, a subpopulation of HTR-8/SVneo cells expresses a6b4 integrin. This a6b4high subset exhibits enhanced clonogenicity and differentiation capacity. This cell line also expresses Nodal, a stem cell-associated factor that sustains the pluripotency of embryonic stem cells and is re-expressed in certain cancers. I hypothesized that the a6b4high subset within HTR-8/SVneo is enriched with bi-potential cytotrophoblast progenitor-like cells that are maintained by Nodal signaling. Our results revealed that the a6b4high subset expresses greater amounts of Nodal protein relative to the a6b4low subset. To investigate the role of Nodal in regulating trophoblast progenitors, stable Nodal knock-down and over-expressing cells were analyzed. It was found that Nodal is required for clonogenicity, maintenance of enhanced a6b4 expression and endovascular differentiation along the EVT pathway. These results suggest that the a6b4high population may represent a villous cytotrophoblast progenitor cell in which Nodal regulates clonogenicity and capacity for differentiation along the EVT pathway.