Mammary gland biology: stem cells and breast cancer
The mammary gland is a remarkably dynamic tissue. It undergoes rapid outgrowth
and branching morphogenesis during puberty, side branching under the influence of cycling hormone levels, and massive proliferative expansion during pregnancy.
Once lactation ceases, the mammary epithelium undergoes complete remodeling to restore the non-pregnancy state.
Owing to the presence of stem cells, which have the capacity for both self-renewal and differentiation,
this cycle of expansion and regression can continue to repeat itself throughout the reproductive
lifespan of an organism.
The same molecular mechanisms that control normal mammary gland development and function can result in aberrant growth and cancer formation when they are disrupted. As a result, one out of every eight women will develop breast cancer during her lifetime. Moreover, tumor cells often appear to hijack self-renewal mechanisms to drive unlimited cell expansion. Therefore, it is crucial that we understand, and learn to manipulate, the biological signals that control the behavior of the different mammary cell lineages.
We hypothesize that developmental signaling pathways, such as the Wnt pathway, are targets for therapeutic intervention in breast cancer, due to their role in regulating mammary (stem) cell proliferation and differentiation. Our lab uses a variety of experimental approaches, ranging from CRISPR/Cas9 (epi)genome editing in 2D cell culture to primary 3D organoid cultures and in vivo models to study how Wnt proteins control cell fate decisions in complex mammalian tissues.
Historically, mammary gland stem cells are studied in transplantation experiments. However, recent work (including our own) revealed discrepancies between the regenerative potential tested in those assays and the normal developmental potential of the same cell population in situ. Therefore, we use lineage tracing technology to study how Wnt-responsive stem cells contribute to turnover of the mammary gland epithelium in both young and old organisms. We also aim to identify and control the mammary stem cell niche, such that we can ultimately control stem cell behavior at will.
Various aspects of mammary gland development can be modelled in
three-dimensional primary organoid cultures. This allows more advanced experimental
manipulation and detailed imaging by confocal microscopy.
We are using this system to track the behavior of Wnt-responsive stem cells during
tissue morphogenesis and malignant transformation.
Wnt signaling mechanisms
Wnt signaling is crucial for mammary gland development and function, but aberrant Wnt signaling can promote tumor formation. Our goal is to understand how the complex Wnt signaling network controls cell proliferation and cell fate decisions in the mammary gland, not only during normal development and homeostasis, but also in breast cancer. To this end, we are studying how changes in the level of Wnt signaling affect growth and differentiation of the mammary epithelium. In addition, we study the interplay between the Wnt-pathway and other oncogenic lesions.
The Wnt pathway has a high genetic complexity, with the mammalian genome encoding 19 Wnts (ligands) and 10 Frizzleds (receptors). In addition, some Wnt proteins can signal through alternative receptors, such as the receptor tyrosine kinase Ror2. While so-called 'canonical' Wnt signaling (i.e. the activation of beta-catenin/TCF signaling) is quite well understood, many of the alternative, beta-catenin independent responses remain ill defined. Yet the importance of these alternative responses during embryonic development is well established and accumulating evidence suggests that switching between these different branches of the Wnt pathway may play a role in tumor progression.
One particularly intriguing Wnt protein is Wnt5a. Although it can activate signaling through beta-catenin (the so called 'canonical' Wnt-signaling response), it usually activates one of the multiple 'alternative' Wnt-signaling responses. We aim to dissect the signaling activities of Wnt5a at the molecular level. Moreover, we try to understand how Wnt5a signaling controls cell behavior in both healthy and diseased tissues.
Because Wnt signaling is characterized by complex and dynamic intracellular signaling events, we have extended our experimental pipeline with functional imaging studies to gain insight into the spatiotemporal dynamics of the pathway. To this end, we combine novel DNA technologies, such as CRISPR/Cas9 genome editing, with advanced microscopy (a collaboration with dr. Mark Hink).