Coordinating cell fate specification and morphogenesis in the developing mouse mammary epithelium – BranchFate

How cells coordinate morphogenesis and fate specification is a fundamental question underlying tissue development, homeostasis and regeneration. These two processes have mainly been studied independently. In the embryonic mouse mammary gland, we found that stem cells engage into unipotency during a narrow time window that coincides with the initial morphogenetic events generating the mammary branched tree. This project aims to integrate for the first time the transcriptional signatures defining specific cell states with 4D cell dynamics during branching morphogenesis, in order to decipher the molecular mechanisms underlying cell identity acquisition and its dependency on branching morphogenesis.
By combining a set of interdisciplinary approaches, we will pursue the following three complementary aims:

Aim 1. Define the developmental timing and molecular signatures dictating mammary cell differentiation.
Using a novel lineage tracing technique by genetic barcoding and single cell transcriptomics, we will quantitatively define the proportion of multipotent and unipotent mammary stem cells at the clonal level and combine this information on cell fate potential with the transcriptional landscapes that determine mammary cell identity and potency.

Aim 2. Characterize cell and tissue dynamics driving mammary tubulogenesis.
Using original live-imaging of embryonic mammary explants and advanced cell tracking approaches, we will fully map the cell dynamics associated with mammary bud branching and cell fate specification. By biasing cell fate commitment in mouse mutants, we will then define the molecular mechanisms coupling cell dynamics and lineage specification.

Aim 3. Link subcellular dynamics and cell movements during branching morphogenesis.
Using fluorescent reporters, inhibitors and genetic mutants in mammary explants, we will characterize the dynamics of the cytoskeleton and cell adhesion networks governing individual and collective cell displacements during mammary branching and define how they control cell fate specification and morphogenesis.

We expect that our findings will unveil the molecular circuitries driving mammary branching and linking specific stem cell states to cell dynamics during morphogenesis. Therefore, we will advance our understanding of how organs are formed during development. We also foresee that the results derived from the proposed studies may lead to uncover unexpected regulators of MaSCs differentiation and cell dynamics, which may have a conserved role in other stem cells and tissues. As such, our findings will be relevant not only for mammary gland development, but for the wider fields of stem cell commitment, tissue architecture and organogenesis.