Assertion: epithelium's cell | /r/CapableOf | sprout down into mesenchymal layer
Facets:
Source sentences:
text: This locally secreted factor gives rise to a series of outside-in and inside-out positive feedback between these two types of cells, so that mammary bud epithelial cells can proliferate and sprout down into the mesenchymal layer until they reach the fat pad to begin the first round of branching.