The aim of this Master’s thesis was to investigate the role of LMα5 in MG development, as it has not been researched before. MG development is an intricate process involving an interplay of several systemic and local factors.
The investigations in this thesis were divided into in vitro and in vivo methods. The in vitro methods involved analysis of growth rates and structures of organoids grown from isolated MMECs, and the in vivo methods explored the development and structure of the mammary tree in isolated MGs.
According to the findings of this thesis, LMα5 is a key player in MG development, as witnessed by the in vitro branching assay and in vivo experiments. Branching morphogenesis is stunted in LAMA5 knockout cells and mice. Organoids grown from LAMA5 deficient cells form fewer branches than their wild type counterparts. In MGs isolated from mice lacking LMα5, both epithelial length and number of TEB structures, key points for branching morphogenesis, are reduced. On closer inspection of epithelial structure, disorganized luminal assembly can be observed, with detached aggregates of cells in the ductal lumen. This can be a sign of loss of luminal epithelial cell contact with the BM, as luminal cells normally are in charge of LMα5 deposition into the BM. Loss of BM contact can also result in disturbed apico-basal polarity, an event witnessed in other LMα5 deficient tissues researched before. This deduction is fortified by related studies where loss of β1 integrin, a mediator of laminin signaling, has been shown to result in defective cellular polarity. Together, these findings indicate a disturbance in normal MG development and tissue remodeling in LMα5 deficient MGs.
The experiments performed for this thesis lay a groundwork for further studies on the significance of LMα5, and other understudied laminins, on MG development. As LMα5 has been shown to enforce luminal expression of epithelial cells, it would be interesting to explore its effects throughout MG development, beginning from MaSC lineage re-striction in the embryo. Future studies can also concentrate on more detailed investigations on the mechanisms behind the phenomena displayed in pubertal and pregnant LMα5 knockout glands.
In addition to significance in developmental biology, the presented findings can have a consideration in future MG tissue engineering applications. In the tissue engineering
triad, scaffolds are often described as the supportive framework on which tissues and organs can be built. They provide cues for cellular proliferation and differentiation. ECMs and BMs are nature’s own scaffolds, working in concert with cells to build functional units.
In MG, this concert is in discord when LMα5 is removed.
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