Laminin N-terminus α31 expression during development is lethal and causes widespread tissue-specific defects in a transgenic mouse model

Laminins are essential components of all basement membranes where they regulate an extensive array of tissue functions. Alternative splicing from the laminin α3 gene produces a non-laminin but netrin-like protein, Laminin N terminus α31 (LaNt α31). LaNt α31 is widely expressed in intact tissue and is upregulated in epithelial cancers and during wound healing. In vitro functional studies have shown that LaNt α31 can influence numerous aspects of epithelial cell behaviour via modifying matrix organisation, suggesting a new model of laminin auto-regulation. However, the function of this protein has not been established beyond the epithelium and it has never been studied in vivo. Here, a mouse transgenic line was generated using the ubiquitin C promoter to drive inducible expression of LaNt α31. When expression was induced at embryonic day 15.5, LaNt α31 transgenic animals were not viable at birth, exhibiting localised regions of erythema. Numerous striking defects were apparent histologically, including extra-vascular erythrocytes in multiple tissues, kidney epithelial detachment, tubular dilation, interstitial bleeding, and thickening of tubule basement membranes, disruption of the epidermal basal cell layer and of the hair follicle outer root sheath, and ~50% reduction of cell numbers in the liver associated with depletion of hematopoietic erythrocytic foci. These findings demonstrate that LaNt α31 can influence tissue morphogenesis during development. More broadly, these data provide the first in vivo evidence to support an emerging model of laminin self-regulation and provide a valuable model for onward investigation into this important area. Summary Statement Expression during development of Laminin N-terminus α31, a netrin-like laminin splice isoform, caused defects indicating basement membrane disruption in multiple tissues; providing the first in vivo evidence for laminin self-regulation.