The extracellular matrix gene Frem1 is essential for the normal adhesion of the embryonic epidermis

Area of Science:

• Developmental Biology
• Genetics
• Dermatology

Background:

• Fraser syndrome is a rare genetic disorder with features including cryptophthalmos, syndactyly, and renal defects.
• Mouse blebbing mutants share phenotypic overlap with Fraser syndrome, suggesting their utility as disease models.
• Previous studies identified mutations in Fras1 as a cause for Fraser syndrome and blebbed mice.

Purpose of the Study:

• To identify novel genetic causes of Fraser syndrome and related developmental abnormalities.
• To investigate the function of the Fras1-related extracellular matrix gene 1 (Frem1) in embryonic development.
• To elucidate the role of Frem1 in epidermal adhesion and basement membrane integrity.

Main Methods:

• Genetic analysis to identify mutations in the Frem1 gene in affected mice and patients.
• In utero blistering assays to assess epidermal adhesion.
• Analysis of basement membrane component deposition (collagen VI, Fras1).
• Expression analysis of Frem1 during embryonic development.

Main Results:

• Mutations in Frem1 were identified in both classic head blebs mouse mutants and a new N-ethyl-N-nitrosourea-induced allele.
• Frem1 inactivation leads to in utero epidermal blistering below the basement membrane's lamina densa and renal agenesis.
• Frem1 is expressed in areas of epithelial/mesenchymal interaction and epidermal remodeling.
• Frem1 functions independently of Fras1 and Grip1 in mediating dermal-basement membrane adhesion.
• Collagen VI and Fras1 deposition remain normal in Frem1 mutants, indicating an independent role.

Conclusions:

• Frem1 is a crucial gene involved in Fraser syndrome pathogenesis.
• Frem1 acts as a dermal mediator essential for epidermal adhesion during embryonic development.
• Frem1 plays an independent role in epidermal differentiation and basement membrane integrity, distinct from Fras1 and Grip1 pathways.