Essential requirement for nicastrin in marginal zone and B-1 B cell development

Area of Science:

• Immunology
• Molecular Biology
• Genetics

Background:

• Gamma-secretase is an intramembrane protease complex involved in cleaving amyloid precursor protein and Notch.
• Impaired gamma-secretase function is linked to Alzheimer's disease and familial acne inversa.
• Adaptive immunity defects can arise from genetic mutations.

Purpose of the Study:

• To identify genetic mutations causing defects in adaptive immunity, fur pigmentation, and antibody responses in mice.
• To investigate the role of nicastrin (NCSTN) in the gamma-secretase complex and its impact on B cell development and immune function.

Main Methods:

• Forward genetic screen using N-ethyl-N-nitrosourea-induced mutations in mice.
• Identification and characterization of a missense mutation in the Ncstn gene.
• Analysis of B cell development, antibody responses, fur pigmentation, and intestinal homeostasis in mutant mice.

Main Results:

• A missense mutation in Ncstn severely limits NCSTN glycosylation and impairs gamma-secretase complex integrity and Notch cleavage.
• The Ncstn mutation affects B cell development, specifically transitional-marginal zone precursors and peritoneal B-1 B cells.
• The mutation leads to diminished T cell-independent antibody responses, fur hypopigmentation, and altered intestinal homeostasis.

Conclusions:

• Nicastrin (NCSTN) is essential for proper gamma-secretase function, B cell development, and T cell-independent antibody responses.
• The identified Ncstn allele highlights NCSTN's critical role in specific B cell populations and immune homeostasis.
• This research provides insights into the molecular mechanisms underlying immune deficiencies and pigmentation defects.