Ly6a

Ly6A, also known as stem cell antigen-1 (SCA-1), is a cell-surface protein in mice encoded by the Ly6a gene. It belongs to the Ly6/PLAUR domain-containing protein family, a group of small glycosylphosphatidylinositol (GPI)-anchored proteins characterized by a LU-domain and cysteine-rich motifs. The mature protein is attached to the outer leaflet of the plasma membrane via a GPI anchor.

Expression of Ly6A is broad and dynamic. It is widely used as a marker for hematopoietic stem and progenitor cells in adult bone marrow and is expressed on various immune cell subsets, including activated T and B cells, natural killer cells, and dendritic cells, as well as on some endothelial and neural cells. Its expression is influenced by developmental stage and inflammatory signals; interferons and other cytokines can upregulate Ly6A in certain contexts.

Functionally, Ly6A serves primarily as a marker for isolating stem and progenitor populations in mice, frequently used in flow cytometry in combination with other lineage markers. The protein is thought to participate in cell adhesion and signaling, potentially affecting interactions with the extracellular matrix and chemokine receptors, though its precise signaling roles are not fully defined. In addition to its role in stem cell biology, Ly6A expression is associated with immune activation and trafficking in various models.

Humans lack a direct, widely used ortholog of mouse Ly6A. The human LY6 gene family includes several related members (for example LY6E, LY6D, LY6K) that encode similar GPI-anchored proteins involved in immune responses, but they do not function as an exact substitute for Ly6A/SCA-1 as a stem cell marker in humans.