E3 ligase Rbx1 orchestrates thymus development and fate determination of alpha/belta & gamma/delta T cells

T lymphocytes comprise of alpha/belta and gamma/delta T cells, which mature and differentiate from the same progenitor cells in the thymus. Cullin-RING ligases (CRLs), the largest family of ubiquitin ligases, requires neddylation on the scaffold protein Cullins for their ligase activity. The role of neddylation-CRL system in thymus development and the fate determination of alpha/belta-gamma/delta T cells remains elusive. Here, we generated conditional knockout mouse models with thymus deletion of neddylation conjugating enzymes Ube2m or Ube2f, or dual neddylation and CRL E3s Rbx1 or Sag, individually. We found that only Rbx1, not Ube2m/Ube2f nor Sag, plays a significant role in thymus development and fate determination of alpha/belta-gamma/delta T cells. Specifically, Rbx1 loss causes shrinkage of the thymus, delayed T cell development, increased gamma/delta T cells in the thymus with increased the ratio of immature Grza+ gamma/delta T cells and decreased the ratio of the proliferative subpopulation. Some of these phenotypes were moderately rescued by simultaneous Bim deletion. Mechanistically, Rbx1 loss alters the Akt, NF-kB, and metabolic pathways in progenitor of gamma/delta T cells DN3a cells. Finally, Rbx1 loss altered the gamma/delta T1/T17 cell population in the thymus, suggesting that Rbx1 controls the fate of gamma/delta T cells.