Critical for B-cell development. Interacts with VPREB1 (By similarity). Interacts with SYNV1/HRD1 (via N-terminus); this interaction leads to increased IGLL1 ubiquitination and degradation in pre-B cells, possibly through a lysosomal, not proteasomal, pathway (PubMed:29907570). In pre-B cells, localizes predominantly to the endoplasmic reticulum. Selectively expressed in pre-B lymphocytes.