CUBN and diabetes mellitus: Figure 1(b) shows that megalin gene expression was similar in control and diabetic kidneys at 10 and 15 weeks after the onset of diabetes. In contrast, after 18 weeks of diabetes, megalin expression increased significantly in the diabetic animals. Megalin and cubilin function as co-receptors involved in the uptake and endocytosis of many small-molecular-weight proteins in the proximal tubule.  Figure 1(c) shows that renal gene expression of the co-receptors megalin and cubilin in DBA/2J kidneys (10–18 weeks) is highly correlated (r = 0.8284; P < .0001).