H2afy deletion causes female-specific steatosis. Pathological analysis of the livers from (b, d) H2afy-targeted and (a, c) littermate control mice stained with (a, b) hematoxylin and eosin and (c, d) oil-red O. (b) Microscopic examination of the livers revealed that H2afy-/- animals exhibited macrovesicular steatosis mainly in the periportal areas. Strikingly, hepatic steatosis was observed only in H2afy-/- females. (d) Hepatic steatosis was due to the accumulation of neutral fat in liver, as documented by the positive oil red O staining. The long arrow indicates the portal tract and the short arrow the centrilobular vein.