We examined histochemically and immunohistochemically the distribution of B- and Z-DNA in the epithelium and terminally differentiating dog lens fiber cells. On the basis of anti-DNA antibody reactivity, qualitative and quantitative data on B- and Z-DNA in cells were determined. Anti-B-DNA immunoreactivity gradually declined throughout nucleated fibers, with a precipitous decrease at approximately 90 microns. Anti-Z-DNA antibody binding decreased with a sudden loss of immunoreactivity at approximately 90 microns. The pattern of anti-B- and Z-DNA staining correlates with the loss of alpha-crystallin immunoreactivity, the major lens crystallin, and decreased eosin staining of proteins. Germinative zone cell nuclei showed the highest DNA probe binding values, followed by the superficial fibers, central zone, middle fibers, and deep fibers. The presence of single-stranded (ss)DNA in deeper fibers was detected by anti-ss-DNA antibodies. This is indicative of DNA degradation. These observations suggest that a dramatic reorganization of lens fiber cells' supramolecular order occurs at approximately 90 microns, the phase transition zone.

Xeroderma pigmentosum is a rare, recessively transmitted disease associated with increased sensitivity to ultraviolet radiation in wavelengths found in sunlight, development of cancers in sun-exposed areas of the body in much larger numbers and much earlier in life than in normal individuals, and in some patients, neurologic deficiencies unrelated to sun exposure. Extensive cellular, biochemical, and molecular genetic studies in numerous laboratories have revealed that cells derived from patients with this disease have defective repair of ultraviolet-light-induced damage in cellular DNA, and that extensive genetic heterogeneity and numerous distinct genes are involved in the genetics of this disease and the etiopathogenesis of its associated changes. A number of these genes and gene products are now being, or have been, cloned, and their gene products characterized.

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Bovine zeta-crystallin has the ability to bind with different DNAs. Initially, this protein was named regulatory factor 36 (Kang et al., 1985), but it has been shown to be an ocular lens zeta-crystallin (Jörnvall et al., 1993), which is considered an enzyme-crystallin (Rodakanaki et al., 1989). The enzyme-linked immunosorbent assay (ELISA) was used to quantitate the binding of bovine zeta-crystallin to purified high molecular weight double-stranded (ds-) and single-stranded (ss-) DNA (bovine and synthetic DNA). ELISA quantitation was achieved by the addition of anti-zeta-crystallin antibodies to the DNA-zeta-crystallin complex, using a novel immunochemical avidin-biotin method. Zeta-crystallin shows much greater binding intensity for ss-DNA and for ds-Z-DNA than for ds-B-DNA. It also reacts slightly more with ds-Z-DNA than ss-DNA. Therefore, we speculate that zeta-crystallin may act as a transcriptional enhancer (outer lens cortex), possibly binding to Z-DNA regulatory elements within lens crystallin genes. It may also act to protect DNA from endogenous DNase activity and as a DNA unwinding (destabilizing) protein also involved with transcription, occurring in normal adult bovine lens nucleated secondary fiber cells.

The portal vein wall typically is hyperechoic over a wide range of beam-vessel angles, whereas the hepatic vein wall is hyperechoic only when the inci· dent beam and the vessel are perpendicular. This has been attributed to marked discrepancies in mural thickness, collagen content, or perivascular fat between portal and hepatic veins. We evaluated histologically the walls of portal and hepatic veins using three cadaveric livers. For vessels with lumi· nal diameter above 2 to 3 mm, hepatic vein and portal vein wall thicknesses were similar such that portal vein walls were not more than 50% thicker than those of hepatic veins of comparable size. Hepatic vein walls were mostly composed of parallel, tightly packed collagen fibers. In contrast, portal vein walls were composed of loosely arrayed, non parallel connective tissue fibers which were separated by multiple intervening spaces and only a minority of which were collagenous. Perivascular fat was not identified adjacent to intrahepatic vessels beyond the liver hilus. The marked differences in echogenicity between portal vein and hepatic vein walls typically observed at ultrasonography thus cannot be attributed to differences in mural thickness, collagen content, or perivascular fat between these vessels. Rather, the distinct composition of the hepatic vein wall renders it a specular reflector, which is hyperechoic only when the angle between the ultrasound beam and the vessel wall is dose to 90 degrees, whereas the composition of the portal vein wall enables it to appear hyperechoic at a wide range of beam-vessel angles. KEY WORDS: Liver, ultrasonography; Abdomen, ultrasonography; Hepatic vein; Portal vein. I t has long been known that echoes reflected from HV walls typically are less bright than those reflected by PV walls. Chafetz and Filly noted that HV walls were hyperechoic when HVs were aligned perpendicular to the ultrasonographic beam, in contrast to PV walls, which were hyperechoic over a wide range of beam-vessel angles.l They suggested that this phenomenon was due to more abundant connective tissue in PV walls than in HV walls,l an extrapolation based on the wellknown marked discrepancy in thickness between HV and PV walls at the level of the microscopic hepatic lobule.z They also suggested that differences between PVs and HVs in the quantity of perivascular fat might contribute to observed differences in echogenicity.l The imaging literature has supported the idea that the discrepancy between PV and HV 0 1997 by the American Institute of Ultrasound in Medicine • J Ultrasound Med 16:807-810, 1997 • 0278-4297/ 97/ $3.50