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Chicken erythrocyte histones 2A, 2B, and 3 can be resolved into nonallelic primary structure variants by polyacrylamide gel electrophoresis in the presence of Triton X-100. These variants were isolated and characterized by analysis of their tryptic and thermolytic peptides. The major variants of chicken H2A and H2B differ from the analogous component of calf thymus by a small number of conservative amino acid substitutions in the basic terminal regions, which interact with DNA. This moderate rate of allelic evolution of the slightly lysine-rich histones contrasts with the complete conservatism found in the arginine-rich histones. Chicken H4 and both chicken H3 variants are identical with their corresponding components in mammals. The amino acid substitutions distinguishing histone variants are located within the highly conserved hydrophobic regions, which are involved in histone--histone interactions.

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The formation of somites, reiterated structures that will give rise to vertebrae and muscles, is thought to be dependent upon a molecular oscillator that may involve the Notch pathway. hairy/Enhancer of split related [E(spl)]-related (her or hes) genes, potential targets of Notch signaling, have been implicated as an output of the molecular oscillator. We have isolated a zebrafish deficiency, b567, that deletes two linked her genes, her1 and her7. Homozygous b567 mutants have defective somites along the entire embryonic axis. Injection of a combination of her1 and her7 (her1+7) morpholino modified antisense oligonucleotides (MOs) phenocopies the b567 mutant somitic phenotype, indicating that her1 and her7 are necessary for normal somite formation and that defective somitogenesis in b567 mutant embryos is due to deletion of her1 and her7. Analysis at the cellular level indicates that somites in her1+7-deficient embryos are enlarged in the anterior-posterior dimension. Weak somite boundaries are often found within these enlarged somites which are delineated by stronger, but imperfect, boundaries. In addition, the anterior-posterior polarity of these enlarged somites is disorganized. Analysis of her1 MO-injected embryos and her7 MO-injected embryos indicates that although these genes have partially redundant functions in most of the trunk region, her1 is necessary for proper formation of the anteriormost somites and her7 is necessary for proper formation of somites posterior to somite 11. By following somite development over time, we demonstrate that her genes are necessary for the formation of alternating strong somite boundaries. Thus, even though two potential downstream components of Notch signaling are lacking in her1+7-deficient embryos, somite boundaries form, but do so with a one and a half to two segment periodicity.

We tested the hypothesis that duck hepatitis B virus (DHBV) is a naturally occurring congenital infection of Pekin duck embryos. Of 219 embryos, 5-25 days after being laid, sera from 30 were found to be positive for endogenous DNA polymerase activity characteristic of hepatitis B-related viruses. The presence of the duck virus was confirmed by hybridization with cloned DHBV DNA. Viral DNA was also found in the livers of embryos incubated for 12 or 18 days. Electrophoretically different forms of DHBV DNA were identified in liver extracts that were not present in serum. These additional liver forms probably represent viral replication intermediates. These observations suggest that the vertical route is a major pathway of DHBV transmission and that viral replication may be initiated by the 12th day of embryonic life.Infection with human hepatitis B virus (HBV) is a worldwide health problem. The majority of HBV infections are acute and are followed by complete recovery with the development of antibody to the surface antigen of the virus (anti-HBs). In areas of the world where the virus is endemic (Southeast Asia, China, and Africa), most of the members of the population have been infected and a significant proportion (3-20%) are chronically infected. Persistent infection with HBV is associated with chronic liver disease and primary hepatocellular carcinoma (PHC) (1-3).Study of the role of HBV in liver carcinogenesis has been hampered by the limited host range of HBV (man and chimpanzees) and the lack of an in vitro system for viral propagation. Recently, it has been shown that HBV belongs to a family of hepatitis B viruses (4) that includes woodchuck hepatitis virus (WHV) (5), ground squirrel hepatitis virus (6), and Pekin duck HBV (DHBV) (7). Since persistent infection ofwoodchucks with woodchuck hepatitis virus leads to the development of PHC (5) Methods. Cells and nuclei. Embryos from eggs incubated 5 days were explanted by trimming around the sinus terminalis and blood was isolated from these embryos by cannulation of the vitelline vessels. Blood was obtained from older embryos by cardiac puncture. Twelve-and 18-day-incubated duck embryos were dissected free of extra-embryonic membranes and rinsed in chicken Ringer's solution to remove adhering yolk; the livers were removed and frozen at -70°C. Nuclei were isolated from the frozen livers as described (13). The supernatant (25 ml) from the first homogenization and centrifugation in 10 mM K/Tris maleate, pH 7.4/5 mM CaC12/25 mM glycine (the postnuclear supernatant) and the nuclei were saved for DNA extraction and assay of DHBV-specific DNA.Extraction of DNA. The nuclei and postnuclear supernatant were digested with Pronase at 100 ,ug/ml in 0.15 M NaCl/0. 1 M EDTA/0.2% NaDodSO4 for 1 hr at 37°C. Nucleic acids were deproteinized by two extractions with Tris-buffered phenol/ chloroform, pH 8.0, followed by one extraction with chloroform. The aqueous phase was adjusted to 0.2 M NaOAc and the nucleic acids were precipitated with 2.5 vol ofabsolute ethanol. Th...