No abstract

The vertebrate inner ear develops from an ectodermal placode adjacent to rhombomeres 4 to 6 of the segmented hindbrain. The placode then transforms into a vesicle and becomes regionalised along its anteroposterior, dorsoventral and mediolateral axes. To investigate the role of hindbrain signals in instructing otic vesicle regionalisation, we analysed ear development in zebrafish mutants for vhnf1, a gene expressed in the caudal hindbrain during otic induction and regionalisation. We show that, in vhnf1 homozygous embryos, the patterning of the otic vesicle is affected along both the anteroposterior and dorsoventral axes. First, anterior gene expression domains are either expanded along the whole anteroposterior axis of the vesicle or duplicated in the posterior region. Second, the dorsal domain is severely reduced, and cell groups normally located ventrally are shifted dorsally, sometimes forming a single dorsal patch along the whole AP extent of the otic vesicle. Third, and probably as a consequence, the size and organization of the sensory and neurogenic epithelia are disturbed. These results demonstrate that, in zebrafish, signals from the hindbrain control the patterning of the otic vesicle, not only along the anteroposterior axis, but also, as in amniotes, along the dorsoventral axis. They suggest that, despite the evolution of inner ear structure and function, some of the mechanisms underlying the regionalisation of the otic vesicle in fish and amniotes have been conserved.

The homeobox-containing gene variant hepatocyte nuclear factor-1 (vHnf1) has recently been shown to be involved in zebrafish caudal hindbrain specification, notably in the activation of MafB and Krox20 expression. We have explored this regulatory network in the chick by in ovo electroporation in the neural tube. We show that misexpression of vHnf1 confers caudal identity to more anterior regions of the hindbrain. Ectopic expression of mvHnf1 leads to ectopic activation of MafB and Krox20, and downregulation of Hoxb1 in rhombomere 4. Unexpectedly, mvhnf1 strongly upregulates Fgf3 expression throughout the hindbrain, in both a cell-autonomous and a non-cell-autonomous manner. Blockade of FGF signaling correlates with a selective loss of MafB and Krox20 expression, without affecting the expression of vHnf1, Fgf3, or Hoxb1. Based on these observations, we propose that in chick, as in zebrafish, vHnf1 acts with FGF to promote caudal hindbrain identity by activating MafB and Krox20 expression. However, our data suggest differences in the vHnf1 downstream cascade in different vertebrates. Developmental Dynamics 234:567-576, 2005.

The features of Hepatitis C virus (HCV) quasispecies within an envelope segment including the hypervariable region 1 were analysed at an early time point post-infection in seven patients that acquired HCV from a single common donor during a nosocomial outbreak. The grouping of patients according to viral load was reflected in the structure of the quasispecies. A higher viral load correlated with the presence of a predominant HCV genome and a corresponding lower quasispecies complexity. The quasispecies complexity itself was not correlated with HCV clearance or persistence. Thus, the relationship between an intrapatient HCV quasispecies and the clinical outcome of an HCV infection is more complex than previously anticipated. INTRODUCTIONHepatitis C virus (HCV) is an enveloped positive-strand RNA virus of the family Flaviviridae. Only about 15-30 % of HCV infections are spontaneously cleared, the remaining result in virus persistence with subsequent development of chronic hepatitis, liver cirrhosis and hepatocellular carcinoma (Alter et al., 1999). Because worldwide over 170 million people are infected carriers, HCV is a major health problem and a key issue in antiviral research.The mechanisms responsible for the high rate of viral persistence are thought to be the result of a complex host-virus interaction early after infection (Racanelli & Rehermann, 2003). However, little is known about these early virus and host determinants because the acute phase of infection is often asymptomatic and thus most diagnoses are made during the chronic stage, i.e. months or years after the events that determined the clinical course of the infection. While HCV induces strong humoral and cellular immune responses, their roles in virus clearance or persistence have not been fully elucidated. Studies in humans and chimpanzees indicate that a robust intrahepatic CD4 + and CD8 + T-cell response during the first weeks after infection is associated with viral clearance (Cooper et al., 1999;Major et al., 2004;Thimme et al., 2002). Also, antibodies may play a role here because an early antibody recognition of the hypervariable region 1 (HVR1) in the envelope E2 protein was correlated with virus clearance (Allander et al., 1997), and infection of chimpanzees could be inhibited by a human hyperimmune serum against HVR1 (Farci et al., 1996). In line with this are studies on the rate of HVR1 evolution that have suggested that the HVR1 region is under immune pressure exerted by neutralizing antibodies (Booth et al., 1998;Kato et al., 1993; Shimizu et al., 1994;Weiner et al., 1992). Nevertheless, by using infectious retroviral pseudotypes, a recent study has shown that neutralizing antibody responses early after infection do not seem to play a role in the resolution of an acute infection (Logvinoff et al., 2004 aspect is that HCV seems to have a wide cell tropism and can infect not only hepatocytes but also cells of the immune system (Bain et al., 2001;Sung et al., 2003). Another important feature is that HCV behaves in infected patients as a c...