Endogenous ecotropic murine leukemia pro- viruses that were not present in the parental stock are ac- quired by the progeny of some SWR/J x RF/J hybrid females. We have made a stock of an ecotropic murine leukemia virus produced by such a hybrid female and inocu- lated newborn SWR/J females with it. We show that upon crossing of the inoculated females to SWR/J males, some of their progeny acquire ecotropic proviruses. Although most of these proviruses appear to be distributed in somatic tissues in a mosaic way, some are transmitted through the germ line. Thus an exogenous infection is able to mimic the phenomenon observed in SWR/J x RF/J hybrid mice. Available evidence suggests that this infection occurs during oogenesis in the recipient female. Our results document the conversion of an exogenous infectious ecotropic murine leukemia virus to an endogenous provirus without any manipulation of either eggs or embryos. virus acquisition in CBA/CaJ x RF/J as compared to SWR/J x RF/J hybrids (6) and also by the fact that ecotropic MuLV RNA is found in the ovary of SWR/J x RF/J hybrids, but not in RF/J females (7). In this paper we show that newborn SWR/J females can be infected with ecotropic MuLV particles originating from SWR/J x RF/J hybrids. The data presented show that such females yield progeny with ecotropic MuLV insertions at a rate compara- ble with SWR/J x RF/J hybrids. We document the trans- mission of some of these proviruses through the germ line. Exogenous infection is thus shown to mimic the phenome- non observed in SWR/J x RF/J hybrids.

The zebrafish Sox-19 belongs to the Sry subfamily of HMG (Hight Mobility Group) box genes and is closely related to the Sox sub-group B, comprising the mouse Sox-1, Sox-2 and Sox-3 genes, with respect to both HMG box homology (95.3%) and neural expression during embryogenesis. Analysis of Sox-19 expression during embryogenesis by whole-mount in-situ hybridization revealed interesting features. In early gastrula embryos, Sox-19 transcripts are detected within a circular area in the region of the presomptive central nervous system (CNS) and appears to be the earliest molecular marker of the CNS in vertebrates. In the developing brain, ZfSox-19 mRNA is distributed in the ventral region of the diencephalon, midbrain and hindbrain whereas the expression is excluded from the telencephalon. In spite of the ventral localisation of its mRNA, the expression of this ZfSox-19 gene is completely normal in cyclops embryos which implies that ZfSox-19 expression is independent of the presence of the floor plate.

The zygotic expression of the eve1 gene is restricted to the ventral and lateral cells of the marginal zone. At later stages, the mRNAs are localized in the most posterior part of the extending tail tip. An eve1 clone (pcZf14), containing a poly-A tail, has been isolated. In order to address eve1 gene function, pcZf14 transcript injections into zebrafish embryos have been performed. The injection into uncleaved eggs of a synthetic eve1 mRNA (12 pg), which encodes a protein of approximately 28 kd, produces embryos with anterior-posterior (A-P) axis defects and the formation of additional axial structures. The first category of 24 h phenotypes (87%) mainly displays a gradual decrease in anterior structures. This is comparable to previous phenotypes observed following Xhox3 messenger injection either in Xenopus or in zebrafish that have been classified according to the index of axis deficiency (zf-IAD). These phenotypes result in anomalies of the development of the neural keel, from microphthalmia to acephaly. The second category (13%) corresponds to the phenotypes described above together with truncal or caudal supernumerary structures. Additional truncal structures are the most prominent of these duplicated phenotypes, displaying a "zipper" shape of axial structures including neural keels and notochords. Caudal duplication presents no evident axis supernumerary structures. The observation of these phenotypes suggests an important role for the eve1 gene in mesodermal cell specification and in the development of the posterior region, and more particularly of the most posterior tail tip where endogenous eve1 messengers are found.

A retroviral vector in which the gag and pol genes have been replaced by the NLS-lacZ reporter gene was derived from a cloned AKV-like virus. A complementing cell line expressing the gag and pol retroviral genes was constructed. The retroviral vector was demonstrated to replicate in the complementing cells. Since transfection is known to generate deletion variants of the introduced plasmid, we have examined whether it can give rise to viral forms with a replicating advantage over the initial vector. After transfection in complementing cells the spread of the vector was followed by X-gal staining. The fraction of stained cells increased for the first 10 days following transfection and was then stabilized to about 20% stained cells, thus defining two cell types; one with LacZ+ phenotype and one with LacZ- phenotype. Molecular analysis showed that the latter contains a deleted form of the virus preventing cell infection by the vector presumably through a mechanism of interference involving the viral env gene. Thus, interference results in the efficient block of vector expansion.

The widespread expression of the Xenopus homeobox gene Xhox3 in zebrafish was performed by microinjection of synthetic Xhox3 mRNA into uncleaved fertilized eggs and resulted in embryos displaying varying degrees of anterior-posterior (A-P) axis disruption. The phenotype observed was dose-dependent and showed anomalies, mainly in neural keel development, from microphthalmia to acephaly. Injection of 5 pg to 10 pg of mRNA caused a range of phenotypes in prim 5 stage embryos from normal to acephalic. Anomalies have been categorized according to an index of axis deficiency (Zf-IAD). We further characterized the axis disturbance by analyzing the expression of two genes implicated in axis formation: engrailed (eng) and brachyury (ntl). eng could not be detected in the muscle pioneer cells of embryos injected with Xhox3. The pattern distribution of brachyury (Ntl) protein is abnormal in Xhox3 injected embryos. Evidence for the conservation of the NH2 terminal region of the Xhox3 protein in frogs and fish is provided by the detection of a nuclear Xhox3-like protein in 24 h zebrafish embryos located in posterior mesoderm tissue. Previous results in Xenopus embryo research and the data presented here support the conservation of an A-P patterning mechanism involving the Xhox3 gene.

We have identified and characterized zebrafish eve1, a novel member of the Drosophila even-skipped (eve) gene family. eve1 RNAs are expressed initially in late blastulae with a peak during the gastrula stage, at which time expression is confined to ventral and lateral cells of the marginal zone of the zebrafish embryo. Later, eve1 transcripts are located in the most posterior part of the extending tail tip. We show that LiCl, known to dorsalize Xenopus embryos, has the same effect in zebrafish, resulting in embryos with exaggerated dorsoanterior structures. In LiCl-treated embryos, eve1 transcripts are completely absent. eve1 is therefore a marker of ventral and posterior cells.In the light of its ventroposterior expression domain, the localization of eve1 transcripts was analysed in spadetail (spt) and no tail (ntl), two mutants with abnormal caudal development. In spt(b140) homozygous mutants, there is an accumulation of cells in the tail region, resulting from inadequate migratory behaviour of precursors to the trunk somites. These cells, in their abnormal environment, express eve1, emphasizing the correlation between ventroposterior position and eve1 expression. In homozygous mutant embryos for the gene ntl (the homologue of mouse Brachyury, originally called Zf-T), posterior structures are missing (M. E. Halpern, C. B. Kimmel, R. K. Ho and C. Walker, 1993; Cell In press). While mutant and wild-type embryos do not differ-in their eve1 transcript distribution during gastrulation, eve1 expression is absent in the caudal region of mutant ntl embryos during early somitogenesis, indicating a requirement for ntl in the maintenance of eve1 expression during tail extension.Our findings suggest that eve1 expression is correlated with a ventral and posterior cell fate, and provide first insights into its regulation.

We have identified and characterized the zebrafish eve1 homeo box gene, a member of the Drosophila even-skipped (eve) gene family. eve1 is expressed in the most posterior part of the tail bud during somitogenesis. During gastrulation, transcripts are confined to ventral and lateral cells of the marginal zone of the embryo. We show that LiCl, known to dorsalize Xenopus embryos, has the same effect in zebrafish embryos. In LiCl-treated embryos, eve1 transcripts are completely absent, suggesting that eve1 marks the ventral specification of mesoderm in zebrafish gastrulae.

We have isolated a molecular clone of an ecotropic murine leukemia virus from the ovaries of an SWR/J × RF/J hybrid female. The molecularly cloned virus, named pSR3, was demonstrated to induce virus production upon transfection into SWR/J immortalized fibroblasts and to promote germ line integration of proviruses in a fraction of the offspring germline when inoculated to neonate SWR/J females. Sequence analysis reveals that pSR3 is closely related to p623, a plasmid derived from Emv-11 (also referred to as AKV-1). Alignment of the pSR3 sequence with the partial nucleotide sequence of Emv-11 (an endogenous virus carried by BALB/c and C3H/He mice) together with p623 then allows a comparison between three vital sequences. Analysis of these data gives (a) an estimation of the natural divergence rate of MuLV genomes in the course of viral replication (1-5 × 10-5 mutations per cycle and per nucleotide) and (b) molecular evidence for a recent origin through germ line infection of endogenous loci. From additional clues, Emv -11 appears to be the probable ancestor of at least some of these loci.

This paper deals with the first identification of a caudal cDNA containing a homeobox of the Drosophila caudal family in the zebrafish. A cDNA library from late gastrula stage embryos was constructed and screened with a mouse Cdx 1 homeobox probe. A 1.6 kb cDNA clone containing a homeobox related to other caudal homeoboxes was isolated and called cdx[Zf-cad1]. Analysis of the predicted 301 amino acid translation product reveals additional regions of homology outside the homeodomain with other members of the caudal family. Particularly, the cdx[Zf-cad1] putative protein shares a conserved N-terminal region with its chicken homolog CHox-cad. Transcripts are first detected just before the onset of gastrulation. At the beginning of gastrulation, a single 1.8 kb cdx[Zf-cad1] transcript is located near the blastoderm margin with a high level of expression restricted to the epiblast. At this stage, the hypoblast is clearly negative. At the end of gastrulation, cdx[Zf-cad1] is widely expressed in vegetal (i.e. prospective posterior) epiblast and hypoblast, with a somewhat weaker expression in the dorsal hypoblast. During somitogenesis, cdx[Zf-cad1] exhibits a posterior regionalization in the neurectoderm. In contrast, no expression is detected in the mesoderm of 22 h embryos (late somitogenesis). Posterior endoderm is also positive at this stage. cdx[Zf-cad1] transcripts cease to be detected about 48 h after fertilization. They are undetectable in the adult, particularly in female gonads. The pattern of cdx[Zf-cad1] expression during and after gastrulation is consistent with its possible involvement in the regionalization of the embryo at these stages.(ABSTRACT TRUNCATED AT 250 WORDS)

Hepatic nuclear factor 1 (HNF1) is a highly diverged homeoprotein that is crucial for transcription of many liver-specific genes including albumin. In particular, a minimal promoter, consisting of an HNF1-binding-site and a TATA box, is highly active only in hepatoma cell lines. The expression of the HNF1 and albumin genes has been examined in mouse embryos by in situ hybridization. At 10.5 days of gestation, the HNF1 mRNA was detected in both the hepatic primordia and visceral endoderm of the yolk sac whereas the albumin transcript was present only in the nascent liver. At later stages of development, HNF1 was detected in liver, in the epithelial cells of most of the digestive tract and in the cortex of the kidney, whereas albumin was again found only in the liver. The presence of HNF1 protein in adult kidney was demonstrated by immunodetection in gel-retardation assays and western blot analysis. These experiments show that, even though the HNF1 homeo-protein is essential for expression of many liver-specific genes, it cannot, by itself, force high expression levels of these genes, in non-hepatic tissues.

BioEssaysVolume 13, Issue 7 p. 351-356 Feature Mitotic recombination in mammals Jean-Jacques Panthier, Jean-Jacques Panthier Unité de Génétique Cellulaire, Institut Pasteur, 25 rue du Docteur Roux, Paris Cedex 15, 75724, FranceSearch for more papers by this authorHubert Condamine, Hubert Condamine Unité de Génétique Cellulaire, Institut Pasteur, 25 rue du Docteur Roux, Paris Cedex 15, 75724, FranceSearch for more papers by this author Jean-Jacques Panthier, Jean-Jacques Panthier Unité de Génétique Cellulaire, Institut Pasteur, 25 rue du Docteur Roux, Paris Cedex 15, 75724, FranceSearch for more papers by this authorHubert Condamine, Hubert Condamine Unité de Génétique Cellulaire, Institut Pasteur, 25 rue du Docteur Roux, Paris Cedex 15, 75724, FranceSearch for more papers by this author First published: July 1991 https://doi.org/10.1002/bies.950130709Citations: 6AboutPDF ToolsRequest permissionExport citationAdd to favoritesTrack citation ShareShare Give accessShare full text accessShare full-text accessPlease review our Terms and Conditions of Use and check box below to share full-text version of article.I have read and accept the Wiley Online Library Terms and Conditions of UseShareable LinkUse the link below to share a full-text version of this article with your friends and colleagues. Learn more.Copy URL Share a linkShare onFacebookTwitterLinked InRedditWechat Citing Literature Volume13, Issue7July 1991Pages 351-356 RelatedInformation