Eveline Seifert

The homeotic gene fork head encodes a nuclear protein and is expressed in the terminal regions of the Drosophila embryo

The region-specific homeotic gene fork head (fkh) promotes terminal as opposed to segmental development in the Drosophila embryo. We have cloned the fkh region by chromosomal walking. P element-mediated germ-line transformation and sequence comparison of wild-type and mutant alleles identify the fkh gene within the cloned region. fkh is expressed in the early embryo in the two terminal domains that are homeotically transformed in fkh mutant embryos. The nuclear localization of the fkh protein suggests that fkh regulates the transcription of other, subordinate, genes. The fkh gene product, however, does not contain a known protein motif, such as the homeodomain or the zinc fingers, nor is it similar in sequence to any other known protein.

cis-acting control elements for Kruppel expression in the Drosophila embryo.

Krüppel (Kr), a gap gene of Drosophila, shows complex spatial patterns of expression during the different stages of embryogenesis. In order to identify cis‐acting sequences required for normal Kr gene expression, we analysed the expression patterns of fusion gene constructs in transgenic embryos. In these constructs, bacterial lacZ expression was placed under the control of Kr sequences in front of a basal promoter. We identified cis‐acting Kr control units which drive beta‐galactosidase expression in 10 known locations of Kr expression in early and late embryos. More than one cis‐regulatory element drives the expression in the anterior domain at the blastoderm stage, in the nervous system, the midline precursor cells and in the amino‐serosa. In addition, two cis‐acting elements direct the first zygotic expression of Kr in a striped subpattern within the central region of the blastoderm embryo. Both elements respond to alterations in the activities of maternal organizer genes known to be required for Kr expression in establishing the thoracic and anterior abdominal segments in the wild‐type embryo.

Gradients of Krüppel and knirps gene products direct pair-rule gene stripe patterning in the posterior region of the drosophila embryo

Abdominal segmentation of the Drosophila embryo requires the activities of the gap genes Krüppel (Kr), knirps (kni), and tailless (tll). They control the expression of the pair-rule gene hairy (h) by activating or repressing independent cis-acting units that generate individual stripes. Kr activates stripe 5 and represses stripe 6, kni activates stripe 6 and represses stripe 7, and tll activates stripe 7. Kr and kni proteins bind strongly to h control units that generate stripes in areas of low concentration of the respective gap gene products and weakly to those that generate stripes in areas of high gap gene expression. These results indicate that Kr and kni proteins form overlapping concentration gradients that generate the periodic pair-rule expression pattern.

Differential regulation of the two transcripts from the Drosophila gap segmentation gene hunchback.

The Drosophila gap gene hunchback (hb) is required for the establishment of the anterior segment pattern of the embryo, and also for a small region of the posterior segment pattern. The hb gene encodes two transcripts from two promoters which show a differential regulation, although they code for the same protein product. The 3.2‐kb transcript is expressed during oogenesis and forms an anterior‐posterior gradient during the early stages of development. The first zygotic expression of hb during cleavage stages 11‐12 is due to the 2.9‐kb transcript. Its expression is under the control of the anterior pattern organizer gene bicoid (bcd) and it appears to be necessary and sufficient for the anterior segmentation. The 3.2‐kb transcript is expressed again at syncytial blastoderm stage in the anterior yolk nuclei, as well as in an anterior stripe which is posteriorly adjacent to the domain of the 2.9‐kb transcript, and as a posterior stripe. Using hb‐promoter/lacZ fusion gene constructs in combination with germ line transformation, we have delimited a regulatory region for the 2.9‐kb transcript to approximately 300 bp upstream of the site of transcription initiation and show that this region is sufficient to confer the full regulation by bcd.

Gene expression mediated by cis-acting sequences of the Krüppel gene in response to the Drosophila morphogens bicoid and hunchback.

The initial expression of the gap gene Krüppel (Kr) occurs in a precisely bounded central region of the Drosophila blastoderm embryo. According to genetic analysis, the spatial limits of the Kr expression domain are controlled by the morphogenetic activities of the anterior organizer gene bicoid (bcd) and the anterior gap gene hunchback (hb). Using gene fusion analysis, we assayed for cis‐acting sequences of the Kr gene which mediate transcriptional activation and localized gene expression in response to trans‐acting factors. A 730 bp Kr control element drives gene expression in place of the endogenous Kr central domain. This cis‐acting element, Kr730, is composed of bcd and hb responsive sequences. They map into regions of multiple hb and bcd protein in vitro binding sites. A 142 bp core fragment containing one low affinity hb and five medium to strong bcd protein binding sites drives gene expression in a Kr‐like location in the centre of the embryo. Our results show that this fragment represents a target for the redundant activator/repressor system provided by the anterior morphogens bcd and hb.

Properties of mouse leukemia viruses: VIII. The major viral glycoprotein of Friend leukemia virus. Seroimmunological, interfering and hemagglutinating capacities

Abstract The purified major glycoprotein (GP 71 ) of Friend leukemia virus revealed type-specific as well as species-specific and interspecies antigenicities in various types of seroimmunological tests. It was also able to induce the production of neutralizing antibodies, to interfere with murine leukemia viruses from two different serotypes, and to hemagglutinate. Demonstration of hemagglutination became possible after reconstitution of GP 71 to multivalent complexes by suitable species-specific antibody (indirect hemagglutination).

The gooseberry-zipper region of Drosophila: five genes encode different spatially restricted transcripts in the embryo.

Genetic analysis of the Drosophila chromosome region 60 E9‐F1 identified two functions affecting embryonic development; gooseberry (gsb), a segment polarity gene, and zipper (zip), an unclassified gene which affects cuticle formation severely. By contrast, molecular analysis revealed five genes with different temporal and spatial patterns of expression in the embryo. Candidate genes for gsb and zip functions were identified. Two adjacent genes are eventually expressed in regular stripes within the posterior region of each segment. One of them is expressed initially in a pair‐rule mode; the second gene expresses reduced levels of transcripts in a mutant which leaves the transcribed region and the sequences up to the second gene intact. This observation, the patterns of transcripts in the embryo and the genetic data suggest that both genes are involved in gooseberry segmentation function. zip is expressed in neural tissue and not in epidermal anlagen. Embryos lacking zip activity also develop abnormal neural tissue consistent with the argument that the zip cuticle phenotype is a secondary effect. Additional newly identified genes are expressed in specific domains of the embryo, covering mesoderm anlagen and the dorsal region of embryos at blastoderm stage, respectively.

Molecular characterization of spalt, a homeotic gene required for head and tail development in the Drosophila embryo

The isolation, identification and structure of the spalt gene is described. This novel homeotic gene of Drosophila is required for the establishment of the posterior‐most head and the anterior‐most tail segments of the embryo. It encodes a small mRNA of 0.8 kb which is under the control of over 15 kb of upstream sequences as indicated by the phenotype of transformed embryos. The putative spalt protein contains internal repeats and other interesting structural motifs but no homeo box. The spalt transcript accumulates motifs but no homeo box. The spalt transcript accumulates to high levels in the segmental anlagen affected in mutant embryos but is also found in regions of the embryo where no functional requirement has been demonstrated.

Regulatory elements controlling expression of the Drosophila homeotic gene fork head

The region‐specific homeotic gene fork head (fkh) is expressed and required in a variety of tissues of the developing Drosophila embryo. In order to identify the cis regulatory elements directing the complex spatio‐temporal expression pattern of fkh, we have studied the subpatterns directed by defined fragments of fkh genomic DNA. These experiments enabled us to distinguish separate regulatory elements specific for the different expression domains of fkh. In addition, our analysis revealed several unexpected features such as the redundancy of regulatory elements and the overlap of regulatory elements with the transcribed regions of other genes. Moreover, the separation of normally contiguous elements effecting expression in the posterior terminal fkh domain appears to lead to novel expression domains which do not correspond to known developmental units in the embryo.

Axon growth from limb motoneurons in the locust embryo: The effect of target limb removal on the path taken out of the central nervous system

Abstract Removal of the metathoracic limb bud from locust embryos at 25 to 30% of embryogenesis has a specific effect on the outgrowth of axons from a particular group of motoneurons: nerve root 5 is missing in these animals and the neurons which normally send axons out this nerve leave the ganglion by nerve roots 3 and/or 4. The choice of exit pathway made by individual identified axons is variable. When remnants of the metathoracic leg which include traces of the femur are present after the operation, nerve 5 is present and contains a normal complement of motor axons. This suggests that in normal development some factor near the anlage of the coxal-femoral joint specifies the pathway taken by the axons of nerve 5 motoneurons out of the metathoracic ganglion. Two peripheral neurons seen in this region of the limb bud in prekatatrepsis embryos are likely candidates for this role.