Heparan sulfate proteoglycans are essential for FGF receptor signaling during Drosophila embryonic development.

The Drosophila sugarless and sulfateless genes encode enzymes required for the biosynthesis of heparan sulfate glycosaminoglycans. Biochemical studies have shown that heparan sulfate glycosaminoglycans are involved in signaling by fibroblast growth factor receptors, but evidence for such a requirement in an intact organism has not been available. We now demonstrate that sugarless and sulfateless mutant embryos have phenotypes similar to those lacking the functions of two Drosophila fibroblast growth factor receptors, Heartless and Breathless. Moreover, both Heartless- and Breathless-dependent MAPK activation is significantly reduced in embryos which fail to synthesize heparan sulfate glycosaminoglycans. Consistent with an involvement of Sulfateless and Sugarless in fibroblast growth factor receptor signaling, a constitutively activated form of Heartless partially rescues sugarless and sulfateless mutants, and dosage-sensitive interactions occur between heartless and the heparan sulfate glycosaminoglycan biosynthetic enzyme genes. We also find that overexpression of Branchless, the Breathless ligand, can partially overcome the requirement of Sugarless and Sulfateless for Breathless activity. These results provide the first genetic evidence that heparan sulfate glycosaminoglycans are essential for fibroblast growth factor receptor signaling in a well defined developmental context, and support a model in which heparan sulfate glycosaminoglycans facilitate fibroblast growth factor ligand and/or ligand-receptor oligomerization.

Dual functions of the heartless fibroblast growth factor receptor in development of the Drosophila embryonic mesoderm.

The Drosophila embryonic mesoderm forms by invagination of the ventral-most blastoderm cells. Subsequent development of this germ layer involves the dorsolateral migration of the internalized cells and expansion by cell division, followed by the specification of particular cell fates through the coordinate actions of both intrinsic and extrinsic regulatory mechanisms. The latter include several intercellular signals that function across germ layers. These processes combine to generate a diversity of mesodermal sub-types, including the cardial and pericardial cells of the heart or dorsal vessel, a complete set of somatic muscle founders each with its unique identity, a population of cells that form the visceral musculature, and other cells that develop into hemocytes and the fat body. Here, we review recent evidence for the involvement of a fibroblast growth factor receptor (FGFR) encoded by the heartless (htl) gene in early directional migration of the Drosophila mesoderm. In addition, we provide new data that 1) demonstrate a second role for Htl in promoting the specification of the precursors to certain cardiac and somatic muscle cells in the Drosophila embryo, independent of its cell migration function, 2) suggest that Ras and at least one other signal transduction pathway act downstream of Htl, and 3) establish a functional relationship between the Ras pathway and Tinman (Tin), a homeodomain factor that is essential for specifying some of the same dorsal mesodermal cells that are dependent on Htl. Finally, parallels between requirements for FGFR signaling in Drosophila and vertebrate mesoderm development are considered.

[Complex instability in the system of hobo and stalker mobile element interaction in Drosophila melanogaster]. / Mnozhestvennaia nestabil'nost' v sisteme vzaimodeistviia mobil'nykh élementov hobo i stalker u Drosophila melanogaster.

A number of mutations in different Drosophila loci resulted from the relationship between hobo and stalker mobile elements. In this investigation an insertion from the parential white mutation-waG-was cloned. And the Doc element, that is the reason of the mutation, is not moving in the observed instability system. But transpositions of the copia-like elements (e.g. mdg1, 2, 3 and copia) were shown in this system. A cases of chromosomal rearrangements and abnormal recombination in compound with transpositions of different mobile elements were found. Thus, the system of instability could be explained in terms of universal mechanism which involved both transpositions and recombinations phenomena.

[Participation of mobile element hobo in transposition events in the long-term instability system of Drosophila melanogaster]. / Uchastie mobil'nogo élementa hobo v transpozitsionnykh sobytiiakh v sisteme linii prodlennoi nestabil'nosti u Drosophila melanogaster.

The lines with an active hobo elements as well as those without any hobo fragments were hybridized with the y2sc1waG line. This resulted in the appearance of a number of mutations at the white, miniature, and some other loci. The authors analysed, in which way the hobo transposable elements take part in mutagenesis in these crosses. Most of the white mutants obtained were analysed and transpositions of hobo and Stalker elements were demonstrated. Both independent and simultaneous transpositions were found. It was shown by means of the Southern blot analysis that additional hobo or Stalker insertion into or close to the parental unknown waG insertion resulted in mutant white phenotype's shift toward both extreme and partial reversion. Possible participation in mutagenesis of other mobile elements is also under debate.

[Properties of super unstable mutations in the Drosophila melanogaster yellow locus]. / Svoistva supernestabil'nykh mutatsii v lokuse yellow Drosophila melanogaster.

The properties of super-unstable systems of the white, singed and ocetilless loci obtained as a result of P-M dysgenesis induction in the strains with a mobilized Stalker were described earlier. In the studies of super-instability in ocetilless locus, six super-unstable mutations in the yellow locus were obtained. Detailed genetic analysis was performed resulting in isolation of 80 alleles with different phenotype expression. In general, super-instability in the yellow locus reminds that in the white and ocetilless loci. Most of alleles are highly unstable possessing a characteristic pattern of mutation changes. Also, sub-systems were found in the yellow super-unstable system. Each consists of several mutually inter-converting alleles which possess a characteristic phenotype, mode and rate of mutation changes.

[Superunstable systems in Drosophila melanogaster. Analysis of mutations in signed and cut loci]. / Supernestabil'nye sistemy u Drosophila melanogaster. Analiz mutatsii v lokusakh signed i cut.

The lines of the M'-cytotype characterized by a long-term instability (which was shown to be conditioned by transpositions of the new mobile element, Stalker) were hybridized with the P-line. This resulted in the appearance of a number of superunstable mutations at the yellow, white, singed, ocelliless and some other loci. The authors analyzed four independently obtained families of superunstable mutations at the singed locus. A wide spectrum of derivatives and high frequency of mutations were demonstrated, as well as the regularities of allelic transitions. Besides this, mutagenesis at the cut locus was observed in the chromosomes carrying sn mutations with frequency of 5.05 x 10(4). By means of the blot analysis it has been shown that most of ct mutations are intragenic deficiencies, ranging from 1.3 to 3 Kb, whose appearance is, conceivably, attributed to the inaccuracy of the insertion excision (the insertion is present but fails to alter the phenotype) at the cut locus of the chromosomes with the superunstable sn-alleles. In the lines with the sn- and ct-mutations the transpositions of the P-element and the Stalker were found, which indicates their involvement in mutagenesis. The authors discuss possible effects of inserting the complicated constructions, based on the combinations of P-element and the Stalker, on the induction of superinstability.