Characterization of the major hnRNP proteins from Drosophila melanogaster

To better understand the role(s) of hnRNP proteins in the process of mRNA formation, we have identified and characterized the major nuclear proteins that interact with hnRNAs in Drosophila melanogaster. cDNA clones of several D. melanogaster hnRNP proteins have been isolated and sequenced, and the genes encoding these proteins have been mapped cytologically on polytene chromosomes. These include the hnRNP proteins hrp36, hrp40, and hrp48, which together account for the major proteins of hnRNP complexes in D. melanogaster (Matunis et al., 1992, accompanying paper). All of the proteins described here contain two amino-terminal RNP consensus sequence RNA-binding domains and a carboxyl-terminal glycine-rich domain. We refer to this configuration, which is also found in the hnRNP A/B proteins of vertebrates, as 2 x RBD-Gly. The sequences of the D. melanogaster hnRNP proteins help define both highly conserved and variable amino acids within each RBD and support the suggestion that each RBD in multiple RBD-containing proteins has been conserved independently and has a different function. Although 2 x RBD-Gly proteins from evolutionarily distant organisms are conserved in their general structure, we find a surprising diversity among the members of this family of proteins. A mAb to the hrp40 proteins crossreacts with the human A/B and G hnRNP proteins and detects immunologically related proteins in divergent organisms from yeast to man. These data establish 2 x RBD-Gly as a prevalent hnRNP protein structure across eukaryotes. This information about the composition of hnRNP complexes and about the structure of hnRNA-binding proteins will facilitate studies of the functions of these proteins.     

A Drosophila melanogaster H3.3 cDNA encodes a histone variant identical with the vertebrate H3.3.

A cDNA encoding an H3.3 histone variant in Drosophila melanogaster predicts a protein with an amino acid (aa) sequence identical with that in vertebrates. The D. melanogaster H3.3 nucleotide (nt) sequence has diverged significantly from that of both the H3.3 gene of vertebrates and the H3.1 gene of D. melanogaster, largely through third nt changes in its codons. The perfect H3.3 aa sequence conservation between organisms as phylogenetically divergent as vertebrates and flies suggests that the H3.3 histone variant itself is an important structural component of chromatin, apart from the value of its replication-independent expression pattern.     

Identification of a fibroblast growth factor-binding protein in Drosophila melanogaster.

As assessed by competitive binding and protein-crosslinking experiments, Drosophila melanogaster cells possess basic fibroblast growth factor (bFGF)-specific binding proteins that are similar to FGF receptors on vertebrate cells in molecular weight and binding affinity; these D. melanogaster cells, however, have no detectable binding proteins for acidic fibroblast growth factor (aFGF). Consistent with the presence of bFGF-specific binding proteins, D. melanogaster cells degrade bFGF but not aFGF. These results indicate the conservation of heparin-binding growth factors and receptors between vertebrates and D. melanogaster.     

Lineage-specific expansion of the zinc finger associated domain ZAD

The zinc finger associated domain (ZAD), present in almost 100 distinct proteins, characterizes the largest subgroup of C2H2 zinc finger proteins in Drosophila melanogaster and was initially found to be encoded by arthropod genomes only. Here, we report that the ZAD was also present in the last common ancestor of arthropods and vertebrates, and that vertebrate genomes contain a single conserved gene that codes for a ZAD-like peptide. Comparison of the ZAD proteomes of several arthropod species revealed an extensive and species-specific expansion of ZAD-coding genes in higher holometabolous insects, and shows that only few ZAD-coding genes with essential functions in Drosophila melanogaster are conserved. Furthermore, at least 50% of the ZAD-coding genes of Drosophila melanogaster are expressed in the female germline, suggesting a function in oocyte development and/or a requirement during early embryogenesis. Since the majority of the essential ZAD coding genes of Drosophila melanogaster were not conserved during arthropod or at least during insect evolution, we propose that the LSE of ZAD-coding genes shown here may provide the raw material for the evolution of new functions that allow organisms to pursue novel evolutionary paths.     

The evolution of antifungal peptides in Drosophila

An essential component of the immune system of animals is the production of antimicrobial peptides (AMPs). In vertebrates and termites the protein sequence of some AMPs evolves rapidly under positive selection, suggesting that they may be coevolving with pathogens. However, antibacterial peptides in Drosophila tend to be highly conserved. We have inferred the selection pressures acting on Drosophila antifungal peptides (drosomycins) from both the divergence of drosomycin genes within and between five species of Drosophila and polymorphism data from Drosophila simulans and D. melanogaster. In common with Drosophila antibacterial peptides, there is no evidence of adaptive protein evolution in any of the drosomycin genes, suggesting that they do not coevolve with pathogens. It is possible that this reflects a lack of specific fungal and bacterial parasites in Drosophila populations. The polymorphism data from both species differed from neutrality at one locus, but this was not associated with changes in the protein sequence. The synonymous site diversity was greater in D. simulans than in D. melanogaster, but the diversity both upstream of the genes and at nonsynonymous sites was similar. This can be explained if both upstream and nonsynonymous mutations are slightly deleterious and are removed more effectively from D. simulans due to its larger effective population size.     

天然免疫系统新成员Akirin的研究进展

天然免疫系统是多细胞动物抵御细菌感染的第一道防线。Akirin是新近发现于果蝇中的天然免疫系统新成员,它在果蝇免疫缺陷(Imd)通路中发挥重要作用。Akirin同源基因广泛存在于从低等多细胞生物到高等脊椎动物中,进化上高度保守。已有的研究表明:Akirin在果蝇Imd通路和脊椎动物TLR通路下游,与NF-κB家族转录因子形成复合物,参与调控免疫相关靶基因的转录,是天然免疫调控机制中不可或缺的转录因子,其过表达或缺失直接影响动物对细菌的防御能力。近年来,Akirin在相关信号通路中的功能研究取得重大进展。该文对Akirin的结构、参与天然免疫的分子调控机制以及基因进化等方面进行综述。     

Signal pathway of insulin and insulin-like growth factor 1 (IGF-1) as a potential regulator of lifespan

The experimental material accumulated for two decades allows concluding that regulation of lifespan has hormonal control based on the evolutionary conservative insulin/IGF-1 receptor signal pathway. Data obtained on the commonly accepted models of longevity - nematode Caenorhabditis elegans, Drosophila Drosophila melanogaster, and rodents - demonstrate that reduction of the insulin/IGF- 1 signal pathway leads to an increase of the lifespan. There is shown involvement of the longevity mechanism of a large group of genes whose products perform control of metabolism, alimentary behavior, reproduction, resistance to oxidative stress. Discussed in this review are current concepts of the insulin/IGF-1 signal system as a regulatory "longevity module" and of its possible role in prolongation of life in the higher vertebrates, including human.     

Lectin-like proteins in model organisms: implications for evolution of carbohydrate-binding activity.

Classes of intracellular lectins that recognize core-type structures and mediate intracellular glycoprotein trafficking are present in vertebrates, model invertebrates such as Caenorhabditis elegans and Drosophila melanogaster, plants, and yeasts. Lectins that recognize more complex structures at the cell surface, such as C-type lectins and galectins, are also found in invertebrate organisms as well as vertebrates, but the functions of these proteins have evolved differently in different animal lineages.     

Drosophila snRNP associated protein P11 which specifically binds to heat shock puff 93D reveals strong homology with hnRNP core protein A1.

We have isolated cDNAs coding for a ribonucleoprotein of Drosophila melanogaster that is distinguished by its nearly exclusive presence at only one of the several heat shock puffs in polytene chromosomes of third instar larvae. We determined the nucleotide sequence and deduced the corresponding amino acid sequence. Its coding capacity for a 39 kDa protein is consistent with the size of the protein detected by the monoclonal antibody P11 used for expression cloning. Our results show that the P11 protein belongs to the category of hnRNP proteins of bipartite structure: the amino-terminal half contains two RNA binding domains and the carboxyterminal half is rich in glycine residues. Analysis of the genomic structure revealed two introns located within the coding portion of the gene and a third one in the 3'untranslated region. We detect two different polyadenylation sites as a result of alternative termination-polyadenylation. Its strong sequence homology with hnRNP A1 protein and its previously shown association with snRNP particles indicates that a typical hnRNP protein may also exist in a complex with snRNP particles. The P11 sequence corresponds to the Hrb87F sequence that was recently described by Haynes et al. (1) as hnRNP A related gene.     

About the origin of retroviruses and the co-evolution of the gypsy retrovirus with the Drosophila flamenco host gene

The gypsy element of Drosophila melanogaster is the first retrovirus identified so far in invertebrates. According to phylogenetic data, gypsy belongs to the same group as the Ty3 class of LTR-retrotransposons, which suggests that retroviruses evolved from this kind of retroelements before the radiation of vertebrates. There are other invertebrate retroelements that are also likely to be endogenous retroviruses because they share with gypsy some structural and functional retroviral-like characteristics. Gypsy is controlled by a Drosophila gene called flamenco, the restrictive alleles of which maintain the retrovirus in a repressed state. In permissive strains, functional gypsy elements transpose at high frequency and produce infective particles. Defective gypsy proviruses located in pericentromeric heterochromatin of all strains seem to be very old components of the genome of Drosophila melanogaster, which indicates that gypsy invaded this species, or an ancestor, a long time ago. At that time, Drosophila melanogaster presumably contained permissive alleles of the flamenco gene. One can imagine that the species survived to the increase of genetic load caused by the retroviral invasion because restrictive alleles of flamenco were selected. The characterization of a retrovirus in Drosophila, one of the most advanced model organisms for molecular genetics, provides us with an exceptional clue to study how a species can resist a retroviral invasion. This revised version was published online in August 2006 with corrections to the Cover Date.