High impact information on sqd

• One specific target, the hrp40/squid transcript, shows an altered pre-mRNA splicing pattern in PSI mutant testes [1].
• Specific isoforms of squid, a Drosophila hnRNP, perform distinct roles in Gurken localization during oogenesis [2].
• Thus, hrp45 behaves as an hnRNP protein linked to exon RNA (and perhaps also to the introns) rather than as a spliceosome component connected to the assembly and disassembly of spliceosomes [3].
• We identify the 50-kD protein as hrp48, a protein similar to the mammalian splicing factor hnRNP A1, and show that hrp48 recognizes specific nucleotides in a pseudo-5' splice site within the inhibitory element [4].
• We also show that Hrp59 binds preferentially to exonic splicing enhancers and our results provide new insights into the role of hnRNP M in splicing regulation [5].

Biological context of sqd

• We identified sqd in a screen for modifiers of the Protein Kinase A (PKA) oogenesis polarity phenotype [6].
• To better understand the relationship between hnRNP proteins and snRNP particles and their roles in mRNA formation, we have visualized them as they associate with nascent transcripts on the polytene chromosomes of Drosophila melanogaster salivary glands [7].
• Three other proteins present in the complex have been identified: X4/PEP (protein on ecdysone puffs), a 100-kDa zinc finger RNA-binding protein; the 70-kDa S5 protein, an as yet uncharacterized RNA-binding protein; and P11/Hrb87F, a 38-kDa RRM protein homologous to hnRNP protein A1 from mammals [8].
• Genuine hnRNP proteins were identified by several criteria, including nucleoplasmic localization, association with nascent transcripts, crosslinking to poly(A)-containing RNA in living cells, and amino acid sequence [9].
• The dynamic nuclear redistribution of an hnRNP K-homologous protein during Drosophila embryo development and heat shock. Flexibility of transcription sites in vivo [10].

Anatomical context of sqd

• The AP defects of sqd mutant oocytes resemble those of PKA mutants in several ways [6].
• We conclude that the hsromega-n transcripts play essential structural and functional roles in organizing and establishing the hnRNP-containing omega speckles and thus regulate the trafficking and availability of hnRNPs and other related RNA binding proteins in the cell nucleus [11].
• We suggest that a compromise in the activity of cyst cells due to the aberrant hnRNP distribution is responsible for the failure of individualization of sperms in hsromega05421; mutant testes [12].
• Essential role for a heterogeneous nuclear ribonucleoprotein (hnRNP) in oogenesis: hrp40 is absent from the germ line in the dorsoventral mutant squid [13].
• It has been shown to precipitate hnRNP particles from HeLa cells through a cross-reaction with the major 32,000- and 34,000-dalton hnRNP particle proteins [14].

Associations of sqd with chemical compounds

• Here we use band shift experiments to show that RNA binding patterns are altered when Sxl is combined with other proteins having similar glycine-rich domains, including mammalian heterogeneous nuclear (hn) RNP L and Drosophila Hrb87F (an hnRNP A/B homolog) [15].
• Tyrosine phosphorylation of a M(r) 38,000 A/B-type hnRNP protein selectively modulates its RNA binding [16].
• HnRNP from nitrogen frozen Drosophila melanogaster embryos were isolated in the presence of EDTA and EGTA cosedimenting in sucrose and density gradients like hnRNP from vertebrates [17].

Physical interactions of sqd

• The fusilli gene encodes a protein with RNA binding motifs related to those in mammalian hnRNP F and H, which play roles in regulated RNA splicing [18].

Regulatory relationships of sqd

• Furthermore, anterior patterning defects observed in embryos from sqd females expressing only the SqdS protein isoform suggest that Sqd may also play a role in the translational regulation of the mislocalized osk mRNA [19].

Other interactions of sqd

• We show that Sqd interacts with Hrb27C, an hnRNP previously implicated in splicing [20].
• In oocytes from sqd females, osk mRNA is not efficiently localized to the posterior pole, but rather accumulates at the anterior cortex [19].
• In situ immunocytochemical staining using antibodies against heterogenous nuclear RNA binding proteins (hnRNPs) like HRB87F, Hrp40, Hrb57A and S5 revealed that, in all cell types, all the hnRNPs gave a diffuse staining of chromatin areas and in addition, were present as large numbers of speckles [11].
• Numerous differences in the relative amounts of snRNP particles and hnRNP proteins on nascent transcripts are also observed [7].
• Immunoprecipitation studies using the hnRNP antibodies further demonstrated a physical association of hnRNPs and hsromega transcripts [11].

Analytical, diagnostic and therapeutic context of sqd

• We report on the molecular cloning and intracellular localization of a heterogeneous nuclear ribonucleoprotein (hnRNP), Ct-hrp45, one of the major components of pre-mRNP particles in Chironomus tentans [3].
• Candidate hnRNP proteins were purified from D. melanogaster embryos by ssDNA affinity chromatography, and mAbs were produced to many of the major proteins [9].
• In cultured oligodendrocytes, hnRNP A2 was demonstrated by confocal microscopy to be distributed throughout the nucleus, cell soma, and processes [21].
• We used two-dimensional (2-D) gel electrophoresis, matrix-assisted laser desorption ionization mass spectroscopy (MALDI-MS) and specific software for quantification. hnRNP A2/B1 was significantly increased in fetal DS brain (13.52+/-4.50) compared to controls (9.16+/-1.35), but both hnRNP H and H' were unchanged [22].

References