Positive selection is a general phenomenon in the evolution of abalone sperm lysin

Lysin is a 16kDa acrosomal protein used by abalone sperm to create a hole in the egg vitelline envelope (VE). The interaction of lysin with the VE is species-selective and is one step in the multistep fertilization process that restricts heterospecific (cross-species) fertilization. For this reason, the evolution of lysin could play a role in establishing prezygotic reproductive isolation between species. Previously, we sequenced sperm lysin cDNAs from seven California abalone species and showed that positive Darwinian selection promotes their divergence. In this paper an additional 13 lysin sequences are presented representing species from Japan, Taiwan, Australia, New Zealand, South Africa, and Europe. The total of 20 sequences represents the most extensive analysis of a fertilization protein to date. The phylogenetic analysis divides the sequences into two major clades, one composed of species from the northern Pacific (California and Japan) and the other composed of species from other parts of the world. Analysis of nucleotide substitution demonstrates that positive selection is a general process in the evolution of this fertilization protein. Analysis of nucleotide and codon usage bias shows that neither parameter can account for the robust data supporting positive selection. The selection pressure responsible for the positive selection on lysin remains unknown.      

Identification and Characterization of Toxigenic Fusaria Associated with Sorghum Grain Mold Complex in India

Fusarium species are dominant within the sorghum grain mold complex. Some species of Fusarium involved in grain mold complex produce mycotoxins, such as fumonisins. An attempt was made to identify Fusarium spp. associated with grain mold complex in major sorghum-growing areas in India through AFLP-based grouping of the isolates and to further confirm the species by sequencing part of α-Elongation factor gene and comparing the sequences with that available in the NCBI database. The dendrogram generated from the AFLP data clustered the isolates into 5 groups. Five species of Fusarium—F. proliferatum, F. thapsinum, F. equiseti, F. andiyazi and F. sacchari were identified based on sequence similarity of α-Elongation factor gene of the test isolates with those in the NCBI database. Fusarium thapsinum was identified as predominant species in Fusarium—grain mold complex in India and F. proliferatum as highly toxigenic for fumonisins production. Analysis of molecular variance (AMOVA) revealed 54% of the variation in the AFLP patterns of 63 isolates was due to the differences between Fusarium species, and 46% was due to differences between the strains within a species.     

Inducible Priming Phosphorylation Promotes Ligand-independent Degradation of the IFNAR1 Chain of Type I Interferon Receptor

Phosphorylation-dependent ubiquitination and ensuing down-regulation and lysosomal degradation of the interferon α/β receptor chain 1 (IFNAR1) of the receptor for Type I interferons play important roles in limiting the cellular responses to these cytokines. These events could be stimulated either by the ligands (in a Janus kinase-dependent manner) or by unfolded protein response (UPR) inducers including viral infection (in a manner dependent on the activity of pancreatic endoplasmic reticulum kinase). Both ligand-dependent and -independent pathways converge on phosphorylation of Ser⁵³⁵ within the IFNAR1 degron leading to recruitment of β-Trcp E3 ubiquitin ligase and concomitant ubiquitination and degradation. Casein kinase 1α (CK1α) was shown to directly phosphorylate Ser⁵³⁵ within the ligand-independent pathway. Yet given the constitutive activity of CK1α, it remained unclear how this pathway is stimulated by UPR. Here we report that induction of UPR promotes the phosphorylation of a proximal residue, Ser⁵³², in a pancreatic endoplasmic reticulum kinase-dependent manner. This serine serves as a priming site that promotes subsequent phosphorylation of IFNAR1 within its degron by CK1α. These events play an important role in regulating ubiquitination and degradation of IFNAR1 as well as the extent of Type I interferon signaling.     

Mitochondrial DNA and bindin gene sequence evolution among allopatric species of the sea urchin genus Arbacia

Sea urchins of the genus Arbacia (order Stirodonta) have discontinuous allopatric distributions ranging over thousands of kilometers. Mitochondrial DNA (mtDNA) sequences were used to reconstruct phylogenetic relationships of four Arbacia species and their geographic populations. There is little evidence of genetic structuring of populations within species, except in two cases at range extremes. The mtDNA sequence differentiation between species suggests that divergence occurred about 4-9 MYA. Gene sequences encoding the sperm protein bindin and its intron were obtained and compared with the mtDNA phylogeny. Sea urchins among the well-studied echinoid order Camarodonta, with degrees of mtDNA divergence similar to those of Arbacia species, are known to have remarkable variation in bindin. However, in Arbacia, little variation in deduced amino acid sequences of bindin was found, indicating that purifying selection acts on the protein. In contrast, bindin intron sequences showed much differentiation, including numerous insertion/deletions. Fertilization experiments performed between a divergent pair of Arbacia species from the Atlantic and Pacific Oceans revealed no evidence of blocks to gamete recognition. In Arbacia, fertilization specificities may have evolved relatively slowly as a result of extensive gene flow within species, greater functional constraint on the bindin polypeptide, or reduced selective pressure for species recognition in singly occurring species.      

Females of the sea urchin Strongylocentrotus purpuratus differ in the structures of their egg jelly sulfated fucans

The egg jelly coats of sea urchins contain sulfated fucans which bind to a sperm surface receptor glycoprotein to initiate the signal transduction events resulting in the sperm acrosome reaction. The acrosome reaction is an ion channel regulated exocytosis which is an obligatory event for sperm binding to, and fusion with, the egg. Approximately 90% of individual females of the sea urchin Strongylocentrotus purpuratus spawned eggs having only one of two possible sulfated fucan electrophoretic isotypes, a slow migrating (sulfated fucan I), or a fast migrating (sulfated fucan II) isotype. The remaining 10% of females spawned eggs having both sulfated fucan isotypes. The two sulfated fucan isotypes were purified from egg jelly coats and their structures determined by NMR spectroscopy and methylation analysis. Both sulfated fucans are linear polysaccharides composed of 1-->3-linked alpha-L-fucopyranosyl units. Sulfated fucan I is entirely sulfated at the O -2 position but with a heterogeneous sulfation pattern at O -4 position. Sulfated fucan II is composed of a regular repeating sequence of 3 residues, as follows: [3-alpha-L-Fuc p - 2,4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)-1-->3-alpha-L-Fuc p -4(OSO3)- 1]n. Both purified sulfated fucans have approximately equal potency in inducing the sperm acrosome reaction. The significance of two structurally different sulfated fucans in the egg jelly coat of this species could relate to the finding that the sperm receptor protein which binds sulfated fucan contains two carbohydrate recognition modules of the C-type lectin variety which differ by 50% in their primary structure.      

Production,characterization and applications of microbial cutinases

Cutinase is an enzyme that catalyses the degradation of insoluble biopolyester cutin, a structural component of plants. This enzyme has some properties of lipase and esterase. Because of its unique nature, it has potential of being an industrially important enzyme. Some of the useful applications of cutinase include hydrolysis of fats and oils, esterification and transesterification reactions. This enzyme is mainly produced by phytopathogenic fungi, but there are several bacteria which are known to produce cutinase. In this article, the production, purification, characterizations, enhancement of activity and stability, immobilization of the enzyme and its applications in various industries have been discussed.     

Differential roles for the interferon-inducible IFI16 and AIM2 innate immune sensors for cytosolic DNA in cellular senescence of human fibroblasts

The IFN-inducible IFI16 and AIM2 proteins act as innate immune sensors for cytosolic double-stranded DNA (dsDNA). On sensing dsDNA, the IFI16 protein induces the expression of IFN-β whereas the AIM2 protein forms an inflammasome, which promotes the secretion of IL-1β. Given that the knockdown of IFI16 expression in human diploid fibroblasts (HDF) delays the onset of cellular senescence, we investigated the potential roles for the IFI16 and AIM2 proteins in cellular senescence. We found that increased IFI16 protein levels in old (vs. young) HDFs were associated with the induction of IFN-β. In contrast, increased levels of the AIM2 protein in the senescent (vs. old) HDFs were associated with increased production of IL-1β. The knockdown of type I IFN-α receptor subunit, which reduced the basal levels of the IFI16 but not of the AIM2, protein delayed the onset of cellular senescence. Accordingly, increased constitutive levels of IFI16 and AIM2 proteins in ataxia telangiectasia mutated (ATM) HDFs were associated with the activation of the IFN signaling and increased levels of IL-1β. The IFN-β treatment of the young HDFs, which induced the expression of IFI16 and AIM2 proteins, activated a DNA damage response and also increased basal levels of IL-1β. Interestingly, the knockdown of AIM2 expression in HDFs increased the basal levels of IFI16 protein and activated the IFN signaling. In contrast, the knockdown of the IFI16 expression in HDFs decreased the basal and dsDNA-induced activation of the IFN signaling. Collectively, our observations show differential roles for the IFI16 and AIM2 proteins in cellular senescence and associated secretory phenotype.     

A SET-domain-independent role of WRAD complex in cell-cycle regulatory function of mixed lineage leukemia

MLL, the trithorax ortholog, is a well-characterized histone 3 lysine 4 methyltransferase that is crucial for proper regulation of the Hox genes during embryonic development. Chromosomal translocations, disrupting the Mll gene, lead to aggressive leukemia with poor prognosis. However, the functions of MLL in cellular processes like cell-cycle regulation are not well studied. Here we show that the MLL has a regulatory role during multiple phases of the cell cycle. RNAi-mediated knockdown reveals that MLL regulates S-phase progression and, proper segregation and cytokinesis during M phase. Using deletions and mutations, we narrow the cell-cycle regulatory role to the C subunit of MLL. Our analysis reveals that the transactivation domain and not the SET domain is important for the S-phase function of MLL. Surprisingly, disruption of MLL–WRAD interaction is sufficient to disrupt proper mitotic progression. These mitotic functions of WRAD are independent of SET domain of MLL and, therefore, define a new role of WRAD in subset of MLL functions. Finally, we address the overlapping and unique roles of the different SET family members in the cell cycle.