Bacterial avidins are a widely distributed protein family in Actinobacteria, Proteobacteria and Bacteroidetes

Background Avidins are biotin-binding proteins commonly found in the vertebrate eggs. In addition to streptavidin from Streptomyces avidinii, a growing number of avidins have been characterized from divergent bacterial species. However, a systematic research concerning their taxonomy and ecological role has never been done. We performed a search for avidin encoding genes among bacteria using available databases and classified potential avidins according to taxonomy and the ecological niches utilized by host bacteria. Results Numerous avidin-encoding genes were found in the phyla Actinobacteria and Proteobacteria. The diversity of protein sequences was high and several new variants of genes encoding biotin-binding avidins were found. The living strategies of bacteria hosting avidin encoding genes fall mainly into two categories. Human and animal pathogens were overrepresented among the found bacteria carrying avidin genes. The other widespread category were bacteria that either fix nitrogen or live in root nodules/rhizospheres of plants hosting nitrogen-fixing bacteria. Conclusions Bacterial avidins are a taxonomically and ecologically diverse group mainly found in Actinobacteria, Proteobacteria and Bacteroidetes, associated often with plant invasiveness. Avidin encoding genes in plasmids hint that avidins may be horizontally transferred. The current survey may be used as a basis in attempts to understand the ecological significance of biotin-binding capacity.

Knock out of Specific Maternal Vitellogenins in Zebrafish (Danio Rerio) Evokes Vital Changes in Egg Proteomic Profiles that resemble the Phenotype of Poor Quality Eggs

Background We previously reported the results of CRISPR/Cas9 knock-out (KO) of type-I and type-III vitellogenins (Vtgs) in zebrafish, which provided the first experimental evidence of essentiality and disparate functioning of specific types of Vtg at different times during vertebrate development. However, the lack of knowledge on specific contributions of different types of Vtg to molecular functions related to major developmental processes remained to be investigated. The present study employed liquid chromatography and tandem mass spectrometry (LC-MS/MS) to observe proteomic profiles of zebrafish eggs lacking three type-I Vtgs (Vtg 1, 4 and 5) simultaneously (vtg1-KO), or lacking type III Vtg (vtg3) only (vtg3-KO), as compared to those of wild type (Wt) eggs. Obtained spectra were searched against a zebrafish proteome database and identified proteins were quantified based on normalized spectral counts.Results The vtg-KO in zebrafish revealed impaired proteomes of 1 hour post fertilization (hpf) zebrafish eggs which were highly resembled the proteomic phenotype of poor quality eggs of the same developmental stage reported in our prior studies. Proteomic profiles of vtg-KO eggs and perturbations in abundances of hundreds of proteins revealed unique, noncompensable contributions of multiple Vtgs in protein homeostasis (synthesis and degradation) and in energy homeostasis even after zygotic genome activation. Increase in endoplasmic reticulum stress, Redox/Detox activities, glycolysis/gluconeogenesis, enrichment in cellular proliferation and human neurodegenerative disease related mechanisms in both vtg1- and vtg3-KO eggs point to severe molecular changes and consecutive dysfunctions in the abovementioned cellular activities. Distinctive increase in apoptosis and Parkinson disease pathways and decrease in lipid metabolism related activities in vtg3-KO eggs implies compelling roles of Vtg3, the least abundant form of Vtgs in vertebrate eggs, in mitochondrial activities. Several differentially abundant proteins representing the altered molecular mechanisms were unveiled to be considered as strong candidate markers to study details of these mechanisms during early embryonic development in zebrafish and potentially other vertebrates. Conclusions These findings indicate that the global egg proteome is subject to extensive modification depending on the presence or absence of specific Vtgs and that these modifications can have a major impact on developmental competence.

Emi2-mediated Inhibition of E2-substrate Ubiquitin Transfer by the Anaphase-promoting Complex/Cyclosome through a D-Box–independent Mechanism

Vertebrate eggs are arrested at Metaphase II by Emi2, the meiotic anaphase-promoting complex/cyclosome (APC/C) inhibitor. Although the importance of Emi2 during oocyte maturation has been widely recognized and its regulation extensively studied, its mechanism of action remained elusive. Many APC/C inhibitors have been reported to act as pseudosubstrates, inhibiting the APC/C by preventing substrate binding. Here we show that a previously identified zinc-binding region is critical for the function of Emi2, whereas the D-box is largely dispensable. We further demonstrate that instead of acting through a “pseudosubstrate” mechanism as previously hypothesized, Emi2 can inhibit Cdc20-dependent activation of the APC/C substoichiometrically, blocking ubiquitin transfer from the ubiquitin-charged E2 to the substrate. These findings provide a novel mechanism of APC/C inhibition wherein the final step of ubiquitin transfer is targeted and raise the interesting possibility that APC/C is inhibited by Emi2 in a catalytic manner.

Emi2 Inhibition of the Anaphase-promoting Complex/Cyclosome Absolutely Requires Emi2 Binding via the C-Terminal RL Tail

Emi2 (also called Erp1) inhibits the anaphase-promoting complex/cyclosome (APC/C) and thereby causes metaphase II arrest in unfertilized vertebrate eggs. Both the D-box and the zinc-binding region (ZBR) of Emi2 have been implicated in APC/C inhibition. However, it is not well known how Emi2 interacts with and hence inhibits the APC/C. Here we show that Emi2 binds the APC/C via the C-terminal tail, termed here the RL tail. When expressed in Xenopus oocytes and egg extracts, Emi2 lacking the RL tail fails to interact with and inhibit the APC/C. The RL tail itself can directly bind to the APC/C, and, when added to egg extracts, either an excess of RL tail peptides or anti-RL tail peptide antibody can dissociate endogenous Emi2 from the APC/C, thus allowing APC/C activation. Furthermore, and importantly, the RL tail–mediated binding apparently promotes the inhibitory interactions of the D-box and the ZBR (of Emi2) with the APC/C. Finally, Emi1, a somatic paralog of Emi2, also has a functionally similar RL tail. We propose that the RL tail of Emi1/Emi2 serves as a docking site for the APC/C, thereby promoting the interaction and inhibition of the APC/C by the D-box and the ZBR.

Consequences of prenatal androgen exposure for the reproductive performance of female pheasants ( Phasianus colchicus )

Maternal hormones in vertebrate eggs can mediate important forms of maternal effects. However, the function of hormone transfer to the eggs is still debated, especially because long-term fitness consequences have been little studied. We investigated the effect of prenatal exposure to physiologically elevated yolk testosterone (T) levels on reproduction of female pheasants ( Phasianus colchicus ) in captivity. We found that females hatching from T-injected eggs (T-females) had a lower egg-laying rate than controls, and their eggs were more frequently infertile than those laid by control females. There were no effects of prenatal maternal treatment on egg size and yolk T concentration, but eggs carrying a female embryo laid by T-females had smaller yolks than eggs with a male embryo, while there was no sex difference in yolk size among the eggs laid by control females. Progeny sex ratio was unaffected by maternal treatment. These findings suggest that the transfer of high androgen levels to the eggs by the mother is constrained by complex trade-offs between direct effects on her daughters’ reproduction and by trans-generational differential consequences on male and female descendants.

Fyn kinase–tubulin interaction during meiosis of rat eggs

Prior to fertilization, the spindle of vertebrate eggs must remain stable and well organized during the second meiotic meta-phase arrest (MII). In a previous study we have determined that the completion of meiosis is a Src family kinase (SFK)-dependent event. In the current study we have used the SFK inhibitors, SU6656 and PP2, and demonstrated that inhibition of SFKs caused the formation of a disorganized spindle. The observation that proper organization of an MII spindle is an SFK-dependent process, combined with our previous finding that Fyn kinase is localized at the microtubules (MTs), prompted us to examine the potential role of Fyn in MT signaling. Our results show an association between Fyn and tubulin, the ability of Fyn to phosphorylate tubulinin vitroand stimulation of meiosis completion by injection of a constitutively active form of Fyn (CAF).We suggested that SFKs mediate significant functions during the organization of the MII spindle. In view of CAF injection experiments, and of the pronounced concentration of Fyn kinase at the spindle, we propose that Fyn may play an important role in some aspects of the spindle functions, possibly those involving the MTs.