The Maternal-to-Zygotic Transition Targets Actin to Promote Robustness during Morphogenesis

Robustness is a property built into biological systems to ensure stereotypical outcomes despite fluctuating inputs from gene dosage, biochemical noise, and the environment. During development, robustness safeguards embryos against structural and functional defects. Yet, our understanding of how robustness is achieved in embryos is limited. While much attention has been paid to the role of gene and signaling networks in promoting robust cell fate determination, little has been done to rigorously assay how mechanical processes like morphogenesis are designed to buffer against variable conditions. Here we show that the cell shape changes that drive morphogenesis can be made robust by mechanisms targeting the actin cytoskeleton. We identified two novel members of the Vinculin/α-Catenin Superfamily that work together to promote robustness during Drosophila cellularization, the dramatic tissue-building event that generates the primary epithelium of the embryo. We find that zygotically-expressed Serendipity-α (Sry-α) and maternally-loaded Spitting Image (Spt) share a redundant, actin-regulating activity during cellularization. Spt alone is sufficient for cellularization at an optimal temperature, but both Spt plus Sry-α are required at high temperature and when actin assembly is compromised by genetic perturbation. Our results offer a clear example of how the maternal and zygotic genomes interact to promote the robustness of early developmental events. Specifically, the Spt and Sry-α collaboration is informative when it comes to genes that show both a maternal and zygotic requirement during a given morphogenetic process. For the cellularization of Drosophilids, Sry-α and its expression profile may represent a genetic adaptive trait with the sole purpose of making this extreme event more reliable. Since all morphogenesis depends on cytoskeletal remodeling, both in embryos and adults, we suggest that robustness-promoting mechanisms aimed at actin could be effective at all life stages.     

Characterization of a High Affinity Phytochelatin Synthase from The Cd‐Utilizing Marine Diatom Thalassiosira pseudonana

Phytochelatin synthase (PC synthase) is the enzyme that catalyzes the production of phytochelatins, peptides of the structure (γ‐Glu‐Cys)_n‐Gly, where n = 2–11, from the sulfhydryl‐containing tripeptide glutathione, in response to elevated metal exposure. Biochemical utilization of Cd in the marine diatom Thalassiosira weissfloggi, as well as unusually high ratios of PC to Cd in some Thalassiosira species including T. pseudonana Hasle et Heimdal, motivated the characterization of T. pseudonana PC synthase 1 (TpPCS1). This enzyme is the product of one of three genes in the T. pseudonana genome predicted to encode for a PC synthase based on its homology to canonical PC synthases previously examined. TpPCS1 was cloned, expressed in Escherichia coli and purified under both aerobic and anaerobic conditions. TpPCS1 exhibits several characteristics that set it distinctly apart from the well‐studied PC synthase, Arabidopsis thaliana PCS1 (AtPCS1). It is extremely sensitive to oxidation, which suppresses activity, and it is readily inhibited by the addition of Cd in the absence of thiolate ligands. TpPCS1 also has significantly greater affinity for one of its key substrates, the bis‐glutathionato‐Cd complex. TpPCS1 kinetics is best described by a ternary complex model, as opposed to the ping‐pong model used to describe AtPCS1 kinetics. The findings indicate that although the function of TpPCS1 is synonymous to that of AtPCS1, its divergent biochemistry suggests adaptation of this enzyme to the distinct trace metal chemistry of the marine environment and the unique physiological needs of T. pseudonana.     

Integrative analyses on Western Palearctic Lasiommata reveal a mosaic of nascent butterfly species

Satyrinae butterflies occurring in the Mediterranean apparently have reduced gene flow over sea straits, and for several species, recent wide-scale biodiversity surveys indicate the existence of divergent mitochondrial lineages. Here, we apply an integrative approach and examine the phylogeography of the genus Lasiommata in the Western Palearctic. Our research comprised molecular analyses (mitochondrial and nuclear DNA) and geometric morphometrics (wings and genitalia) for two main species groups, and a comparative GMYC analysis, based on COI, of all the tribes within Satyrinae from this region. The GMYC approach revealed a particularly fast coalescence rate in the Parargina subtribe. The Lasiommata group was divided into 12 evolutionary significant units: six clades for the L. maera species group, five for the L. megera species group, and one for L. petropolitana, with divergences of about 1%. The patterns of COI were mirrored by ITS2 in L. maera, but the two markers were generally inconsistent in L. megera. On the contrary, morphological differences were coherent with the results of COI for L. megera, but less clearly so for L. maera. L. paramegaera and L. meadewaldoi were considerably differentiated for all the analyzed markers and likely proceeded faster in the process of speciation because of geographic isolation and reduced effective population size, rendering the rest paraphyletic. Our study illustrates the continuous nature of speciation and the difficulties of delimiting species. In Lasiommata, the recognition of taxa as diverging lineages or distinct, possibly paraphyletic species, mostly depends on the criteria adopted by different species concepts.     

Population genomics reveals evolution and variation of Saccharomyces cerevisiae in the human and insects gut

The quest to discover the variety of ecological niches inhabited by Saccharomyces cerevisiae has led to research in areas as diverse as wineries, oak trees and insect guts. The discovery of fungal communities in the human gastrointestinal tract suggested the host's gut as a potential reservoir for yeast adaptation. Here, we report the existence of yeast populations associated with the human gut (HG) that differ from those isolated from other human body sites. Phylogenetic analysis on 12 microsatellite loci and 1715 combined CDSs from whole-genome sequencing revealed three subclusters of HG strains with further evidence of clonal colonization within the host's gut. The presence of such subclusters was supported by other genomic features, such as copy number variation, absence/introgressions of CDSs and relative polymorphism frequency. Functional analysis of CDSs specific of the different subclusters suggested possible alterations in cell wall composition and sporulation features. The phenotypic analysis combined with immunological profiling of these strains further showed that sporulation was related with strain-specific genomic characteristics in the immune recognition pattern. We conclude that both genetic and environmental factors involved in cell wall remodelling and sporulation are the main drivers of adaptation in S. cerevisiae populations in the human gut.     

Polyclonal B Cell Activation by Cell Wall Preparations of Gram-Positive Bacteria

The effects of polyclonal B cell activation (PBA) of cell walls and their cell wall fractions obtained from several kinds of gram-positive bacteria were studied using the anti-sheep red blood cell (SRBC) or anti-trinitrophenylated (TNP) SRBC plaque forming cell (PFC) responses of cultured spleen cells from Balb/c, athymic nu/nu, their littermates (nu/+), C3H/He (LPS-responder), C3H/HeJ (LPS-non-responder), (CBA/N × Balb/c) F1 male with an X-linked defect in B cell function and the F1 female mice. The cell walls of Staphylococcus epidermidis (ATCC 155), Lactobacillus plantarum (ATCC 8014), Micrococcus lysodeikticus (NCTC 2665), Mycobacterium rhodochrous (ATCC 184), Streptomyces gardneri (ATCC 23911) and Nocardia corynebacteriodes (ATCC 14898) had the ability to induce polyclonal B cell responses in the spleen cells of Balb/c, nu/nu, nu/+, C3H/He and C3H/HeJ mice. The cell wall fractions prepared by enzymatic digestion from the cell walls of S. epidermidis, S. gardneri or N. corynebacteriodes were also capable of inducing polyclonal B cell responses. The responses of spleen cells from (CBA/N × Balb/c) F1 male mice to these active preparations, except the cell walls of M. rhodochrous, were much lower than those of the F1 female mice. These findings indicate that the majority of the cell wall preparations lacks PBA ability for spleen cells with the CBA/N defect, except for the cell walls of M. rhodochrous which possess this ability. The PBA-ability of synthetic peptidoglycan, muramyl dipeptide (N-acetylmuramyl-L -alanyl-D -isoglutamine, MDP), was also examined, and a similar activity was observed in MDP.     

Multiple Syringe Inoculator for Agar Plates

The design and operation of a manually operated multiple syringe inoculator was described. Either 9 or 21 inoculations of constant volume could be made simultaneously. Up to 100 plates could be inoculated in 15 min with excellent reproducibility. No contact occurred between the inoculating needles and the agar surface. Construction was simple and inexpensive, with minimal maintenance.     

Immunosuppressive Effect of Bacterial Lipopolysaccharide on Antibody Response

Injection of endotoxins (bacterial lipopolysaccharide: LPS) several days prior to immunization causes the suppression of antibody response. The suppressive effects of several kinds of LPS preparations on the plaque-forming cell (PFC) antibody response in the spleen of mice were examined after immunization with sheep red blood cells (SRBC). Glycolipids obtained from heptoseless mutants (Re form) of salmonella or its lipid A preparation coupled artificially with bovine serum albumin (BSA) are capable, like LPS obtained from a wild type (S form) strain, of inducing suppression of the PFC response, while alkaline-detoxified LPS can not. The refractory periods of the PFC response induced by LPS injection last only a few days. However, the use of cyclophosphamide (CY) together with LPS can extend the refractory periods of antigenic stimulation for several weeks. Injections of LPS and CY can also induce unresponsive states of OH agglutinin antibody response to antigenic stimulation with formalin-killed organisms of Escherichia coli or Salmonella enteritidis (presumably both thymus-independent antigens). These unresponsive states induced by LPS and CY are easily terminated by a transfer of syngeneic bone marrow cells but not by thymocyte transfer.     

Genetic structure and management of the Neotropical migratory fish Megaleporinus obtusidens on a highly impacted river basin

Habitat fragmentation caused by hydroelectric dams has depleted fish populations worldwide. Restocking actions are usually adopted to recover those populations, but hatchery management protocols rarely guarantee the maintenance of genetic diversity and a balanced contribution among captive breeders each generation. Here, a set of 10 microsatellite markers was used to assess the genetic diversity (average allelic richness A_R?=?10.87 and expected heterozygosity H_E?=?0.742, respectively) and structuring of Megaleporinus obtusidens, a migratory freshwater fish inhabiting over 2500 km of the São Francisco River in Brazil. Three main genetic clusters were identified in this species across the river basin that could be related to the sharply different climatic and hydrologic regimes from the Upper to the Lower course. A significant reduction (> 50%) in genetic diversity was observed in the broodstock when compared to their wild conspecifics, especially in the allelic richness. The information here presented will aid for management of genetic resources of this species in the São Francisco River taking as reference the genetic clusters identified. Furthermore, the results indicated that restocking is not necessary unless signals of population depletion occurs and, if so, hatchery reproductive protocols should rely on artificial fertilization rather than mass spawning.

     

Environmental degradation of streams leads to the loss of ecomorphologically similar fish species

Hydrobiologia - Human activities change the environmental conditions of streams and alter their assemblages. However, the environmental factors associated with the change in the ecomorphological...