Impact of Daily Thermocycles on Hatching Rhythms,Larval Performance and Sex Differentiation of Zebrafish

In the wild, water temperature cycles daily: it warms up after sunrise, and cools rapidly after sunset. Surprisingly, the impact of such daily thermocycles during the early development of fish remains neglected. We investigated the influence of constant vs daily thermocycles in zebrafish, from embryo development to sexual differentiation, by applying four temperature regimens: two constant (24°C and 28°C) and two daily thermocycles: 28:24°C, TC (thermophase coinciding with daytime, and cryophase coinciding with night-time) and 24:28°C, CT (opposite to TC) in a 12:12 h light:dark cycle (LD). Embryo development was temperature-dependent but enhanced at 28°C and TC. Hatching rhythms were diurnal (around 4 h after lights on), but temperature- and cycle-sensitive, since hatching occurred sooner at 28°C (48 hours post fertilization; hpf) while it was delayed at 24°C (96 hpf). Under TC, hatching occurred at 72 hpf, while under CT hatching displayed two peaks (at 70 hpf and 94 hpf). In constant light (LL) or darkness (DD), hatching rhythms persisted with tau close to 24 h, suggesting a clock-controlled “gating” mechanism. Under 28°C or TC, larvae showed the best performance (high growth and survival, and low malformations). The sex ratio was strongly influenced by temperature, as the proportion of females was higher in CT and TC (79 and 83% respectively), contrasting with 28°C and 24°C, which led to more males (83 and 76%). Ovarian aromatase (cyp19a) expression in females was highest in TC and CT (6.5 and 4.6 fold higher than at 28°C, respectively); while anti-müllerian hormone (amh) expression in males increased in testis at 24°C (3.6 fold higher compared to TC) and particularly at 28°C (14.3 fold increase). Taken together, these findings highlight the key role of environmental cycles during early development, which shaped the daily rhythms in fish embryo and larvae, and ultimately influenced sex differentiation.     

Comparative analysis of inner cavities and ligand migration in non-symbiotic AHb1 and AHb2

This study reports a comparative analysis of the topological properties of inner cavities and the intrinsic dynamics of non-symbiotic hemoglobins AHb1 and AHb2 from Arabidopsis thaliana. The two proteins belong to the 3/3 globin fold and have a sequence identity of about 60%. However, it is widely assumed that they have distinct physiological roles. In order to investigate the structure–function relationships in these proteins, we have examined the bis-histidyl and ligand-bound hexacoordinated states by atomistic simulations using in silico structural models. The results allow us to identify two main pathways to the distal cavity in the bis-histidyl hexacoordinated proteins. Nevertheless, a larger accessibility to small gaseous molecules is found in AHb2. This effect can be attributed to three factors: the mutation Leu35(AHb1) → Phe32(AHb2), the enhanced flexibility of helix B, and the more favorable energetic profile for ligand migration to the distal cavity. The net effect of these factors would be to facilitate the access of ligands, thus compensating the preference for the fully hexacoordination of AHb2, in contrast to the equilibrium between hexa- and pentacoordinated species in AHb1. On the other hand, binding of the exogenous ligand introduces distinct structural changes in the two proteins. A well-defined tunnel is formed in AHb1, which might be relevant to accomplish the proposed NO detoxification reaction. In contrast, no similar tunnel is found in AHb2, which can be ascribed to the reduced flexibility of helix E imposed by the larger number of salt bridges compared to AHb1. This feature would thus support the storage and transport functions proposed for AHb2. This article is part of a Special Issue entitled: Oxygen Binding and Sensing Proteins.     

A new species of Borgatomelissa Patiny, 2000 from eastern Morocco: Borgatomelissa flavimaura n. sp. (Hymenoptera,Andrenidae)

Until now, two species of Borgatomelissa Patiny, 2000 have been described, both from loci typici located in the Near East and eastern Africa. Borgatomelissa brevipennis (Walker, 1871), the most widespread taxon, has also been found in the southern Sahelo-Sudanian belt of the Sahara. A third species from eastern Morocco is described in the present study: Borgatomelissa flavimaura n. sp. In addition to taxonomic insights, the new species sheds a new light on the biogeography of the genus.     

Environmental,geographical and time-related impacts on avian malaria infections in native and introduced populations of house sparrows (Passer domesticus), a globally invasive species

Aim

The increasing spread of vector-borne diseases has resulted in severe health concerns for humans, domestic animals and wildlife, with changes in land use and the introduction of invasive species being among the main possible causes for this increase. We explored several ecological drivers potentially affecting the local prevalence and richness of avian malaria parasite lineages in native and introduced house sparrows (Passer domesticus) populations.

Location

Global.

Time period

2002–2019.

Major taxa studied

Avian Plasmodium parasites in house sparrows.

Methods

We analysed data from 2,220 samples from 69 localities across all continents, except Antarctica. The influence of environment (urbanization index and human density), geography (altitude, latitude, hemisphere) and time (bird breeding season and years since introduction) were analysed using generalized additive mixed models (GAMMs) and random forests.

Results

Overall, 670 sparrows (30.2%) were infected with 22 Plasmodium lineages. In native populations, parasite prevalence was positively related to urbanization index, with the highest prevalence values in areas with intermediate urbanization levels. Likewise, in introduced populations, prevalence was positively associated with urbanization index; however, higher infection occurred in areas with either extreme high or low levels of urbanization. In introduced populations, the number of parasite lineages increased with altitude and with the years elapsed since the establishment of sparrows in a new locality. Here, after a decline in the number of parasite lineages in the first 30 years, an increase from 40 years onwards was detected.

Main conclusions

Urbanization was related to parasite prevalence in both native and introduced bird populations. In invaded areas, altitude and time since bird introduction were related to the number of Plasmodium lineages found to be infecting sparrows.     

Cytochemical Localization of Calcium in Prefusion Myoblasts from the Chick Embryo Myotome

Myoblast fusion is a Ca²⁺-dependent process. The aim of this report was to study the localization of Ca²⁺ in prefusion myoblasts from the brachial somites of chick embryos (51–108h of incubation), using the potassium pyroantimonate cytochemical method. When observed under a transmission electron microscope, electron-dense precipitates of Ca²⁺-antimonate were found in the basement membrane of the myotome, which separates the myotome from the adjacent mesenchyma. Within myoblasts, triads and sarcoplasmic reticulum associated with the first newly formed sarcomeres were observed, but a T-tubule network was not found. Moreover, Ca²⁺-antimonate precipitates were not observed in structures resembling T-tubules or sarcoplasmic reticulum. The results suggest that sarcomerogenesis and sarcoplasmic reticulum development occur simultaneously and that prefusion myoblasts have neither a T-tubule network nor Ca²⁺ deposits on sarcoplasmic reticulum. Small Ca²⁺ pools were found in the myoblast nuclei, cytoplasmic vesicles and mitochondrias. Ca²⁺-antimonate precipitates periodically distributed at the cell periphery, close to the cell membrane, were observed. These precipitates could represent internal Ca²⁺ stores located in the peripheral couplings and it is proposed that these pools of Ca²⁺ could be mobilized before fusion, leading to the increase in free intracellular Ca²⁺ that precedes myoblast fusion.     

SMUG1 is able to excise uracil from immunoglobulin genes: insight into mutation versus repair

Mammals harbour multiple enzymes capable of excising uracil from DNA, although their distinct physiological roles remain uncertain. One of them (UNG) plays a critical role in antibody gene diversification, as UNG deficiency alone is sufficient to perturb the process. Here, we show this unique requirement for UNG does not reflect the fact that other glycosylases are unable to access the U:G lesion. SMUG1, if overexpressed, can partially substitute for UNG to assist antibody diversification as judged by its effect on somatic hypermutation patterns (in both DT40 B cells and mice) as well as a restoration of isotype switching in SMUG-transgenic msh2-/- ung-/- mice. However, SMUG1 plays little natural role in antibody diversification because (i) it is diminishingly expressed during B-cell activation and (ii) even if overexpressed, SMUG1 more appears to favour conventional repair of the uracil lesion than assist diversification. The distinction between UNG and overexpressed SMUG1 regarding the balance between antibody diversification and non-mutagenic repair of the U:G lesion could reflect the association of UNG (but not SMUG1) with sites of DNA replication.     

Colonization behaviour of Pseudomonas fluorescens and Sinorhizobium meliloti in the alfalfa (Medicago sativa) rhizosphere

The colonization ability of Pseudomonas fluorescens F113rif in alfalfa rhizosphere and its interactions with the alfalfa microsymbiont Sinorhizobium meliloti EFB1 has been analyzed. Both strains efficiently colonize the alfalfa rhizosphere in gnotobiotic systems and soil microcosms. Colonization dynamics of F113rif on alfalfa were similar to other plant systems previously studied but it is displaced by S. meliloti EFB1, lowering its population by one order of magnitude in co-inoculation experiments. GFP tagged strains used to study the colonization patterns by both strains indicated that P. fluorescens F113rif did not colonize root hairs while S. meliloti EFB1 extensively colonized this niche. Inoculation of F113rif had a deleterious effect on plants grown in gnotobiotic systems, possibly because of the production of HCN and the high populations reached in these systems. This effect was reversed by co-inoculation. Pseudomonas fluorescens F113 derivatives with biocontrol and bioremediation abilities have been developed in recent years. The results obtained support the possibility of using this bacterium in conjunction with alfalfa for biocontrol or rhizoremediation technologies.     

Differential parameters between cytosolic 2‐Cys peroxiredoxins,PRDX1 and PRDX2

Peroxiredoxins are thiol‐dependent peroxidases that function in peroxide detoxification and H₂O₂ induced signaling. Among the six isoforms expressed in humans, PRDX1 and PRDX2 share 97% sequence similarity, 77% sequence identity including the active site, subcellular localization (cytosolic) but they hold different biological functions albeit associated with their peroxidase activity. Using recombinant human PRDX1 and PRDX2, the kinetics of oxidation and hyperoxidation with H₂O₂ and peroxynitrite were followed by intrinsic fluorescence. At pH 7.4, the peroxidatic cysteine of both isoforms reacts nearly tenfold faster with H₂O₂ than with peroxynitrite, and both reactions are orders of magnitude faster than with most protein thiols. For both isoforms, the sulfenic acids formed are in turn oxidized by H₂O₂ with rate constants of ca 2 × 10³ M^?1 s^?1 and by peroxynitrous acid significantly faster. As previously observed, a crucial difference between PRDX1 and PRDX2 is on the resolution step of the catalytic cycle, the rate of disulfide formation (11 s^?1 for PRDX1, 0.2 s^?1 for PRDX2, independent of the oxidant) which correlates with their different sensitivity to hyperoxidation. This kinetic pause opens different pathways on redox signaling for these isoforms. The longer lifetime of PRDX2 sulfenic acid allows it to react with other protein thiols to translate the signal via an intermediate mixed disulfide (involving its peroxidatic cysteine), whereas PRDX1 continues the cycle forming disulfide involving its resolving cysteine to function as a redox relay. In addition, the presence of C83 on PRDX1 imparts a difference on peroxidase activity upon peroxynitrite exposure that needs further study.     

Phylogeny and biogeography of Muusoctopus (Cephalopoda: Enteroctopodidae)

Deep‐sea octopuses of the genus Muusoctopus are thought to have originated in the Pacific Northern Hemisphere and then diversified throughout the Pacific and into the rest of the World Ocean. However, this hypothesis was inferred only from molecular divergence times. Here, the ancestral distribution and dispersal routes are estimated by Bayesian analysis based on a new phylogeny including 38 specimens from the south‐eastern Pacific Ocean. Morphological data and molecular sequences of three mitochondrial genes (16S rRNA, COI and COIII) are presented. The morphological data confirm that specimens newly acquired from off the coast of Chile comprise two species: Muusoctopus longibrachus and the poorly described species, Muusoctopus eicomar. The latter is here redescribed and is clearly distinguished from M. longibrachus and other closely related species in the region. A gene tree was built using Bayesian analysis to infer the phylogenetic position of these species within the species group, revealing that a large genetic distance separates the two sympatric Chilean species. M. longibrachus is confirmed as the sister species of Muusooctopus eureka from the Falkland Islands; while M. eicomar is a sister species of Muusoctopus yaquinae from the North Pacific, most closely related to the amphi‐Atlantic species Muusoctopus januarii. Molecular divergence times and ancestral distribution analyses suggest that genus Muusoctopus may have originated in the North Atlantic: one lineage dispersed directly southward to the Magellan region and another dispersed southward along the Eastern Pacific to the Southern Ocean and Antarctica. The Muusoctopus species in the Southern Hemisphere have different phylogenetic origins and represent independent invasions of this region.