The neuropeptide Pth2 modulates social behavior and anxiety in zebrafish

Animal behavior is strongly context-dependent and behavioral performance is often modulated by internal state. In particular, different social contexts can alter anxiety levels and modulate social behavior. The vertebrate-specific neuropeptide parathyroid hormone 2 (pth2) is directly regulated by the presence or absence of conspecifics in zebrafish. As its cognate receptor, the parathyroid hormone 2 receptor (pth2r), is widely expressed across the brain, we tested fish lacking the functional Pth2 peptide in several anxiety-related and social paradigms. Rodents lacking PTH2 display increased anxiety-related behavior. Here we show that the propensity to react to sudden stimuli with an escape response is increased in pth2-/- zebrafish, consistent with elevated anxiety. While overall social preference for conspecifics is maintained in pth2-/- fish until the early juvenile stage, we found that both social preference and shoaling are altered later in development. The data presented suggest that the neuropeptide Pth2 modulates several conserved behavioral features, and may thus enable the animal to react appropriately in different social contexts.

Ontogeny of Orientation during the Early Life History of the Pelagic Teleost Mahi-Mahi, Coryphaena hippurus Linnaeus, 1758

Understanding the orientation behavior and capabilities in early life history (ELH) of fishes is critical for studying their dispersal but has, surprisingly, never been tested in any pelagic species. We here investigate the ontogeny of orientation and swimming abilities of the pelagic Coryphaena hippurus Linnaeus, 1758 larvae, hereafter mahi-mahi, through their ELH stages using the Drifting In Situ Chamber (DISC) in a laboratory setup. The DISC was deployed in a large (3 m3) circular aquarium in order to control the stimulus perceived by the fish and to identify behavioral response at the individual, developmental stage, and population levels. A total of 79 individual ranging from 7 to 23 days post hatch and from preflexion to early juvenile stages were exposed to a directional light mimicking the sun’s position. Orientation towards the light direction was tested by switching the light by 180° among trials. To compare the orientation among development stages, we scaled the directionality by the swimming ability, therein defined as “directionality competence”. The results show that while mahi-mahi directionality competence increases through ontogeny, they acquire a positive and directional phototaxis behavior at the flexion stage. This potential solar orientation is kept through the early juvenile stage. Mahi-mahi may thus be able to use the sun as a compass in the open ocean as observed in the larval stages of demersal species seeking for settlement habitats. This ability notably develops before the improvement of their swimming capabilities, suggesting that early orientation—even at micro-scale—and swimming capabilities may be equally important for the survival of the ELH stages of pelagic species.

Transcriptome analysis of growth variation in early juvenile stage sandfish Holothuria scabra

The sandfish Holothuria scabra is a high-value tropical sea cucumber species representing a major mariculture prospect across the Indo-Pacific. Advancements in culture technology, rearing, and processing present options for augmenting capture production, stock restoration, and sustainable livelihood activities from hatchery-produced sandfish. Further improvements in mariculture production may be gained from the application of genomic technologies to improve performance traits such as growth. In this study, we performed de novo transcriptome assembly and characterization of fast- and slow-growing juvenile H. scabra from three Philippine populations. Analyses revealed 66 unigenes that were consistently differentially regulated in fast-growing sandfish and found to be associated with immune response and metabolism. Further, we identified microsatellite and single nucleotide polymorphism markers potentially associated with fast growth. These findings provide insight on potential genomic determinants underlying growth regulation in early juvenile sandfish which will be useful for further functional studies.HighlightsThe study explores the genomic basis of growth variation in juvenile sandfish by examining gene expression profiles of fast- and slow-growing early juvenile stages from three hatchery populations using RNA-seq.Sixty-six differentially regulated unigenes potentially related to growth variation are associated with several biological and molecular processes, including carbohydrate binding, extracellular matrix organization, fatty-acid metabolism, and metabolite and solute transport.A large number of potential microsatellite and growth category-associated SNP markers have been identified.

Expression of Human SBDSR126T in Sbds Null Background Shows Eif6 Dysregulation: An Adult Zebrafish Model for Shwachman-Diamond Syndrome

Background. Shwachman-Diamond Syndrome (SDS) is an autosomal recessive disorder characterized by pancreatic insufficiency, skeletal defects, neutropenia, and an increased risk of myelodysplastic syndrome (MDS)/acute myeloid leukemia (AML). SDS occurs in 1/75,000 births, and biallelic mutations in the SBDS gene account for ~90% of patients. The SBDS protein is highly conserved. SBDS interacts physically with EFL1 to release EIF6 from the cytoplasmic pre-60S ribosomal subunit and promote the assembly of the mature 80S ribosome. The SBDS R126T allele is found in combination with the common K62X mutation in some SDS patient. A recent study showed that the SBDSR126T is not able to activate the GTPase activity of the EFL1, affecting the release of EIF6 from the 60S surface. Methods. We created a zebrafish knockout line that phenocopies the SDS with neutropenia, pancreas atrophy, small size (Figure 1A), and decreased 80S ribosomes. To rescue those fish from early mortality, we generated a new transgenic line Tg(ubi:SBDSR126T:pA) expressing the missense variant R126T, a disease-associated allele. Results. The sbds knockout fish die after 21 days post fertilization (dpf), corresponding to an early juvenile stage. However, the SBDSR126T transgenic line in the background of the sbds knockout can live for at least 12 months. This is in strong contrast to the mouse SbdsR126T/R126T line that do not survive to birth. Transgenically-rescued fish displayed a small size phenotype resembling SDS (Figure 1B). Levels of ribosomal proteins Rpl5 and Rpl11 were lower in the sbds knockout at 21 dpf but they were normal in the transgenic line at 6 months. We also observed a concordant regulation of Sbds and Eif6 expression (Figure 1C,D). sbds null fish showed a significant upregulation of cdkn1a, while in their transgenic siblings levels were normal (Figure 1E). Moreover, mpx was upregulated in the transgenic line with the null background (Figure 1F). Analysis of neutrophil and monocyte counts are being performed and will be reported. Conclusions. Our novel SBDSR126T zebrafish model survives until adulthood, which will allow us to carry out a number of informative assays such as stress response, gene expression, and polysome profiles in different organs. Rpl5 and Rpl11 levels are affected in sbds mutants but not in the transgenic line. Activation of cdkn1a (p21) in sbds mutants might lead to apoptosis and death. The normal levels of cdkn1a in the transgenic line might be non-deleterious, as loss of Tp53 activation can rescue some models of bone marrow failure. In addition, loss of sbds or expression of SBDSR126T affect Eif6 levels in zebrafish. Importantly, some patients with SBDS deficiency acquire interstitial deletions of chromosome 20, resulting in the loss of the EIF6 gene. This might be a potential mechanism to suppress the defect in ribosome biogenesis by reducing the copy number of the EIF6 gene and has been related to a lower risk of MDS/AML comparing to other SDS patients. Our adult model of Shwachman-Diamond Syndrome can provide new insights into the pathogenesis of SDS and its progression to malignancy, which can be used to identify novel targets for AML/MDS therapy. Figure 1 Disclosures No relevant conflicts of interest to declare.

Small-scale distribution patterns of two cirratulid species with a description of a peculiar early juvenile stage

An assemblage of cirratulids in a confined marine basin (Mediterranean Sea) was investigated at small spatio-temporal scales in an experiment in which artificial granules of expanded fire-clay were used as a bare substratum for colonization. Analysis of core samples of 3.5 l undisturbed natural sediments (source area) and equal volumes of artificial substratum (new settlement area), plunged into the sea bottom were carried out from May to July 2008 after 0, 15, 30 and 60 days.Caulleriella bioculatashowed the highest total mean density of 10.1 ± 5.8 N l−1in the natural sediment, and the lowest at 0.13 ± 0.08 N l−1in the artificial substratum, with a marked temporal decrease. Individuals were not strongly aggregated and were found in a deeper sediment layer. The density of largeCirriformia tentaculatawas 0.5 ± 0.3 N l−1, with individuals more aggregated and confined to shallower sediments, versus 0.10 ± 0.06 N l−1but found deeper in the artificial substratum; temporal trends were not straightforward for this species. The adult stage of sedentary cirratulids appeared to actively move into the new available substratum from the neighbouring sediments. An early cirratulid juvenile stage was observed in both microhabitats at a comparable density of 1.8 ± 2.8 N l−1with highly aggregated individuals (cohorts). The peculiar morphology of branchiae, the threadlike body shape and the multivariate morphological differences between two sub-populations settled in the different substrata are reported for these problematic specimens.