Biology subjects

Johannesen, A.

Publications and source records attributed to Johannesen, A..

4 recordsLinked to original sources

bioRxiv2026

EFN-4/Ephrin converges with SAX-3/Robo, UNC-6/Netrin, and Heparan Sulfate Proteoglycan signaling to control MAB-5/Hox-dependent posterior Q neuroblast migration in Caenorhabditis elegans

Hox genes have been broadly implicated in nervous system development, but the molecular and genetic mechanisms that act downstream of Hox factors remain to be identified. The MAB-5 antennapedia-like Hox transcription factor is both necessary and sufficient to cause posterior migration of the Q neuroblast descendants in Caenorhabditis elegans. In response to MAB-5, the left-side QL descendants QL.a and QL.ap undergo a three-stage migration process, with each stage characterized by a posterior lamellipodial protrusion followed by cell body migration. The QL.ap cell differentiates into the PQR neuron posterior to the anus. Previous studies showed that the MAB-5-regulated gene efn-4/Ephrin was required for the third and final stage of QL.ap migration, with efn-4 mutation resulting in placement of PQR immediately anterior to the anus. This subtle and previously-undescribed phenotype opens the possibility that other known neuronal development genes could be involved. In this work, we screened known signaling mutants for third-stage PQR migration defects. We found that mutations in SAX-3/Robo signaling, UNC-6/Netrin signaling, and heparan sulfate proteoglycans (HSPGs) all displayed third-stage PQR migration defects. The effects in single mutants were weak compared to efn-4, and double mutant analysis revealed lack of genetic synergy, consistent with all of these molecules converging on a common pathway. This genetic analysis is consistent with physical interaction studies in vitro from another group that suggest that these molecules form connected communities of interacting extracellular domains, raising the possibility that they are all components of a large extracellular signaling complex required for posterior QL.ap migration. In this model, we envision that MAB-5/Hox drives EFN-4/Ephrin expression in QL.ap, which then seeds the formation of an extracellular signaling complex containing SAX-3/Robo signaling, UNC-6/Netrin signaling, and HSPGs that drives posterior lamellipodial formation and posterior migration.

developmental biology↗

bioRxiv2025

Effect of plastic and seaweed shelters on the skin microbiome of lumpfish Cyclopterus lumpus used as cleaner fish in aquaculture pens

Atlantic salmon (Salmo salar) aquaculture is a major industry in several countries worldwide and a growing enterprise in others. One of the main challenges the industry faces is infestations with the parasitic copepod Lepeoptheirus salmonis, or salmon lice. Several different chemical and mechanical methods are available for alleviating the problem, but often at cost to salmon welfare and/or the environment. In some regions cleaner fish have been introduced to farming facilities as an environmentally and salmon welfare friendly option for reducing the sea lice infestations. In some North Atlantic countries, lumpfish (Cyclopterus lumpus) are being used as cleaner fish. However, the welfare and high mortality rates of lumpfish in salmon farming is frequently a problem, and the need to improve lumpfish welfare is great. One adaptation for salmon farms is to provide the lumpfish with shelters to meet their need to rest and hide. Plastic shelters are the most widely used form, but seaweed shelters have more recently also been applied as a more natural solution. This project investigated the potential effect of seaweed and plastic shelters on the skin and gill microbiome of lumpfish and any potential correlation to their welfare. In an experimental setup in a commercial salmon farming facility, lumpfish from pens with either plastic or seaweed shelters were sampled over a period of approximatly three months. The results showed that the bacterial communities on the two shelter types were significantly different and fewer potentially pathogenic bacteria dominated the skin microbiota of lumpfish living with seaweed shelters than of those living with plastic shelters. No differences were detected in the welfare of the lumpfish and further investigations are needed to clarify any potential implications of the differences detected in the skin microbiota of lumpfish including responses to stressful conditions.

molecular biology↗

bioRxiv2024

The digestion time for salmon louse (Lepeoptheirus salmonis) in lumpfish (Cyclopterus lumpus) in relation to freshness, developmental stage, and temperature

Sea lice infestations cause significant economic losses in the Atlantic salmon aquaculture industry. To biologically control sea lice at farming sites, cleaner fish such as lumpfish are employed. However, the efficacy of lumpfish is under constant debate, primarily due to limited knowledge of digestion times, which makes it difficult to interpret the number of salmon lice found in the stomach contents of dissected lumpfish. The aim of this study was to provide quantitative estimates of the degradation of salmon lice over a period of 12 days. After an acclimation period of approximately one week, batches of eight lumpfish (average weight 94.3 g, SD {+/-} 33.2) were fed salmon lice and arranged in tanks. Each batch received six large mobile lice and two adult female lice. Samplings were conducted at 24-hour intervals during the first four days and at 48-hour intervals over the remaining eight days. The experiment was conducted twice, each at a different temperature regime (6{degrees}C and 9{degrees}C), using live lice in both trials. To investigate if the freshness of the louse influenced degradation and digestion, the setup was replicated in the 9{degrees}C experiment with lice that had been stored frozen at -80{degrees}C, with an additional 12-hour sampling point for comprehensive observation. The analysis of salmon lice revealed expected digestion times of 6.8 days and 12 days for large mobile and adult female salmon lice, respectively. Temperature and lice freshness did not seem to influence digestion times, but the developmental stage of the lice did. The findings of this study can be used to estimate the cleaning efficacy of lumpfish based on the stomach contents.

ecology↗

bioRxiv2021

Waves and currents decrease the available space in a salmon cage

Due to increasing demand for salmon and environmental barriers preventing expansion in established sites, salmon farmers seek to move or expand their production to more exposed sites. In this study we investigate the effects of strong currents and waves on the behaviour of salmon and how they choose to use the space available to them. Observations are carried out in a site with strong tidal currents and well mixed water. Using video cameras and echo sounders, we show that salmon prefer to use the entire water column, narrowing their range only as a response to cage deformation, waves, or daylight. Conversely, salmon show strong horizontal preference, mostly occupying the portions of the cage exposed to currents. Additionally, waves cause salmon to disperse from the exposed side of the cage to the more sheltered side. Even when strong currents decrease the amount of available space, salmon choose to occupy the more exposed part of the cage. This indicates that at least with good water exchange, the high density caused by limited vertical space is not so aversive that salmon choose to move to less desirable areas of the cage. However, the dispersal throughout the entire available water column indicates that ensuring enough vertical space, even in strong currents, would be beneficial to salmon welfare.

animal behavior and cognition↗