Biology subjects

Gahan, J.

Publications and source records attributed to Gahan, J..

4 recordsLinked to original sources

bioRxiv2023

The genome of the colonial hydroid Hydractinia reveals their stem cells use a toolkit of genes shared with all animals

Hydractinia is a colonial marine hydroid that exhibits remarkable biological properties, including the capacity to regenerate its entire body throughout its lifetime, a process made possible by its adult migratory stem cells, known as i-cells. Here, we provide an in-depth characterization of the genomic structure and gene content of two Hydractinia species, H. symbiolongicarpus and H. echinata, placing them in a comparative evolutionary framework with other cnidarian genomes. We also generated and annotated a single-cell transcriptomic atlas for adult male H. symbiolongicarpus and identified cell type markers for all major cell types, including key i-cell markers. Orthology analyses based on the markers revealed that Hydractinias i-cells are highly enriched in genes that are widely shared amongst animals, a striking finding given that Hydractinia has a higher proportion of phylum-specific genes than any of the other 41 animals in our orthology analysis. These results indicate that Hydractinias stem cells and early progenitor cells may use a toolkit shared with all animals, making it a promising model organism for future exploration of stem cell biology and regenerative medicine. The genomic and transcriptomic resources for Hydractinia presented here will enable further studies of their regenerative capacity, colonial morphology, and ability to distinguish self from non-self.

genomics↗

bioRxiv2022

A cellular and molecular analysis of SoxB-driven neurogenesis in a cnidarian

Neurogenesis is the generation of neurons from stem cells, a process that is regulated by SoxB transcription factors (TFs) in many animals. Although the roles of these TFs are well understood in bilaterians, how their neural function evolved is unclear. Here, we use Hydractinia symbiolongicarpus, a member of the early-branching phylum Cnidaria, to provide insight into this question. Using a combination of mRNA in situ hybridization, transgenesis, gene knockdown, transcriptomics, and in-vivo imaging, we provide a comprehensive molecular and cellular analysis of neurogenesis during embryogenesis, homeostasis, and regeneration in this animal. We show that SoxB genes act sequentially. Stem cells expressing Piwi1 and Soxb1, which have a broad developmental potential, become neural progenitors that express Soxb2 before differentiating into mature neural cells. Knockdown of SoxB genes resulted in complex defects in embryonic neurogenesis. Hydractinia neural cells differentiate while migrating from the aboral to the oral end of the animal, but it is unclear whether migration per se or exposure to different microenvironments is the main driver of their fate determination. Our data constitute a rich resource for studies aiming at addressing this question, which is at the heart of understanding neurological disorders in all animals, including humans.

developmental biology↗

bioRxiv2021

Linking plant growth promoting arbuscular mycorrhizal colonization with bacterial plant sulfur supply

Sulfur (S) exists in organically bound complexes ([~]95%), predominantly as sulfonates, and are not directly plant available. Specific soil bacteria can mobilise sulfonates but very little is known about these bacteria in the hyphosphere. Since mycorrhizal fungi support growth of the majority of land plants, hyphosphere desulfonating bacteria may be of substantial benefit to the plant host. This study analysed the effect of AM inoculation with Rhizophagus irregularis (former G. intraradices, Glomus) and a mix of six AM species (Mixed) on PGP, microbial communities and sulfonate mobilising bacteria with L. perenne, Agrostis stolonifera and Plantago lanceolata as plant hosts in bi-compartmental microcosms and A. stolonifera in PGP pot experiments. AM inoculation significantly increased plant growth, percentage root colonisation and the quantity of cultivable desulfonating bacteria in the hyphosphere over pre-inoculated soil for all plants. Community analysis via PCR-DGGE revealed significantly different bacterial and fungal communities post inoculation. Analysis of the sulfonate mobilising asfA gene revealed a significantly altered community and novel bacterial isolates with this important functional ability post-inoculation. The results demonstrate that AM inoculation increased plant biomass yield, AM root colonisation and altered bacterial and fungal community dynamics in the hyphosphere. AM inoculated microcosms had an increased abundance of desulfonating bacteria that may be beneficial for plant-S supply. Research highlightsO_LIInoculation with AM fungi was shown to promote plant growth and harbour larger populations of sulfonate mobilising bacteria. C_LIO_LIPost-inoculation hyphospheric bacterial and saprotrophic fungal communities were shown to differ significantly in composition and abundance. C_LIO_LIAnalysis of sulfonate mobilising bacteria revealed novel presumptive species in possession of the asfA gene associated with AM hyphae. C_LIO_LIAM inoculation was shown to significantly impact the asfA positive bacterial community composition. C_LI

microbiology↗

bioRxiv2021

The role of arbuscular mycorrhiza and organosulfur mobilizing bacteria in plant sulphur supply

AM fungi are enhancing growth and health of many land plants but only some of these beneficial mechanisms are well understood. This study aimed to uncover the role of bacteria colonising AM fungi in organically-bound sulfur (S) mobilisation, the dominant S pools in soil that are not directly available to plants. The effect of an intact AM symbiosis with access to stable isotope organo-34S enriched soils encased in 35 {micro}m mesh cores was tested in microcosms with Agrostis stolonifera and Plantago lanceolata. At 3 month intervals, the plant shoots were analysed for 34S uptake. After 9 months, hyphae and associated soil was picked from static (mycorrhizal) and rotating (severed hyphae) mesh cores and corresponding rhizosphere soil was sampled for bacterial analysis. AM symbiosis increased uptake of 34S from organo-34S enriched soil at early stages of plant growth when S demand appeared to be high. The static (mycorrhizal) treatments were shown to harbour larger populations of cultivable heterotrophs and sulfonate mobilising bacteria. Microbial communities were significantly different in the hyphosphere of mycorrhizal hyphae and hyphae not associated to plant hosts. Sulfate ester (arylsulfatase enzyme assay, atsA gene) and sulfonate mobilising activity (asfA gene) was altered by an intact AM symbiotic partnership which stimulated the genera Azospirillum, Burkholderia and Polaromonas. Illumina sequencing revealed that AM symbiosis led to community shifts, reduced diversity and dominance of the Planctomycetes and Proteobacteria. This study demonstrated that AM symbioses can promote organo-S mobilization and plant uptake through interaction with hyphospheric bacteria. Research highlightsO_LIAM hyphae enhanced uptake of organically bound 34S at early stages of growth. C_LIO_LIAM hyphosphere harboured a large population of organo-S desulfurizing bacteria. C_LIO_LIMicrobial communities significantly differed in rotating and static mesh cores. C_LIO_LIAM hyphae influenced bacterial sulfate ester and sulfonate mobilising activity. C_LIO_LIAM hyphae reduced bacterial diversity, increased Planctomycetes and Proteobacteria abundance. C_LI

microbiology↗