Biology subjects

Johnston, E. C.

Publications and source records attributed to Johnston, E. C..

4 recordsLinked to original sources

bioRxiv2025

Positive associations between growth and thermal tolerance in the reef-building coral Montipora capitata

Relationships between ecologically important traits are increasingly important for the future of coral reefs, which are declining globally due to a variety of stressors. Corals that resist and recover from bleaching will be selected under future climates, which may negatively or positively impact a range of associated traits important for the structure and function of contemporary and future reefs. Using standardized assays, we investigated growth under ambient conditions, bleaching resistance and recovery after bleaching in a model population of 60 Montipora capitata colonies harboring diverse symbiont communities. We found significantly higher trait variance within Durusdinium-dominated colonies, highlighting the interaction of host and symbiont. We also show that symbiont community impacted thermal tolerance and survivorship during the thermal stress assay, but not recovery or growth. There was also a positive relationship between thermal tolerance and change in surface area and thermal tolerance and recovery from equivalent amounts of stress. These results demonstrate limited tradeoffs to thermal tolerance and suggest that bleaching tolerant corals in this model system are suited to recover from stress and maintain high growth rates under ambient conditions, providing insight into the adaptive capacity of thermally tolerant corals in the Anthropocene.

ecology↗

bioRxiv2024

Stepwise recruitment of Hsc70 by DNAJB1 produces ordered arrays primed for bursts of amyloid fibre disassembly

To understand the action of co-chaperones of the J-domain protein family in the assembly of disaggregation-active Hsc70 complexes on the surface of amyloid fibres, we used cryo-EM and tomography to compare the assemblies with wild-type co-chaperones or an activity deficient mutant. We show that human DNAJB1 binds uniformly and densely along -synuclein amyloid fibres in an asymmetric orientation, with one subunit of the DNAJB1 dimer lying along the fibre surface and the other subunit further away. It acts in a 2-step recruitment of Hsc70 to the fibres, first releasing DNAJB1 auto-inhibition and then activating the Hsc70 ATPase by the J domain, with ATPase recycling stimulated by the nucleotide exchange factor Apg2. When the auto-inhibition is removed by mutating the H5 inhibitory binding site on DNAJB1 ({Delta}1H5 DNAJB1 mutant), Hsc70 is recruited to the fibres at a normal level, but the resulting complex is inactive in disaggregation. Cryo tomography of the wild-type DNAJB1:Hsc70:Apg2:Syn fibre complex shows dense arrays of the chaperones extending out from the fibre surface along spiral tracks, with the Hsc70 density on the outer surface of the DNAJB1 layer. The {Delta}1H5 DNAJB1:Hsc70:Apg2:Syn fibre complex results in equally dense but less organised binding all over the fibre surface and lacks the ordered clusters. On the basis of these findings, we propose that 2-step activation of DNAJB1 regulates Hsc70 access to the fibre substrate. Since the DNAJB1 dimers are bound every 40 [A], the J domain released by Hsc70 binding to one dimer could activate the ATPase of an Hsc70 bound to the adjacent dimer. This could trigger a cascade of recruitment and activation in a localised, dense cloud of Hsc70 molecules to give coordinated, sequential binding and disaggregation from an exposed fibre end, as observed by cryo-EM and earlier fluorescence and AFM studies.

biochemistry↗

bioRxiv2022

Cophylogeny and specificity between cryptic coral species (Pocillopora spp.) at Moorea and their symbionts (Symbiodiniaceae)

The congruence between phylogenies of tightly associated groups of organisms (cophylogeny) reflects evolutionary links between ecologically important interactions. However, despite being a classic example of an obligate symbiosis, tests of cophylogeny between scleractinian corals and their photosynthetic algal symbionts have been hampered in the past because both corals and algae contain genetically unresolved and morphologically cryptic species. Here, we studied co-occurring, cryptic Pocillopora species from Moorea, French Polynesia, that differ in their relative abundance across depth. We constructed new phylogenies of the host Pocillopora (using genomic loci, complete mitochondrial genomes, and thousands of single nucleotide polymorphisms) and their Symbiodiniaceae symbionts (using ITS2 and psbAncr markers) and tested for cophylogeny. The analysis supported the presence of five Pocillopora species on the fore-reef at Moorea that mostly hosted either Cladocopium latusorum or C. pacificum. Only Pocillopora species hosting C. latusorum, and that have similar relative abundances across depths, also hosted taxa from Symbiodinium and Durusdinium. In general, the Cladocopium phylogeny mirrored the Pocillopora phylogeny. Within Cladocopium species, lineages also differed in their associations with Pocillopora haplotypes, except those showing evidence of nuclear introgression, and with depth in the two most common Pocillopora species. We also found evidence for a new Pocillopora species (haplotype 10), that has so far only been sampled from French Polynesia, that warrants formal identification. The linked phylogenies of these Pocillopora and Cladocopium species and lineages suggest that symbiont speciation is driven by niche diversification in the host, but there is still evidence for symbiont flexibility in rare cases.

evolutionary biology↗

bioRxiv2021

Cooperative Amyloid Fibre Binding and Disassembly by the Hsp70 disaggregase

Although amyloid fibres are highly stable protein aggregates, a specific combination of human Hsp70 system chaperones can disassemble them, including fibres formed of -synuclein, huntingtin or Tau. Disaggregation requires the ATPase activity of the constitutively expressed Hsp70, Hsc70, together with the J domain protein DNAJB1 and the nucleotide exchange factor Apg2. Recruitment and clustering of Hsc70 on the fibrils appear to be necessary for disassembly. Here we use atomic force microscopy (AFM) to show that segments of in vitro assembled -synuclein fibrils are first coated with chaperones and then undergo bursts of rapid, unidirectional disassembly. Cryo-electron tomography reveals fibrils with regions of densely bound chaperones extending from the fibre surface, preferentially at one end of the fibre. Sub-stoichiometric amounts of Apg2 relative to Hsc70 dramatically increase recruitment of Hsc70 to the fibres, creating localised active zones that then undergo rapid disassembly at a rate of [~]4 subunits per second.

biochemistry↗