Articles publicats en revistes (Institut de Recerca de la Biodiversitat (IRBio))

Background

Several intercellular signalling pathways (including wingless (Wnt), hedgehog (Hh), and bone morphogenetic protein (BMP)) are used repeatedly in animals throughout development and evolution and are also frequent targets for disease-associated disruptions. We have previously shown that the major transcriptional effectors of β-catenin-dependent Wnt signalling, the TCF/LEF proteins, in contrast to other pathway components, have a higher gene number and isoform diversity in vertebrates versus invertebrates, but this increased diversity has only been poorly quantified. Considering that isoform diversity correlates with organism complexity, any increase in major signalling effectors is likely to have made a significant contribution to vertebrate evolution.

Results

Using de novo long-read transcriptomes, we compared isoform number per gene for the chordates Ciona intestinalis, Lampetra planeri and Xenopus tropicalis, thus encompassing the invertebrate sister group to vertebrates, as well as a cyclostome and a gnathostome vertebrate. We find a significant increase in the number of transcript isoforms per gene expressed during embryo development and organogenesis at the invertebrate-to-vertebrate transition, specifically for the main transcription factor effectors of the Wnt/β-catenin, Hh and BMP pathways, i.e. TCF/LEF, GLI and SMAD.

Conclusions

Our results implicate an increase in isoform diversity of the transcription factors of major intercellular signalling pathways as having a disproportionate role in the evolutionary origin and diversification of vertebrates.

Marine ectotherms, organisms whose body temperature depends on their environment, often rely on physiological plasticity

to withstand rapid temperature increases when behavioural adjustments are insufficient. Despite extensive research

on thermal tolerance, gaps remain in understanding species- and population-level metabolic responses to acute thermal

stress, particularly in rapidly warming regions like the Mediterranean Sea. This study assessed metabolic responses to

acute warming in four echinoderm species with distinct thermal affinities but overlapping distributions in the Western

Mediterranean: the sea urchins Arbacia lixula (subtropical) and Paracentrotus lividus (temperate-cold), and the brittle

stars Ophiothrix sp. II (temperate) and Ophiocomina nigra (temperate-cold). Oxygen consumption, used as a proxy for

Basal Metabolic Rate (BMR), was measured at sequential temperatures (16 °C, 20 °C, 23 °C, 26 °C), following a short

acclimation period. Species exhibited divergent metabolic trajectories and thermal sensitivities (Q₁₀), reflecting their thermal

affinities, local adaptations, and phenotypic plasticity. A. lixula and Ophiothrix sp. II displayed sharp BMR increases,

indicating resilience but proximity to their upper thermal limits. In contrast, O. nigra maintained stable metabolic rates,

suggesting broad physiological plasticity. P. lividus displayed population-level divergence: individuals with cooler-origin

experienced metabolic suppression and severe thermal stress at 26 °C, whereas those with warmer-origin maintained

higher metabolic activity. Overall, phenotypic plasticity emerged as a key short-term strategy to cope with acute warming.

However, species with narrower thermal tolerance, such as P. lividus, might face long-term vulnerability under intensifying

marine heatwaves. These results highlight the importance of integrating thermal history, plasticity, and genetic variation

to accurately predict resilience to ocean warming.