Photosynthetic response to a winter heatwave in leading and trailing edge populations of the intertidal red alga Corallina offi-cinalis(Rhodophyta)

Marine heatwaves(MHWs)caused by anthropogenic climate change are becoming a key driver of change at the ecosystem level.Thermal conditions experienced by marine organisms across their distribution,particularly towards the equator,are likely to approach their physiological limits,resulting in extensive mortality and subsequent changes at the population level.Populations at the margins of their species’distribution are thought to be more sensitive to climate-induced environmental pressures than central populations,but our understanding of variability in fitness-related physiological traits in trailing versus leading-edge populations is limited.In a laboratory simulation study,we tested whether two leading(Iceland)and two trailing(Spain)peripheral populations of the intertidal macroalga Corallina officinalis display different levels of maximum potential quantum efficiency(Fv/Fm)resilience to current and future winter MHWs scenarios.Our study revealed that ongoing and future local winter MHWs will not negatively affect leading-edge populations of C.officinalis,which exhibited stable photosynthetic efficiency throughout the study.Trailing edge populations showed a positive though non-significant trend in photosynthetic efficiency throughout winter MHWs exposure.Poleward and equatorward populations did not produce significantly different results,with winter MHWs having no negative affect on Fv/Fm of either population.Additionally,we found no long-term regional or population-level influence of a winter MHWs on this species’photosynthetic efficiency.Thus,we found no statistically significant difference in thermal stress responses between leading and trailing populations.Nonetheless,C.officinalis showed a trend towards higher stress responses in southern than northern populations.Because responses rest on a variety of local population traits,they are difficult to predict based solely on thermal pressures.

Isolation and characterisation of human gingival margin-derived STRO-1/MACS^+ and MACS^-cell populations

Recently,gingival margin-derived stem/progenitor cells isolated via STRO-1/magnetic activated cell sorting（MACS） showed remarkable periodontal regenerative potential in vivo.As a second-stage investigation,the present study＇s aim was to perform in vitro characterisation and comparison of the stem/progenitor cell characteristics of sorted STRO-1-positive（MACS~＋） and STRO-1-negative（MACS^-） cell populations from the human free gingival margin.Cells were isolated from the free gingiva using a minimally invasive technique and were magnetically sorted using anti-STRO-1 antibodies.Subsequently,the MACS~＋ and MACS^- cell fractions were characterized by flow cytometry for expression of CD14,CD34,CD45,CD73,CD90,CD105,CD146/MUC18 and STRO-1.Colony-forming unit（CFU） and multilineage differentiation potential were assayed for both cell fractions.Mineralisation marker expression was examined using real-time polymerase chain reaction（PCR）.MACS~＋ and MACS- cell fractions showed plastic adherence.MACS~＋ cells,in contrast to MACS- cells,showed all of the predefined mesenchymal stem/progenitor cell characteristics and a significantly higher number of CFUs（P〈0.01）.More than 95%of MACS~＋ cells expressed CD105,CD90 and CD73;lacked the haematopoietic markers CD45,CD34 and CD14,and expressed STRO-1 and CD146/MUC18.MACS- cells showed a different surface marker expression profile,with almost no expression of CD14 or STRO-1,and more than 95%of these cells expressed CD73,CD90 and CD146/MUC18,as well as the haematopoietic markers CD34 and CD45 and CD105.MACS~＋ cells could be differentiated along osteoblastic,adipocytic and chondroblastic lineages.In contrast,MACS- cells demonstrated slight osteogenic potential.Unstimulated MACS~＋ cells showed significantly higher expression of collagen I（P〈0.05） and collagen III（P〈0.01）,whereas MACS^- cells demonstrated higher expression of osteonectin（P〈0.05;MannWhitney）.The present study is the first to compare gingival MACS~＋ and MACS- cell populations demonstrating that MACS~＋ cells,in contrast to MACS- cells,harbour stem/progenitor cell characteristics.This study also validates the effectiveness of the STRO-l/MACS~＋technique for the isolation of gingival stem/progenitor cells.Human free gingival margin-derived STRO-1/MACS~＋ cells are a unique renewable source of multipotent stem/progenitor cells.