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1. Chromosomes remain individualized through interphase in embryos of the tardigrade Hypsibius exemplaris

   https://doi.org/10.1091/mbc.E25-07-0356  

   Papell, Lillian D; Coke, Adriana N; de_Jesus, Bailey N; Harry, Clayton J; Zhang, Pu; Goldstein, Bob (January 2026, Molecular Biology of the Cell)

   Onishi, Masayuki (Ed.)

   Tardigrades are microscopic animals that can survive exceptional levels of ionizing radiation or desiccation—DNA-damaging conditions that would kill most animals. Irradiation or radiomimetic drug treatment of the tardigrade Hypsibius exemplaris can induce remarkably high expression levels of DNA repair genes, primarily those in the base excision repair and nonhomologous end joining pathways. How tardigrades can repair widespread DNA damage without producing frequent, large-scale chromosome structural abnormalities, like chromosome translocations and fusions, is unknown. Here, we report the results of examining chromosome and nuclear architecture throughout the cell cycle in early embryos of H. exemplaris. We found that H. exemplaris chromosomes are maintained in an individualized form throughout the cell cycle. We were surprised to also find that each chromosome is housed in a fully or partially separate lamin-lined compartment, instead of all chromosomes being housed in a single, nearly spherical nuclear lamina and envelope. Our results reveal unusual chromosomal and nuclear organization in a tardigrade. We speculate that these unexpected features might limit chromosomal rearrangements during DNA damage repair in extreme conditions. 

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2. Animal physiology: How do tardigrades survive intense radiation?

   https://doi.org/10.1016/j.cub.2025.01.057  

   Goldstein, Bob (March 2025, Current Biology)

   Tardigrades survive levels of radiation that would kill most animal life. A new paper unveils more of their tricks, including a pigment that can protect cells from radiation damage and a protein that can concentrate DNA repair machinery at sites of DNA damage. 

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3. A bacterial expression cloning screen reveals single-stranded DNA-binding proteins as potent desicco-protectants

   https://doi.org/10.1016/j.celrep.2024.114956  

   Hibshman, Jonathan D; Clark-Hachtel, Courtney M; Bloom, Kerry S; Goldstein, Bob (November 2024, Cell Reports)

   Desiccation kills most cells. Some proteins have been identified to help certain cells survive desiccation, but many protein protectants are likely to be unknown. Moreover, the mechanisms ensuring protection of key cellular components are incompletely understood. We devised an expression-cloning approach to discover further protectants. We expressed cDNA libraries from two species of tardigrades in E. coli, and we subjected the bacteria to desiccation to select for survivors. Sequencing the populations of surviving bacteria revealed enrichment of mitochondrial single-stranded DNA-binding proteins (mtSSBs) from both tardigrade species. Expression of mtSSBs in bacteria improved desiccation survival as strongly as the best tardigrade protectants known to date. We found that DNA-binding activity of mtSSBs was necessary and sufficient to improve the desiccation tolerance of bacteria. Although tardigrade mtSSBs were among the strongest protectants we found, single-stranded DNA binding proteins in general offered some protection. These results identify single-stranded DNA-binding proteins as potent desicco-protectants. 

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4. Distinct transcriptomic strategies underlie differential heat tolerance in Symbiodiniaceae symbionts

   https://doi.org/10.1093/ismejo/wraf268  

   Xiang, Tingting; Peak, Stephanie L; Huitt, Eric C; Grossman, Arthur R (December 2025, The ISME Journal)

   Abstract Dinoflagellate algae in the family Symbiodiniaceae, symbionts of many marine cnidarians are critical for the metabolic integrity of reef ecosystems, which are increasingly threatened by environmental stress. The resilience of the cnidarian-dinoflagellate symbiosis depends on thermotolerance of the partner organisms; coral hosts that harbor heat-resistant symbionts exhibit greater resistance to bleaching. Although coral responses to heat stress are well-documented, transcriptomic adaptation/acclimation of Symbiodiniaceae to elevated temperatures are limited. Here, we compare thermal responses of two species representing two genera of Symbiodiniaceae, Symbiodinium linucheae (strain SSA01; ITS2 type A4) and Breviolum minutum (strain SSB01; ITS2 type B1). SSA01 in culture maintained photosynthetic function at elevated temperatures and mounted a rapid transcriptomic response characterized by early downregulation of a JMJ21-like histone demethylase coupled with prompt upregulation of transcripts associated with DNA repair and oxidative stress, which would likely contribute to enhanced resilience to heat stress. In contrast, SSB01 experienced a decline in photosynthetic efficiency and a delayed transcriptomic response that included upregulation of transcripts encoding proteasome subunits and reduced transcripts encoding proteins involved in photosynthesis and metabolite transport. These findings indicate that a rapid and moderate transcriptomic response that results in increased expression of genes related to the synthesis and repair of biomolecules might be crucial for thermal tolerance in the Symbiodiniaceae whereas sensitivity to elevated temperatures may be reflected by increased protein turnover and a marked decline in anabolic processes. Understanding these differences is vital for predicting coral responses to warming seas and developing strategies to mitigate heat-stress impacts on reefs. 

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5. Extensive loss of Wnt genes in Tardigrada

   https://doi.org/10.1186/s12862-021-01954-y  

   Chavarria, Raul A.; Game, Mandy; Arbelaez, Briana; Ramnarine, Chloe; Snow, Zachary K.; Smith, Frank W. (December 2021, BMC Ecology and Evolution)

   Abstract Background Wnt genes code for ligands that activate signaling pathways during development in Metazoa. Through the canonical Wnt (cWnt) signaling pathway, these genes regulate important processes in bilaterian development, such as establishing the anteroposterior axis and posterior growth. In Arthropoda, Wnt ligands also regulate segment polarity, and outgrowth and patterning of developing appendages. Arthropods are part of a lineage called Panarthropoda that includes Onychophora and Tardigrada. Previous studies revealed potential roles of Wnt genes in regulating posterior growth, segment polarity, and growth and patterning of legs in Onychophora. Unlike most other panarthropods, tardigrades lack posterior growth, but retain segmentation and appendages. Here, we investigated Wnt genes in tardigrades to gain insight into potential roles that these genes play during development of the highly compact and miniaturized tardigrade body plan. Results We analyzed published genomes for two representatives of Tardigrada, Hypsibius exemplaris and Ramazzottius varieornatus . We identified single orthologs of Wnt4 , Wnt5 , Wnt9 , Wnt11 , and WntA , as well as two Wnt16 paralogs in both tardigrade genomes. We only found a Wnt2 ortholog in H. exemplaris . We could not identify orthologs of Wnt1 , Wnt6 , Wnt7 , Wnt8 , or Wnt10 . We identified most other components of cWnt signaling in both tardigrade genomes. However, we were unable to identify an ortholog of arrow / Lrp5/6 , a gene that codes for a Frizzled co-receptor of Wnt ligands. Additionally, we found that some other animals that have lost several Wnt genes and are secondarily miniaturized, like tardigrades, are also missing an ortholog of arrow / Lrp5/6 . We analyzed the embryonic expression patterns of Wnt genes in H. exemplaris during developmental stages that span the establishment of the AP axis through segmentation and leg development. We detected expression of all Wnt genes in H. exemplaris besides one of the Wnt16 paralogs. During embryo elongation, expression of several Wnt genes was restricted to the posterior pole or a region between the anterior and posterior poles. Wnt genes were expressed in distinct patterns during segmentation and development of legs in H. exemplaris , rather than in broadly overlapping patterns. Conclusions Our results indicate that Wnt signaling has been highly modified in Tardigrada. While most components of cWnt signaling are conserved in tardigrades, we conclude that tardigrades have lost Wnt1 , Wnt6 , Wnt7 , Wnt8 , and Wnt10 , along with arrow / Lrp5/6 . Our expression data may indicate a conserved role of Wnt genes in specifying posterior identities during establishment of the AP axis. However, the loss of several Wnt genes and the distinct expression patterns of Wnt genes during segmentation and leg development may indicate that combinatorial interactions among Wnt genes are less important during tardigrade development compared to many other animals. Based on our results, and comparisons to previous studies, we speculate that the loss of several Wnt genes in Tardigrada may be related to a reduced number of cells and simplified development that accompanied miniaturization and anatomical simplification in this lineage. 

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