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ABSTRACT Cave‐dwelling animals thrive in isolated caves despite the pressures of darkness, starvation, and reduced oxygen. Prior work revealed thatAstyanaxcave‐dwelling morphs derived from different cave localities express significantly higher levels of blood hemoglobin compared to surface‐dwelling fish. Interestingly, this elevation is maintained in different populations of cavefish, despite captive rearing in normal oxygen conditions. We capitalized on the consistent response of elevated hemoglobin in captive cavefish, which were derived from geographically distinct regions, to determine if this elevation is underpinned by expression of the sameHbgenes. Blood hemoglobin proteins are encoded by a large family ofhemoglobin(Hb) gene family members, which demonstrate coordinated expression patterns, subject to various organismal (e.g., period of life history) and environmental influences (e.g., oxygen availability). Surprisingly, we found that geographically distinct populations showed mostly divergent patterns ofHbgene expression. Cavefish from two cave localities, Pachón and Tinaja, have a more recent shared origin, and show more similarHbexpression patterns as adults. However, during embryonic phases, Pachón and Tinaja show significant variability in timing of peak expression ofHbfamily members. In sum, the transcriptomic underpinnings ofHbgene expression represents a complex composite of shared and divergent expression patterns across three captive cavefish populations. We conclude that these differential patterns are likely influenced by life history, and the unique cave conditions in which these animals evolved.
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This content will become publicly available on December 12, 2025
Bicoid-nucleosome competition sets a concentration threshold for transcription constrained by genome replication
SUMMARY Transcription factors (TFs) regulate gene expression despite constraints from chromatin structure and the cell cycle. Here we examine the concentration-dependent regulation ofhunchbackby the Bicoid morphogen through a combination of quantitative imaging, mathematical modeling and epigenomics inDrosophilaembryos. By live imaging of MS2 reporters, we find that, following mitosis, the timing of transcriptional activation driven by thehunchbackP2 (hbP2) enhancer directly reflects Bicoid concentration. We build a stochastic model that can explainin vivoonset time distributions by accounting for both the competition between Bicoid and nucleosomes athbP2 and a negative influence of DNA replication on transcriptional elongation. Experimental modulation of nucleosome stability alters onset time distributions and the posterior boundary ofhunchbackexpression. We conclude that TF-nucleosome competition is the molecular mechanism whereby the Bicoid morphogen gradient specifies the posterior boundary ofhunchbackexpression.
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- Award ID(s):
- 2235451
- PAR ID:
- 10611993
- Publisher / Repository:
- bioRxiv
- Date Published:
- Format(s):
- Medium: X
- Institution:
- bioRxiv
- Sponsoring Org:
- National Science Foundation
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