Opposing roles for Bmp signalling during the development of electrosensory lateral line organs

  1. Alexander S Campbell
  2. Martin Minařík
  3. Roman Franěk
  4. Michaela Vazačová
  5. Miloš Havelka
  6. David Gela
  7. Martin Pšenička
  8. Clare VH Baker

  • Curated by eLife

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    eLife assessment

    This study reports analysis of the formation of electrosensory ampullary organs in non-model organisms, the sterlet sturgeon. By using a combination of targeted gene knock-out and inhibition, the study provides overall convincing evidence for differential roles of BMP signaling in lateral-line development, with few aspects that could be improved. The study is particularly valuable for understanding the development of a still-mysterious sensory system, and for its evolutionary implications.

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Abstract

The lateral line system enables fishes and aquatic-stage amphibians to detect local water movement via mechanosensory hair cells in neuromasts, and many species to detect weak electric fields via electroreceptors (modified hair cells) in ampullary organs. Both neuromasts and ampullary organs develop from lateral line placodes, but the molecular mechanisms underpinning ampullary organ formation are understudied relative to neuromasts. This is because the ancestral lineages of zebrafish (teleosts) and Xenopus (frogs) independently lost electroreception. We identified Bmp5 as a promising candidate via differential RNA-seq in an electroreceptive ray-finned fish, the Mississippi paddlefish ( Polyodon spathula ; Modrell et al., 2017, eLife 6: e24197). In an experimentally tractable relative, the sterlet sturgeon ( Acipenser ruthenus ), we found that Bmp5 and four other Bmp pathway genes are expressed in the developing lateral line, and that Bmp signalling is active. Furthermore, CRISPR/Cas9-mediated mutagenesis targeting Bmp5 in G0-injected sterlet embryos resulted in fewer ampullary organs. Conversely, when Bmp signalling was inhibited by DMH1 treatment shortly before the formation of ampullary organ primordia, supernumerary ampullary organs developed. These data suggest that Bmp5 promotes ampullary organ development, whereas Bmp signalling via another ligand(s) prevents their overproduction. Taken together, this demonstrates opposing roles for Bmp signalling during ampullary organ formation.

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  1. Version published to 10.7554/elife.99798 on eLife
  2. eLife

    eLife assessment

    This study reports analysis of the formation of electrosensory ampullary organs in non-model organisms, the sterlet sturgeon. By using a combination of targeted gene knock-out and inhibition, the study provides overall convincing evidence for differential roles of BMP signaling in lateral-line development, with few aspects that could be improved. The study is particularly valuable for understanding the development of a still-mysterious sensory system, and for its evolutionary implications.

  3. eLife

    Reviewer #1 (Public Review):

    The authors were curious about the formation of the electrosensory lateral line, which is found in non-traditional model organisms. This issue has traditionally hampered studies because those organisms are not amenable to controlled experimental work.

    The authors skillfully use CRIPR-based technologies to overcome this limitation. Together with exceptionally good whole-mount in situ hybridisation, they produced a well-supported conclusion that Bmp signalling has different roles in the development of electrosensory ampullary organs.

    I would not entirely agree that Bmp signalling has "opposing" roles because the authors do not show evidence of opposition via gain-of-function experiments at different developmental times. Instead, they are simply different at different periods of organogenesis.

    The study is important for understanding the development of a still-mysterious sensory system, and for its implications in evolutionary biology more generally.

  4. eLife

    Reviewer #2 (Public Review):

    Campbell et al have described the dynamic pattern of two Bmps (Bmp5, Bmp4), one of their receptors (Acvr2a), putative joint inhibitors of the Bmp & Wnt pathways (sostdc1, apcdd1) and an effector of Bmp signaling phosph-Smad, in the experimentally tractable sterlet sturgeon to better understand the role of Bmp signaling in electroreceptor development. The role of Bmp signaling is poorly understood in the lateral line system. Furthermore, the development of electroreceptors in ampullary organs remains poorly understood as most recent analysis of lateral line development has focused on model organisms Xenopus and zebrafish, which the electroreceptors have been lost. They show that expression of these players is consistent with a role for Bmp signaling in electroreceptor development. Furthermore, they show that Bmp5 crispants have fewer ampullary organs. However, inhibition of Bmp signaling with the small molecule inhibitor DMH1 for 20 hours starting from stage 36 after hatching and before ampullary organ development results in supernumerary ampullary organ development. These strikingly different results lead the authors to conclude that Bmp signaling has opposing roles in ampullary organ development.

    These observations are interesting and the conclusions are supported by the data presented and the study makes important contributions to our understanding of the role of Bmp signaling in electroreceptor development in lateral line development. However, the study opens and leaves unresolved a number of questions. While a definitive answer to these questions may be outside the scope of this paper, some additional experiments may help strengthen the paper.

  5. Version published to 10.1101/2024.03.07.583945v2 on bioRxiv
  6. Version published to 10.1101/2024.03.07.583945v1 on bioRxiv