Zebrafish larval nitrogen excretion is flexible and resilient to loss of rhesus glycoproteins
- 1Radboud University
Abstract
Nitrogenous waste excretion is essential for all developmental stages of fish. Embryonic fish excrete urea, transitioning to cutaneous and later branchial ammonia excretion. In zebrafish, ammonia excretion involves rhesus glycoproteins Rhbg and Rhcgb in keratinocytes and ionocytes, but the developmental moment they appear in the gill remains unclear. Potential redundancy between Rhbg and Rhcgb in ammonia excretion is also not fully investigated, nor is the difference in response to low pH. We hypothesized that rhesus glycoproteins are partially redundant, and that they differ in their response to low pH as ammonia excretion enables ionocytes to exchange Na+ and H+ (Rh-NHE-metabolon). We predicted that a loss of rhbg or rhcgb induces compensatory responses. We characterized the transition from urea to branchial ammonia excretion from 0 to 8 days-post fertilization (dpf) and the response to pH 5.0 on the expression and localization of rhesus glycoproteins in control zebrafish and rhbg or rhcgb-crispants. Effects of high external ammonia (HEA, 500 M NH4Cl) and 10 mM HEPES-buffering were further characterized in rhcgb-crispants. Rhag and Rhbg appeared in the gill at 5 dpf, while Rhcgb appeared at 6 dpf. A loss of rhbg or rhcgb did not impact baseline N-excretion, illustrating that zebrafish can maintain ammonia excretion without the full complement of rhesus glycoproteins. We observed no compensatory increase in rhesus glycoproteins, but expression of the transporter hippocampus-abundant transcript 1b increased. HEA-exposed rhcgb-crispants switched to urea as primary nitrogen waste. Together, these findings underline the plasticity of the larval in dealing with nitrogenous waste.
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BibTeX
@misc{mes2026zebrafish,
title = {{Zebrafish larval nitrogen excretion is flexible and resilient to loss of rhesus glycoproteins}},
author = {W. Mes and R. Haanen and A. Arshad and P. H. M. Klaren and M. J. M. Schaaf and E. Faught and T. Nakada and M. A. H. J. van Kessel and M. Gorissen},
howpublished = {bioRxiv},
year = {2026},
month = aug,
doi = {10.64898/2026.08.28.747819},
url = {https://www.biorxiv.org/content/10.64898/2026.08.28.747819v1},
note = {CC BY-NC-ND},
}
RIS
TY - UNPB
TI - Zebrafish larval nitrogen excretion is flexible and resilient to loss of rhesus glycoproteins
AU - W. Mes
AU - R. Haanen
AU - A. Arshad
AU - P. H. M. Klaren
AU - M. J. M. Schaaf
AU - E. Faught
AU - T. Nakada
AU - M. A. H. J. van Kessel
AU - M. Gorissen
PY - 2026
DA - 2026/08/28
PB - bioRxiv
DO - 10.64898/2026.08.28.747819
UR - https://www.biorxiv.org/content/10.64898/2026.08.28.747819v1
AB - Nitrogenous waste excretion is essential for all developmental stages of fish. Embryonic fish excrete urea, transitioning to cutaneous and later branchial ammonia excretion. In zebrafish, ammonia excretion involves rhesus glycoproteins Rhbg and Rhcgb in keratinocytes and ionocytes, but the developmental moment they appear in the gill remains unclear. Potential redundancy between Rhbg and Rhcgb in ammonia excretion is also not fully investigated, nor is the difference in response to low pH. We hypothesized that rhesus glycoproteins are partially redundant, and that they differ in their response to low pH as ammonia excretion enables ionocytes to exchange Na+ and H+ (Rh-NHE-metabolon). We predicted that a loss of rhbg or rhcgb induces compensatory responses. We characterized the transition from urea to branchial ammonia excretion from 0 to 8 days-post fertilization (dpf) and the response to pH 5.0 on the expression and localization of rhesus glycoproteins in control zebrafish and rhbg or rhcgb-crispants. Effects of high external ammonia (HEA, 500 M NH4Cl) and 10 mM HEPES-buffering were further characterized in rhcgb-crispants. Rhag and Rhbg appeared in the gill at 5 dpf, while Rhcgb appeared at 6 dpf. A loss of rhbg or rhcgb did not impact baseline N-excretion, illustrating that zebrafish can maintain ammonia excretion without the full complement of rhesus glycoproteins. We observed no compensatory increase in rhesus glycoproteins, but expression of the transporter hippocampus-abundant transcript 1b increased. HEA-exposed rhcgb-crispants switched to urea as primary nitrogen waste. Together, these findings underline the plasticity of the larval in dealing with nitrogenous waste.
ER -