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4 results on '"Naotaka Aburatani"'

1. Molecular and morphological investigations on the renal mechanisms enabling euryhalinity of red stingray Hemitrygon akajei

Author

Naotaka Aburatani, Wataru Takagi, Marty Kwok-Shing Wong, Shigehiro Kuraku, Chiharu Tanegashima, Mitsutaka Kadota, Kazuhiro Saito, Waichiro Godo, Tatsuya Sakamoto, and Susumu Hyodo

Subjects
cartilaginous fish, euryhalinity, osmoregulation, urine, nephron, membrane transporter, Physiology, QP1-981
Abstract

Most cartilaginous fishes live in seawater (SW), but a few exceptional elasmobranchs (sharks and rays) are euryhaline and can acclimate to freshwater (FW) environments. The plasma of elasmobranchs is high in NaCl and urea concentrations, which constrains osmotic water loss. However, these euryhaline elasmobranchs maintain high levels of plasma NaCl and urea even when acclimating to low salinity, resulting in a strong osmotic gradient from external environment to body fluid. The kidney consequently produces a large volume of dilute urine to cope with the water influx. In the present study, we investigated the molecular mechanisms of dilute urine production in the kidney of Japanese red stingray, Hemitrygon akajei, transferred from SW to low-salinity environments. We showed that red stingray maintained high plasma NaCl and urea levels by reabsorbing more osmolytes in the kidney when transferred to low salinity. RNA-seq and qPCR analyses were conducted to identify genes involved in NaCl and urea reabsorption under the low-salinity conditions, and the upregulated gene expressions of Na+-K+-Cl- cotransporter 2 (nkcc2) and Na+/K+-ATPase (nka) were found in the FW-acclimated individuals. These upregulations occurred in the early distal tubule (EDT) in the bundle zone of the kidney, which coils around the proximal and collecting tubules to form the highly convoluted structure of batoid nephron. Considering the previously proposed model for urea reabsorption, the upregulation of nkcc2 and nka not only causes the reabsorption of NaCl in the EDT, but potentially also supports enhanced urea reabsorption and eventually the production of dilute urine in FW-acclimated individuals. We propose advantageous characteristics of the batoid-type nephron that facilitate acclimation to a wide range of salinities, which might have allowed the batoids to expand their habitats.

Published
2022
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3. Facilitated NaCl Uptake in the Highly Developed Bundle of the Nephron in Japanese Red Stingray

Author

Naotaka, Aburatani, Wataru, Takagi, Marty Kwok-Sing, Wong, Mitsutaka, Kadota, Shigehiro, Kuraku, Kotaro, Tokunaga, Kazuya, Kofuji, Kazuhiro, Saito, Waichiro, Godo, Tatsuya, Sakamoto, and Susumu, Hyodo

Subjects
Animals, Nephrons, Skates, Fish, Sodium Chloride
Abstract

Batoidea (rays and skates) is a monophyletic subgroup of elasmobranchs that diverged from the common ancestor with Selachii (sharks) about 270 Mya. A larger number of batoids can adapt to low-salinity environments, in contrast to sharks, which are mostly stenohaline marine species. Among osmoregulatory organs of elasmobranchs, the kidney is known to be dedicated to urea retention in ureosmotic cartilaginous fishes. However, we know little regarding urea reabsorbing mechanisms in the kidney of batoids. Here, we performed physiological and histological investigations on the nephrons in the red stingray (

Published
2020

4. Facilitated NaCl Uptake in the Highly Developed Bundle of the Nephron in Japanese Red Stingray Hemitrygon akajei Revealed by Comparative Anatomy and Molecular Mapping

Author

Marty Kwok Sing Wong, Kotaro Tokunaga, Waichiro Godo, Susumu Hyodo, Kazuhiro Saito, Wataru Takagi, Shigehiro Kuraku, Tatsuya Sakamoto, Mitsutaka Kadota, Naotaka Aburatani, and Kazuya Kofuji

Subjects
0106 biological sciences, 0301 basic medicine, biology, urogenital system, Reabsorption, Zoology, Nephron, biology.organism_classification, 010603 evolutionary biology, 01 natural sciences, Catshark, Scyliorhinus torazame, 03 medical and health sciences, 030104 developmental biology, medicine.anatomical_structure, Houndshark, Stingray, medicine, Batoidea, Animal Science and Zoology, Stenohaline
Abstract

Batoidea (rays and skates) is a monophyletic subgroup of elasmobranchs that diverged from the common ancestor with Selachii (sharks) about 270 Mya. A larger number of batoids can adapt to low-salinity environments, in contrast to sharks, which are mostly stenohaline marine species. Among osmoregulatory organs of elasmobranchs, the kidney is known to be dedicated to urea retention in ureosmotic cartilaginous fishes. However, we know little regarding urea reabsorbing mechanisms in the kidney of batoids. Here, we performed physiological and histological investigations on the nephrons in the red stingray (Hemitrygon akajei) and two shark species. We found that the urine/plasma ratios of salt and urea concentrations in the stingray are significantly lower than those in cloudy catshark (Scyliorhinus torazame) under natural seawater, indicating that the kidney of stingray more strongly reabsorbs these osmolytes. By comparing the three-dimensional images of nephrons between stingray and banded houndshark (Triakis scyllium), we showed that the tubular bundle of stingray has a more compact configuration. In the compact tubular bundle of stingray kidney, the distal diluting tubule was highly developed and frequently coiled around the proximal and collecting tubules. Furthermore, co-expression of NKAα1 (Na+/K +-ATPase) and NKCC2 (Na+- K+-2Cl– cotransporter 2) mRNAs was prominent in the coiled diluting segment. These findings imply that NaCl reabsorption is greatly facilitated in the stingray kidney, resulting in a higher reabsorption rate of urea. Lowering the loss of osmolytes in the glomerular filtrate is likely favorable to the adaptability of batoids to a wide range of environmental salinity.

Published
2020

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