Long-term monitoring of egg-laying cycle using ultrasonography reveals the reproductive dynamics of circulating sex steroids in an oviparous catshark, Scyliorhinus torazame

Inoue, Tatuya; Shimoyama, Koya; Saito, Momoko; Wong, Marty Kwok‐Shing; Ikeba, Kiriko; Nozu, Ryo; Matsumoto, Rei; Murakumo, Kiyomi; Sato, Keiichi; Tokunaga, Kotaro; Kofuji, Kazuya; Takagi, Wataru; Hyodo, Susumu

doi:10.1016/j.ygcen.2022.114076

Cited by 8 publications

(19 citation statements)

References 63 publications

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“…Adult female catsharks were transported from the Ibaraki Prefectural Oarai Aquarium to the Atmosphere and Ocean Research Institute and kept in 1,000 and 3,000 L holding tanks with recirculating natural seawater at 16°C, maintaining a constant photoperiod (12 h light:12 h dark). The egg-laying cycle of catshark occurs approximately once every two or three weeks (Inoue et al, 2022). The fertilized eggs were manually collected from the cloaca of females, tagged to identify the date of oviposition, and subsequently placed in a separate tank away from adult individuals.…”

Section: Methodsmentioning

confidence: 99%

Low microbial abundance and community diversity within the egg capsule of the oviparous cloudy catshark (Scyliorhinus torazame) during oviposition

Takagi,

Masuda,

Shimoyama

et al. 2024

Preprint

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Vertebrate embryos are protected from bacterial infection by various maternally derived immune factors before the embryonic organs are fully developed. However, the defense mechanisms employed by elasmobranch embryos during development remain poorly understood. This study attempted to elucidate the embryonic defense mechanism of elasmobranchs by investigating the intracapsular environment of freshly laid eggs of the oviparous cloudy catshark (Scyliorhinus torazame). The egg capsule of oviparous elasmobranchs is tightly sealed until pre-hatching (early opening of the egg capsule), after which seawater flows into the capsule and the embryos are consequently exposed to the surrounding seawater. We first experimentally examined the resistance of embryos to potential bacterial infections and found that the early embryos were highly vulnerable to environmental pathogens, suggesting that the embryos are protected from the threat of infection before pre-hatching. Indeed, the intracapsular environment of freshly laid eggs exhibited a significantly low bacterial density that was maintained until pre-hatching. Furthermore, the microbiome inside eggs just after oviposition differed markedly from the microbiomes of rearing seawater and adult oviducal gland epithelia; these eggs were predominantly populated by an unidentified genus of Sphingomonadaceae. Overall, this study provides compelling evidence that early embryos of oviparous cloudy catshark are incubated in a clean intracapsular environment that potentially plays a significant role in embryonic development in oviparous elasmobranchs. Our results suggest that maintenance of this clean condition might be attributable to bactericidal or bacteriostatic activities associated with the egg jelly and/or oviducal gland.

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Section: Methodsmentioning

confidence: 99%

Low microbial abundance and community diversity within the egg capsule of the oviparous cloudy catshark (Scyliorhinus torazame) during oviposition

Takagi,

Masuda,

Shimoyama

et al. 2024

Preprint

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“…After acclimating in the holding tanks for at least 2 weeks, experimental fish (total length, 43.1 ± 1.8 cm; body weight, 364.4 ± 41.8 g; mean ± S.E.M.) were transferred to a 1000 L tank with a low water level for ultrasound investigation [ 4 ]. Individuals were identified by a tag tied to the dorsal fin.…”

Section: Methodsmentioning

confidence: 99%

“…The capsulated eggs are then retained in the lower oviducts for a certain period, such as 1–2 weeks, prior to oviposition. Following oviposition, the female catshark fertilizes the next ovulated eggs using the stored sperm again without mating [ 4 ]. These features complicate the research methods for determining the timing of fertilization and subsequent reproductive events, and thus limit progress in the understanding of reproductive physiology in cartilaginous fishes, despite its importance phylogenetically, ecologically, and physiologically.…”

Section: Introductionmentioning

confidence: 99%

“…We recently introduced a portable ultrasound device to monitor encapsulated eggs in oviducts and succeeded in assessing the egg-laying cycles of oviparous cloudy catshark Scyliorhinus torazame for 6 months [ 4 ]. Furthermore, concomitant measurement of plasma sex steroids revealed cyclic patterns of E2, testosterone (T), and P4 levels during the egg-laying cycle [ 4 ]. In particular, a surge in plasma P4 was consistently observed 2 days prior to the appearance of capsulated eggs in oviducts.…”

Section: Introductionmentioning

confidence: 99%

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Progesterone initiates tendril formation in the oviducal gland during egg encapsulation in cloudy catshark (Scyliorhinus torazame)

et al. 2023

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The diverse reproductive strategies of elasmobranchs (sharks, rays, and skates) have attracted research attention, but the endocrine control of reproduction is still incompletely known in elasmobranchs. By long-term monitoring of the egg-laying cycle in cloudy catsharks (Scyliorhinus torazame), we recently demonstrated a transient increase in plasma progesterone (P4) levels just prior to the appearance of the capsulated eggs in the oviducts. In the present study, we examined the in vivo effects of P4 administration in mature female cloudy catsharks. Although no capsulated eggs were observed following the implantation of P4-containing silicone tubing, we did find dark swollen oviducts in the abdominal cavity, in which clumps of long and coiled tendrils were observed. The tendril is an extension of the egg capsule, and the formation of the egg capsule begins with the tendril before main capsule formation. During the period of P4 implantation, the tendrils elongated, and their diameters were significantly increased on day 2 of treatment. Tendril formation was also confirmed on the day of endogenous P4 surge. Tendrils were not formed in catsharks implanted with estradiol-17β or testosterone. Histological analysis of the oviducal gland revealed that P4 implantation induced the secretion of tendril materials from the secretory tubules in the baffle zone, while the tendril materials were stored in the cytoplasm of the secretory cells under low P4 condition. Morphometrically, the area of secreted luminal materials in the secretory tubules was highly correlated to the diameter of tendrils. Our results suggest that the P4 surge during the egg-laying cycle serves as a trigger for egg capsule formation in the oviducal gland of cloudy catshark, but the hormonal signals were incomplete as the main capsule was not formed. Further studies are required to identify the hormones required for ovulation and formation of the main egg capsule.

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“…First, they are rather small and easy to maintain in a laboratory aquarium. Second, they are oviparous and spawn approximately once every 2–3 weeks in laboratory tanks (Inoue et al, 2022 ), so developing embryos are easily obtained. Furthermore, genomic data acquired through whole‐genome sequencing are available, which makes various molecular biological analyses easier (Hara et al, 2018 ; Kuraku, 2021 ).…”

Section: Introductionmentioning

confidence: 99%

In vitro and in vivo gene transfer in the cloudy catshark Scyliorhinus torazame

et al. 2022

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Cartilaginous fishes have various unique physiological features such as a cartilaginous skeleton and a urea-based osmoregulation strategy for adaptation to their marine environment. Also, because they are a sister group of bony vertebrates, understanding their unique features is important from an evolutionary perspective. However, genetic engineering based on gene functions as well as cellular behavior has not been effectively utilized in cartilaginous fishes. This is partly because their reproductive strategy involves internal fertilization, which results in difficulty in microinjection into fertilized eggs at the early developmental stage. Here, to identify efficient gene transfer methods in cartilaginous fishes, we examined the effects of various methods both in vitro and in vivo using the cloudy catshark, a candidate model cartilaginous fish species. In all methods, green fluorescent protein (GFP) expression was used to evaluate exogenous gene transfer. First, we examined gene transfer into primary cultured cells from cloudy catshark embryos by lipofection, polyethylenimine (PEI) transfection, adenovirus infection, baculovirus infection, and electroporation. Among the methods tested, lipofection, electroporation, and baculovirus infection enabled the successful transfer of exogenous genes into primary cultured cells. We then attempted in vivo transfection into cloudy catshark embryos by electroporation and baculovirus infection. Although baculovirus-injected groups did not show GFP fluorescence, electroporation successfully introduced GFP into muscle cells. Furthermore, we succeeded in GFP transfer into adult tissues by electroporation. The in vitro and in vivo gene transfer methods that worked in this study may open ways for genetic manipulation including knockout experiments and cellular lineage analysis in cartilaginous fishes.

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Long-term monitoring of egg-laying cycle using ultrasonography reveals the reproductive dynamics of circulating sex steroids in an oviparous catshark, Scyliorhinus torazame

Cited by 8 publications

References 63 publications

Low microbial abundance and community diversity within the egg capsule of the oviparous cloudy catshark (Scyliorhinus torazame) during oviposition

Low microbial abundance and community diversity within the egg capsule of the oviparous cloudy catshark (Scyliorhinus torazame) during oviposition

Progesterone initiates tendril formation in the oviducal gland during egg encapsulation in cloudy catshark (Scyliorhinus torazame)

In vitro and in vivo gene transfer in the cloudy catshark Scyliorhinus torazame

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