Description of Embryonic Development of Spotted Green Pufferfish (Tetraodon nigroviridis)

Abstract

Pufferfish species of the Tetraodontidae family carry the smallest genomes among vertebrates. Their compressed genomes are thought to be enriched for functional DNA compared to larger vertebrate genomes, and they are important models for comparative genomics. The significance of pufferfish as model organisms in comparative genomics is due to the availability of two sequenced genomes, that of spotted green pufferfish (Tetraodon nigroviridis) and fugu (Takifugu rubripes). However, there is only a very limited utilization of pufferfish as an experimental model organism, due to the lack of established husbandry and developmental genetics protocols. In this study, we provide the first description of the normal embryonic development of Tetraodon nigroviridis. Embryos were obtained by in vitro fertilization of eggs, and subsequent development was monitored by brightfield microscopy at constant temperature. Tetraodon development was divided into distinct stages based on diagnostic morphological features, which were adopted from published literature on normal development of other fish species like medaka (Oryzias latipes), zebrafish (Danio rerio), and fugu. Tetraodon embryos show more similar morphologies to medaka than to zebrafish, reflecting its phylogenetic position. The early developmental stage series described in this study forms the foundation for the utilization of tetraodon as an experimental model organism for comparative developmental studies.

Embryonic development of the bullseye puffer Sphoeroides annulatus (Tetraodontidae): A morphofunctional approach to ontogenetic steps

“…At 40% epiboly, the cellular involution as a second morphogenetic movement forms the hypoblast, indicated by the germinal ring formation. This process is similar to that reported for T. ocellatus , T. rubripes , D. nigroviridis , and O. latipes (Chen, ; Iwamatsu, ;Uji et al, ; Zaucker et al, ). In contrast, in T. niphobles and D. rerio , the germinal ring appears after 50% epiboly (Gallego et al, ; Kimmel et al, ).…”

“…As in other teleosts, the processes that occur during this step (e.g., cortical reaction, karyogamy, bipolar differentiation, polyadenylation of transcripts from maternal origin) establish the structural condition from which the development begins. This step is equivalent to the zygote period ( sensu Kimmel, Ballard, Kimmel, Ullmann, & Schilling, ) described for other tetraodontids (Gallego, Yoshida, Kurokawa, Asturiano, & Fraser, ; Jang, Kang, & Han, ; Uji, Kurokawa, Hashimoto, Kasuya, & Suzuki, ; Zaucker et al, ), and its cell dynamics are similar to those described for other teleosts (Lange et al, 1974, as cited in Peňáz, ). However, because the fast‐structural dynamics between the activation onset and the blastodisc formation, it could be argued that this ontogenetic interval is a threshold and not a step as has been described typically in other teleosts (e.g., Balon, ; Cunningham & Balon, ; Kováč, ; Peňáz, ; Pinder & Gozlan, ).…”

“…Nevertheless, there are remarkable differences in the structural development between tetraodontids at the same n‐somite stages. For example, the optic primordium appears before the somite formation in S. annulatus and D. nigroviridis , while in T. rubripes and T. niphobles , it appears at 3‐somite stage (Gallego et al, ; Uji et al, ; Zaucker et al, ). In S. annulatus , the Kupffer's vesicle appears at 2‐somite stage, whereas in D. nigroviridis and T. rubripes it appears at 1‐somite and 6‐somite stages, respectively (Uji et al, ; Zaucker et al, ).…”

“…For example, the optic primordium appears before the somite formation in S. annulatus and D. nigroviridis , while in T. rubripes and T. niphobles , it appears at 3‐somite stage (Gallego et al, ; Uji et al, ; Zaucker et al, ). In S. annulatus , the Kupffer's vesicle appears at 2‐somite stage, whereas in D. nigroviridis and T. rubripes it appears at 1‐somite and 6‐somite stages, respectively (Uji et al, ; Zaucker et al, ). This interspecific heterochrony may originate in the differential gene expression related to Kupffer's vesicle morphogenesis (e.g., cas , ntl , oep , and irdr1 ; Essner, Amack, Nyholm, Harris, & Yost, ).…”

“…This structure has been reported for different taxa from order Tetraodontiformes (Leis, ). However, the amplitude of this structure is less evident in other tetraodontids, such as D. nigroviridis (Zaucker et al, ). The vesicular dermal sac is homologous to the fluid‐filled subdermal space (i.e., dorsal sinus, perivitelline sinus, and finfold) that presents free embryos of marine teleosts with pelagic spawning (e.g., G. morhua ).…”