Early development and neurogenesis of Temnopleurus reevesii

Abstract

Sea urchins are model non-chordate deuterostomes, and studying the nervous system of their embryos can aid in the understanding of the universal mechanisms of neurogenesis. However, despite the long history of sea urchin embryology research, the molecular mechanisms of their neurogenesis have not been well investigated, in part because neurons appear relatively late during embryogenesis. In this study, we used the species Temnopleurus reevesii as a new sea urchin model and investigated the detail of its development and neurogenesis during early embryogenesis. We found that the embryos of T. reevesii were tolerant of high temperatures and could be cultured successfully at 15-30°C during early embryogenesis. At 30°C, the embryos developed rapidly enough that the neurons appeared at just after 24 h. This is faster than the development of other model urchins, such as Hemicentrotus pulcherrimus or Strongylocentrotus purpuratus. In addition, the body of the embryo was highly transparent, allowing the details of the neural network to be easily captured by ordinary epifluorescent and confocal microscopy without any additional treatments. Because of its rapid development and high transparency during embryogenesis, T. reevesii may be a suitable sea urchin model for studying neurogenesis. Moreover, the males and females are easily distinguishable, and the style of early cleavages is intriguingly unusual, suggesting that this sea urchin might be a good candidate for addressing not only neurology but also cell and developmental biology.

Transforming growth factor‐β signal regulates gut bending in the sea urchin embryo

“…The expression and the functional data for TGF‐β family members in the early developmental stages of T. reevesii indicated that the gene regulatory network driving the dorsal–ventral axis formation was similar to that in other indirect developer sea urchin species. Combined with a previous report (Yaguchi et al., ), this result indicated that this species could be one of the model sea urchins in the study of developmental biology, particularly in analyzing axis formation during early embryogenesis. Currently, the identification of common features or biological phenomena and analyzing the detailed molecular mechanisms to show reproducible results is an important process.…”

“…In Japanese sea urchin developmental biology, to date, H. pulcherrimus has been the most frequently used model organism. However, based on a previous study (Yaguchi et al., ) and this paper, we show that T. reevesii can be used as a routinely available model sea urchin in Japanese labs. Therefore, the similar behavior of gut bending was the focus in this additional species, and the Alk4/5/7‐Smad2/3 pathway was involved in the gut‐bending step, which adds new information regarding morphogenesis of the sea urchin embryo.…”

“…In Japanese developmental biology using sea urchins, H. pulcherrimus has been the prominent model organism for decades. In 2015, however, our group reported that T. reevesii could be another model sea urchin that can be used in developmental biology because of its rapid development, tolerance of high temperature and high transparency (Yaguchi et al., ). In fact, T. reevesii is more beneficial for observing neurogenesis than H. pulcherrimus , which has a relatively longer developmental time to reach the neurogenic larval stages.…”

Troponin-I is present as an essential component of muscles in echinoderm larvae

“…To confirm whether the expression patterns of TnI are conserved among sea urchins, we investigated the protein expression patterns in another sea urchin, Temnopleurus reevesii 27. As observed in H. pulcherrimus , TnI was expressed in the esophagus, the esophageal muscle and the pyloric and anal sphincters, as well as in the ventral ectoderm (Fig.…”

Morphological diversity of blastula formation and gastrulation in temnopleurid sea urchins

“…The differences in the shape of the pseudopod-like structures among temnopleurids may be caused by different substances within the matrix. Recently, Yaguchi et al (2015) indicated that adhesion between blastomeres at the early cleavages was very loose, and that the blastomeres had many protrusions attached to the outer ECM and the hyaline layer at the cleavage furrow in T. reevesii . Also, it was difficult to divide each blastomere of the early cleavage-staged embryos of T. hardwickii and M. globulus because of the outer ECM and the hyaline layer (data not shown).…”