Meeting Abstract

65.2  Wednesday, Jan. 6  The development and evolution of axial skeleton of the hagfish OTA, K*; FUJIMOTO, S; OISI, Y; KURATANI, S; RIKEN CDB, Kobe; RIKEN CDB, Kobe; RIKEN CDB, Kobe; RIKEN CDB, Kobe ota_kinya@cdb.riken.jp

Extant jawless vertebrates consist of lampreys and hagfishes. According to recent molecular phylogenetic analysis, these two groups are clustered together into the same clade, so called “cyclostomes” and this clade is placed as sister to jawed vertebrates. Although the monophyletic relationship of extant jawless vertebrates is supported by a large amount of molecular sequence data, the apparently primitive morphology of hagfishes is a matter of debate. For example, the absence of vertebrae is still considered as strong evidence that hagfishes are placed at the basal position of the phylogenetic tree of vertebrates, in the field of paleontology. To address whether this morphology of hagfishes is the derived or ancestral condition, we conducted the developmental study in the Japanese inshore hagfish (Eptatretus burgeri), especially focusing on the somite derivatives. We performed a detailed histological observation and analyzed the expression patterns of Pax1/9 and Twist genes in the different stages of embryos. Our results show that the ventral somite cells de-epithelized and expressed these two genes, suggesting that the animal has sclerotome which is known to differentiate into vertebrae in gnathostomes. Based on these evidences, we inferred the evolutionary history of the axial skeleton of the early vertebrates.