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Muramatsu B, Suzuki DG, Suzuki M, Higashiyama H. Gross anatomy of the Pacific hagfish, Eptatretus burgeri, with special reference to the coelomic viscera. Anat Rec (Hoboken) 2024; 307:155-171. [PMID: 36958942 DOI: 10.1002/ar.25208] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 12/15/2022] [Revised: 02/06/2023] [Accepted: 03/08/2023] [Indexed: 03/25/2023]
Abstract
Hagfish (Myxinoidea) are a deep-sea taxon of cyclostomes, the extant jawless vertebrates. Many researchers have examined the anatomy and embryology of hagfish to shed light on the early evolution of vertebrates; however, the diversity within hagfish is often overlooked. Hagfish have three lineages, Myxininae, Eptatretinae, and Rubicundinae. Usually, textbook illustrations of hagfish anatomy reflect the morphology of the Myxininae lineage, especially Myxine glutinosa, with its single pair of external branchial pores. Here, we instead report the gross anatomy of an Eptatretinae, Eptatretus burgeri, which has six pairs of branchial pores, especially focusing on the coelomic organs. Dissections were performed on fixed and unfixed specimens to provide a guide for those doing organ- or tissue-specific molecular experiments. Our dissections revealed that the ventral aorta is Y-branched in E. burgeri, which differs from the unbranched morphology of Myxine. Otherwise, there were no differences in the morphology of the lingual apparatus or heart in the pharyngeal domain. The thyroid follicles were scattered around the ventral aorta, as has been reported for adult lampreys. The hepatobiliary system more closely resembled those of jawed vertebrates than those of adult lampreys, with the liver having two lobes and a bile duct connecting the gallbladder to each lobe. Overall, the visceral morphology of E. burgeri does not differ significantly from that of the known Myxine at the level of gross anatomy, although the branchial morphology is phylogenetically ancestral compared to Myxine.
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Affiliation(s)
- Banri Muramatsu
- Department of Biological Science, Graduate School of Science, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Daichi G Suzuki
- Faculty of Life and Environmental Sciences, University of Tsukuba, Tennodai, Tsukuba, 305-8572, Japan
| | - Masakazu Suzuki
- Department of Biological Science, Graduate School of Science, Shizuoka University, Shizuoka, 422-8529, Japan
| | - Hiroki Higashiyama
- Department of Physiological Chemistry and Metabolism, Graduate School of Medicine, The University of Tokyo, 7-3-1, Hongo, Bunkyo-ku, Tokyo, 113-0033, Japan
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Shiojiri N, Hirose H, Ota N, Sekiguchi J, Matsubara S, Kawakami H. Changes of biliary cilia, smooth muscle tissue distribution, innervation and extracellular matrices during morphological evolution of hepatic architectures in vertebrates. Ann Anat 2023; 250:152148. [PMID: 37591347 DOI: 10.1016/j.aanat.2023.152148] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [MESH Headings] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/08/2023] [Revised: 07/10/2023] [Accepted: 07/31/2023] [Indexed: 08/19/2023]
Abstract
BACKGROUND The liver architecture of vertebrates can be classified into two types, the portal triad type (having periportal bile ducts) and the non-portal triad type (having bile ducts independent of the course of portal veins). The former is typically detectable in livers of tetrapods and cartilaginous fish, and its ancestral state is found in the hagfish, an earliest diverged lineage among vertebrates. Teleosts other than osteoglossomorphs have the latter. The aim of the present study is to reveal the changes of the hepatic innervation, biliary cilia and smooth muscle distribution, and extracellular matrices along vertebrate evolution with attention to the two types of liver architectures. METHODS The hepatic innervation, biliary cilia and smooth muscle distribution, and collagen deposition were immunohistochemically and histochemically compared among livers of various vertebrates, using anti-acetylated tubulin and anti-α-smooth muscle actin antibodies, and Sirius red staining. These were also ultrastructurally examined. RESULTS Although the hagfish liver had periportal intrahepatic bile ducts and ductules as detected in mammalian livers, it lacked smooth muscles around bile ducts and portal veins. Extracellular matrices in their connective tissues had thick collagen fibers. Its innervation was restricted to intrahepatic bile ducts and portal veins in the hilum. In livers of other vertebrates, including teleosts, the innervation was broadly detectable, especially around bile ducts, hepatic arteries and portal veins (afferent vessels), but not around central veins (efferent vessels). The chondrichthyans ultrastructurally had smooth muscle tissue around bile ducts. Cilia distribution was confirmed in intrahepatic bile ducts of tetrapods and basal actinopterygians. Teleosts other than osteoglossomorphs lacked cilia in their intrahepatic bile ducts. CONCLUSIONS The liver architecture of the hagfish may be unique for innervation and extracellular matrices. Hepatic innervation may not have occurred in vertebrate ancestors. Hepatic innervation in bile ducts, hepatic arteries and portal veins may have been conserved among the extant jawed vertebrates. Cilia distribution in bile ducts may have changed during evolution of actinopterygians.
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Affiliation(s)
- Nobuyoshi Shiojiri
- Department of Biology, Faculty of Science, Shizuoka University, 836 Oya, Suruga-ku, Shizuoka 422-8529, Japan; Graduate School of Science and Technology, Shizuoka University, 836 Oya, Suruga-ku, Shizuoka 422-8529, Japan.
| | - Haruka Hirose
- Department of Biology, Faculty of Science, Shizuoka University, 836 Oya, Suruga-ku, Shizuoka 422-8529, Japan
| | - Noriaki Ota
- Graduate School of Science and Technology, Shizuoka University, 836 Oya, Suruga-ku, Shizuoka 422-8529, Japan
| | - Junri Sekiguchi
- Laboratory for Electron Microscopy, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka-shi, Tokyo 181-8611, Japan; Department of Anatomy, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka-shi, Tokyo 181-8611, Japan
| | - Sachie Matsubara
- Laboratory for Electron Microscopy, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka-shi, Tokyo 181-8611, Japan; Department of Anatomy, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka-shi, Tokyo 181-8611, Japan
| | - Hayato Kawakami
- Laboratory for Electron Microscopy, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka-shi, Tokyo 181-8611, Japan; Department of Anatomy, Kyorin University School of Medicine, 6-20-2 Shinkawa, Mitaka-shi, Tokyo 181-8611, Japan
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Immunohistological analysis on distribution of smooth muscle tissues in livers of various vertebrates with attention to different liver architectures. Ann Anat 2020; 233:151594. [PMID: 32911068 DOI: 10.1016/j.aanat.2020.151594] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 04/09/2020] [Revised: 08/13/2020] [Accepted: 08/19/2020] [Indexed: 12/21/2022]
Abstract
BACKGROUND The liver architecture of vertebrates can be classified into two types, the portal triad type (having periportal bile ducts) and the non-portal triad type (having non-periportal bile ducts). The former is detectable from the hagfish, which is the most ancestral vertebrate, to tetrapod livers whereas many actinopterygian livers have the latter. The aim of the present study is to reveal the distribution of smooth muscle tissue in livers of various vertebrates with attention to their architectures. METHODS Smooth muscle was immunohistochemically compared in hepatic blood vessels and bile ducts of various vertebrates, using an anti-alpha-smooth muscle actin (ASMA) antibody. RESULTS Smooth muscle was noted in the gallbladder and hepatic artery in all vertebrates, including the hagfish. Bile ducts having ASMA-positive smooth muscles were absent in the hagfish, but detected in the Chondrichthyes and conserved in actinopterygians with or without portal triads during the evolution of vertebrates. In tetrapods having portal triads, reptiles had a tendency to have strongly ASMA-positive biliary smooth muscle tissues whereas other tetrapods had bile ducts with poor smooth muscle tissues. Although the hagfish livers never had ASMA-positive smooth muscle tissue in the walls of portal and central veins, it was observed in discontinuous distributions or not observed in portal veins and central veins of chondrichthyans and actinopterygians. By contrast, in most tetrapods, ASMA-positive smooth muscle tissue was detectable in portal veins, which supported the adjacent endothelial cells as a circular layer. Central veins did not consistently have smooth muscle tissue in these groups. DISCUSSION AND CONCLUSION The hagfish liver may retain more ancestral characteristics than other vertebrates in terms of smooth muscle distribution in the vascular and biliary systems. Actinopterygians might have a different mechanism of bile transport from tetrapods from their smooth muscle distribution in intrahepatic bile ducts. The circular smooth muscle distribution in portal veins might be a characteristic acquired by tetrapods.
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