Hiroki Higashiyama

The gallbladder is the hepatobiliary organ for storing and secreting bile fluid, and is a synapomorphy of extant vertebrates. However, this organ has been frequently lost in several lineages of birds and mammals, including rodents. Although it is known as the traditional problem, the differences in development between animals with and without gallbladders are not well understood. To address this research gap, we compared the anatomy and development of the hepatobiliary systems in mice (gallbladd

The anterior end of the mammalian face is characteristically composed of a semimotile nose, not the upper jaw as in other tetrapods. Thus, the therian nose is covered ventrolaterally by the "premaxilla," and the osteocranium possesses only a single nasal aperture because of the absence of medial bony elements. This stands in contrast to those in other tetrapods in whom the premaxilla covers the rostral terminus of the snout, providing a key to understanding the evolution of the mammalian face. H

The trigeminal, the fifth cranial nerve of vertebrates, represents the rostralmost component of the nerves assigned to pharyngeal arches. It consists of the ophthalmic and maxillomandibular nerves, and in jawed vertebrates, the latter is further divided into two major branches dorsoventrally. Of these, the dorsal one is called the maxillary nerve because it predominantly innervates the upper jaw, as seen in the human anatomy. However, developmentally, the upper jaw is derived not only from the d

The gallbladder excretes cytotoxic bile acids into the duodenum through the cystic duct and common bile duct system. <i>Sox17</i> haploinsufficiency causes biliary atresia-like phenotypes and hepatitis in late organogenesis mouse embryos, but the molecular and cellular mechanisms underlying this remain unclear. In this study, transcriptomic analyses revealed the early onset of cholecystitis in <i>Sox17</i>^+/- embryos, together with the appearance of ectopic cystic duct-like epithelia

The vagus nerve, or the tenth cranial nerve, innervates the heart in addition to other visceral organs, including the posterior visceral arches. In amniotes, the anterior and posterior cardiac branches arise from the branchial and intestinal portions of the vagus nerve to innervate the arterial and venous poles of the heart, respectively. The evolution of this innervation pattern has yet to be elucidated, due mainly to the lack of morphological data on the vagus in basal vertebrates. To investig

The biliary tract is a well-branched ductal structure that exhibits great variation in morphology among vertebrates. Its function is maintained by complex constructions of blood vessels, nerves, and smooth muscles, the so-called hepatobiliary system. Although the mouse (Mus musculus) has been used as a model organism for humans, the morphology of its hepatobiliary system has not been well documented at the topographical level, mostly because of its small size and complexity. To reconcile this, w

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 exte

Although the gallbladder is one of the characteristic component of the vertebrate body, it has been independently lost in several lineages of mammals and birds. Gallbladder loss is a widely reported phenomenon; however, there have been few descriptive comparisons of entire hepatobiliary structures between birds with and without a gallbladder. Here, we discuss the evolution of avian hepatobiliary morphology by describing the gross anatomy of the hepatobiliary system in the quail and pigeon. Quail

Biliary atresia (BA) is a rare neonatal disease characterized by inflammation and obstruction of the extrahepatic bile ducts (EHBDs). The Sox17-haploinsufficient (Sox17^+/- ) mouse is an animal model of BA that encompasses bile duct injury and subsequent BA-like inflammation by the neonatal stage. Most Sox17^+/- neonates die soon after birth, but some Sox17^+/- pups reach adulthood and have a normal life span, unlike human BA. However, the phenotype and BA-derived s

The maxillofacial region is one of the most complex areas in the vertebrate body plan. The homology of the upper jaw bones remain controversial, both between mammals and nonmammalian amniotes and among humans and other mammals, leading to various hypotheses on how this region evolved from ancestral amniotes to humans. As a key mammalian model, the mouse (Mus musculus) is vital for unraveling the evolution and development of the maxillofacial region experimentally. However, limited detailed morph

Abstract The anatomical framework of the jawbones is highly conserved among most of the Osteichthyes, including the tetrapods. However, our recent study suggested that the premaxilla, the rostralmost upper jaw bone, was rearranged during the evolution of therian mammals, being replaced by the septomaxilla at least in the lateral part. In the present study, to understand more about the process of evolution from the ancestral upper jaw to the therian face, we re‐examined the development of the the

Abstract Coronary arteries are part of the vascular system that nourishes the heart; they are generally considered a synapomorphy of jawed vertebrates. However, the so-called coronary arteries originated from different body parts in amniotes and other groups, and the evolution of these arteries remains unclear. Here we propose that the amniote coronary arteries were newly obtained, overriding the ancestral arterial systems. In mouse ( Mus musculus ) and quail ( Coturnix japonica ) embryos, the a

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 two lineages, Myxininae and Eptatretinae. Usually, textbook illustrations of hagfish anatomy reflect the morphology of the former lineage, especially Myxine glutinosa , with its single pair of external branc