title: Expression of carbonic anhydrase IX in human fetal joints, ligaments and tendons: a potential marker of mechanical stress in fetal development?
abstract: Carbonic anhydrase type IX (CA9) is known to express in the fetal joint cartilage to maintain pH against hypoxia. Using paraffin-embedded histology of 10 human fetuses at 10-16 weeks of gestation with an aid of immunohistochemistry of the intermediate filaments, matrix components (collagen types I and II, aggrecan, versican, fibronectin, tenascin, and hyaluronan) and CA9, we observed all joints and most of the entheses in the body. At any stages examined, CA9-poisitive cells were seen in the intervertebral disk and all joint cartilages including those of the facet joint of the vertebral column, but the accumulation area was reduced in the larger specimens. Glial fibrillary acidic protein (GFAP), one of the intermediate filaments, expressed in a part of the CA9-positive cartilages. Developing elastic cartilages were positive both of CA9 and GFAP. Notably, parts of the tendon or ligament facing to the joint, such as the joint surface of the annular ligament of the radius, were also positive for CA9. A distribution of each matrix components examined was not same as CA9. The bone-tendon and bone-ligament interface expressed CA9, but the duration at a site was limited to 3-4 weeks because the positive site was changed between stages. Thus, in the fetal entheses, CA9 expression displayed highly stage-dependent and site-dependent manners. CA9 in the fetal entheses seemed to play an additional role, but it was most likely to be useful as an excellent marker of mechanical stress at the start of enthesis development.
authors.affiliation: Department of Anatomy, Chonbuk National University Medical School, Jeonju, Korea.
authors.forename: Ji Hyun
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Anatomy, Institute of Bioscience and Medical Technology, University of Tampere, Tampere, Finland.
authors.forename: Seppo
authors.initials: S
authors.lastname: Parkkila
authors.affiliation: Maxillofacial Anatomy, Department of Maxillofacial Biology, Tokyo Medical and Dental University Graduate School, Tokyo, Japan.
authors.forename: Shunichi
authors.initials: S
authors.lastname: Shibata
authors.affiliation: Department of Anatomy, Sapporo Medical University School of Medicine, Sapporo, Japan.
authors.forename: Mineko
authors.initials: M
authors.lastname: Fujimiya
authors.affiliation: Division of Internal Medicine, Iwamizawa Kojin-kai Hospital, Iwamizawa, Japan.
authors.forename: Gen
authors.initials: G
authors.lastname: Murakami
authors.affiliation: Department of Surgery and Research Institute of Clinical Medicine, Chonbuk National University Hospital, Chonbuk National University Medical School, Jeonju, Korea.
authors.forename: Baik Hwan
authors.initials: BH
authors.lastname: Cho
keywords: Carbonic anhydrase type IX; Enthesis; Human fetus; Intermediate filaments; Joints