Characterization of the Column and Autocellular Junctions That Define the Vasculature of Gill Lamellae

Akira Kato ¹, Korefumi Nakamura ¹, Hisayuki Kudo ¹, Yen Ha Tran ¹, Yoko Yamamoto ¹, Hiroyuki Doi ¹ and Shigehisa Hirose ^1*

¹ Department of Biological Sciences, Tokyo Institute of Technology, Yokohama, Japan (AK,KN,HK,YHT,YY,SH); Shimonoseki Marine Science Museum "Kaikyokan", Shimonoseki Academy of Marine Science, Shimonoseki, Japan (HD)

^* To whom correspondence should be addressed. E-mail: shirose{at}bio.titech.ac.jp.

Submitted on November 22, 2006
Accepted on 1 May 2007

	Abstract

Novel adhesion junctions have been characterized that are formed at the interface between pillar cells and collagen columns, both of which are essential constituents of the gill lamellae in fish. We termed these junctions the "column junction" and "autocellular junction" and determined their molecular compositions by immunofluorescence microscopy using pufferfish. We visualized collagen columns by concanavalin A staining and found that the components of integrin-mediated cell-matrix adhesion, such as talin, vinculin, paxillin, and fibronectin, were concentrated on plasma membrane surrounding collagen columns (column membranes). This connection is analogous to the focal adhesion of cultured mammalian cells, dense plaque of smooth muscle cells, and myotendinous junction of skeletal muscle cells. We named this connection the "column junction". In the cytoplasm near the column, actin fibers, actinin, and phosphorylated myosin light chain of 20 kDa are densely located, suggesting the contractile nature of pillar cells. The membrane infoldings surrounding the collagen columns were found to be connected by the autocellular junction whose components are highly tyrosine-phosphorylated and contain the tight junction protein ZO-1. This study represents the first molecular characterization and fluorescence visualization of column and autocellular junctions involved in both maintaining structural integrity and the hemodynamics of the branchial lamellae.

Key Words: collagen column, column membrane, column junction, autocellular junction, contractile apparatus, focal adhesion analog, gill structure, pillar cell

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