Develop. Growth Differ. (2005) 47, 357–366

Review

Establishment of a chick embryo model for analyzing liver development and a search for candidate genes

Yuji Yokouchi*

Division of Pattern Formation, Department of Organogenesis, Institute of Molecular Embryology and Genetics, Kumamoto University, 4-24-1, Kuhonji, Kumamoto 862-0976, Japan

The liver plays a crucial role in metabolism. There is considerable interest in how the liver develops, as suchknowledge could prove of importance in regenerative medicine. However, our understanding of liverdevelopment remains somewhat limited. We have developed a model system using the chick embryo that iscost effective and is easy to manipulate experimentally. We performed four fundamental studies: (i)construction of an atlas of the developing chick liver; (ii) identi cation of differentiation marker genes in thedeveloping chick embryo; (iii) development of germ-layer speci c electroporation; and (iv) establishment oforgan culture from the developing chick liver. Using this system, we have been able to demonstrate thefunctions of candidate genes within a shorter period and in a more cost-effective manner. In parallel with theestablishment of this system, we examined the expression patterns of genes known to be required for organdevelopment in the developing chick embryo in order to identify genes also involved in liver development. Todate, we have found sixteen genes that are expressed in the developing chick liver (GELD, genes expressedin liver development). This knowledge will be fundamental to the establishment of the basic technology forengineering liver tissue in the future.

Key words: chick, embryonic liver, epithelio–mesenchymal interaction, marker gene, organogenesis.

Introduction

A functioning liver is crucial for normal metabolism.The liver has a highly organized microstructure thatenables it to perform its function. This microstructureis composed mainly of three distinct cell types:parenchymal cells, epithelial cells of the bile duct,and endothelial cells of the sinusoids. These tissuesare enveloped by mesenchymal cells of the septumtransversum.

The microstructure of the liver develops fromepithelio–mesenchymal interactions between threeembryonic tissues: liver bud from foregut endoderm,septum transversum mesenchyme, and endothelialcells of primary sinusoids. Despite their differentembryonic origins, they selectively migrate throughthe septum transversum region and give rise to ahighly organized intermingled structure between theprimary hepatic cords and the primary sinusoids.

*Author to whom all correspondence should be addressed.Email: yokouchi@kaiju.medic.kumamoto-u.ac.jpReceived 17 May 2005; accepted 16 June 2005.

To date, despite considerable interest, our under-standing of the hepatic developmental program atthe molecular level is somewhat limited. This insuf -ciency is now a barrier to in vitro reconstruction ofliver tissue from embryonic or somatic stem cells.We have developed a model system using the chickembryo to enable rapid investigation of the molecularmechanisms of liver development. The chick embryohas several advantages over the mouse embryoas a model to study organogenesis. Among theseadvantages are that it is more cost-effective, can beeasily manipulated, and can be used for transgenesiswith either virus vectors or electroporation. Indeed,the molecular mechanisms of limb development,somitogenesis, patterning of the neural tube, and dif-ferentiation of the gastric gland have been revealedusing the chick embryo.

Although the chick embryo was widely used toanalyze hepatogenesis until the late 1970s (LeDouarin 1975), over the last three decades it hasbeen seldom exploited. As a result, despite itsadvantages as a model for embryology, study of liverdevelopment in the chick have not progressed well,