Targeted gene expression in the chicken eye by in ovo electroporation.

The embryonic lens is an attractive model system to study the molecular mechanisms that regulate cell proliferation and differentiation [1-4]. The chicken lens has a long history serving as an in vivo model for such studies because of its easy accessibility for surgical manipulation [5-8]. For example, in the classical lens inversion experiment of Coulombre and Coulombre [9], the chicken embryo lens was surgically rotated 180° so that the epithelial cells faced the vitreous body and neural retina. As a result, the former lens epithelial cells elongated and differentiated into fiber cells in a few days. This experiment provided evidence that the inductive signals for lens fiber cell differentiation were present in the vitreous and likely originated from the retina. In the past a few decades, although much effort has been focused on identifying the inducers for lens epithelial to fiber cell differentiation [8,1012], the endogenous factors for lens fiber cell differentiation have not identified in either chicken or mammalian eyes. A powerful approach to reveal the molecular mechanisms of development is to manipulate gene expression and examine the consequences in vivo. With a lens specific promoter to drive transgene expression, the mouse lens has been widely used for gene function analysis [13-16]. For example, different members of the FGF family have been shown to induce premature differentiation of the anterior lens epithelial cells in transgenic mice [17,18]. Blocking FGF receptor (FGFR) activity in the mouse lens is carried out by expressing either a dominant negative form of FGFR1 [19-21] or a secreted form of FGFR3 [22]. This blocking inhibited normal lens fiber cell differentiation and resulted in smaller lenses in transgenic mice. These experiments suggest that, at least in the mouse, one or more members of the FGF family may play a critical role in fiber cell differentiation. Such experiments would be difficult to perform in the chicken embryo lens because of its limited accessibility to genetic manipulation. Therefore, despite the fact that much of our knowledge on lens development is based on the studies using the chicken embryo lens, it still remains unclear whether the signaling mechanism for fiber cell differentiation is evolutionally conserved between mammals and birds. In recent years, in ovo electroporation has become a powerful tool to examine gene function during chicken embryonic development [23,24]. The basic steps of this technique ©2004 Molecular Vision