Gene manipulation of chick embryos in vitro, early chick culture, and long survival in transplanted eggs

Different gene transfer methods at the very early, early, late and whole embryonic stages in chicken

New technologies in gene transfer combined with experimental embryology make the chicken embryo an excellent model system for gene function studies. The techniques of in ovo electroporation, in vitro culture for ex ovo electroporation and retrovirus-mediated gene transfer have already been fully developed in chicken. Yet to our knowledge, there are no definite descriptions on the features and application scopes of these techniques. The survival rates of different in vitro culture methods were compared and the EGFP expression areas of different gene transfer techniques were explored. It was that the optimal timings of removing embryo for EC culture and Petri dish system was at E1.5 and E2.5, respectively; and optimal timing of injecting retrovirus is at E0. Results indicated that the EC culture, in ovo electroporation, the Petri dish system and retrovirus-mediated method are, respectively, suitable for the very early, early, late and whole embryonic stages in chicken. Comparison of different gene transfer methods and establishment of optimal timings are expected to provide a better choice of the efficient method for a particular experiment.

Electroporation: past, present and future

Gene transfer by electroporation has become an indispensable method for the study of developmental biology. The technique is applied not only in chick embryos but also in mice and other organisms. Here, a short history and perspectives of electroporation for gene transfer in vertebrates are described.

A simple technique for early in vivo electroporation of E1 chick embryos

BACKGROUND

The amenability of the chick embryo to a variety of manipulations has made it an ideal experimental model organism for over 100 years. The ability to manipulate gene function via in ovo electroporations has further revolutionized its value as an experimental model in the last 15 years. Although in ovo electroporations are simple to conduct in embryos ≥ E2, in ovo electroporations at early E1 stages have proven to be technically challenging due to the tissue damage and embryonic lethality such electroporations produce.

RESULTS AND CONCLUSIONS

Here we report our success with in vivo microelectroporations of E1 embryos as young as Hamburger-Hamilton Stage 4 (HH4). We provide evidence that such electroporations can be varied in size and can be spatially targeted. They cause minimal disruption of tissue-size, 3-dimensional morphology, cell survival, proliferation, and cell-fate specification. Our paradigm is easily adapted to a variety of experimental conditions since it does not depend upon the presence of a lumen to enclose the DNA solution during electroporation. It is thus compatible with the in vivo examination of E1 morphogenetic events (e.g., neural tube closure) where preservation of 3-dimensional morphology is critical.

Early arterial differentiation and patterning in the avian embryo model

Of the many models to study vascular biology the avian embryo remains an informative and powerful model system that has provided important insights into endothelial cell recruitment, assembly and remodeling during development of the circulatory system. This review highlights several discoveries in the avian system that show how arterial patterning is regulated using the model of dorsal aortae development along the embryo midline during gastrulation and neurulation. These discoveries were made possible through spatially and temporally controlled gain-of-function experiments that provided direct evidence that BMP signaling plays a pivotal role in vascular recruitment, patterning and remodeling and that Notch-signaling recruits vascular precursor cells to the dorsal aortae. Importantly, BMP ligands are broadly expressed throughout embryos but BMP signaling activation region is spatially defined by precisely regulated expression of BMP antagonists. These discoveries provide insight into how signaling, both positive and negative, regulate vascular patterning. This review also illustrates similarities of early arterial patterning along the embryonic midline in amniotes both avian and mammalians including human, evolutionarily specialized from non-amniotes such as fish and frog.