Ultrasound Backscatter Microscopy of Mouse Embryos

Extensive genetic information and transgenic techniques available in the mouse have led to its wide use in studies of mammalian development and models of human disease. A basic limitation of analyzing dynamic developmental processes in mouse embryos is their inaccessibility, because they are encased in the maternal uterus. In particular, cardiovascular development has been difficult to study and an understanding of the underlying mechanisms regulating heart development is incomplete, in part because of the lack of methods to measure cardio- and hemodynamics in live mouse embryos. Also, in contrast to lower vertebrate species such as frog, chick, and zebrafish, direct in utero manipulation of mouse embryos, through injection of dyes, cells, or retroviruses are difficult or impossible at most embryonic stages. High-frequency (40–50 MHz) ultrasound imaging and Doppler scanners, also called ultrasound backscatter microscopes (UBM), have recently been developed that allow noninvasive measurements of cardiovascular structure and function in live mouse embryos and that make possible direct in utero manipulations through high-resolution ultrasound-guided injections. This protocol describes methods that have been employed to image and measure blood flow in live mouse embryos and to inject cells, retroviruses and other agents into specific embryonic target sites using UBM imaging as a guidance system.