Carmichael’s Concise Review
the window, and the window was secured in position with glue. Tis minimized motion from the dam’s breathing. Te initial window was circular with a 10 mm inner diameter and 1.5 mm depth. It was replaced with a larger, elliptical window (long axis 15 mm) during the later stages. Te window was covered with a glass cover slip that could be removed for manipulating the embryo. For the early stages the decidua and uterine muscle were
stripped to improve visualization of the embryo. Aſter E12.5 the decidua diminished, and the uterine wall became trans- parent, so there was no need for the stripping procedure. Tese procedures did not interfere with embryo survival in most cases as indicated by a beating heart. Later histological examination using hematoxylin and eosin staining showed no structural abnormalities in the embryos underneath the win- dow. Aſter the pups were born they suckled normally, and pups imaged as embryos under the window were indistinguishable from their littermates. Tey grew normally without noticeable abnormalities. Transgenic mice with cell lineage-specific expression of
fluorescent reporter are commonly used to study develop- ment in live organisms. Huang et al. used stereoscopic and two-photon microscopy to observe embryos in transgenic (for example, Wnt1-Cre-tdTomato) mice. Tey conducted a series of studies that not only provided proof of concept for the use of these windows, but also resulted in important information about embryogenesis. Briefly, the studies observed transient neurotransmission and early vasculatization neural crest cell (NCC)-derived perivascular cells in the brain, autophagy in the retina, viral gene delivery, and chemical diffusion through the placenta (Figure 1). Tey combined the imaging window with increasing the permeability of plasma membranes using an electrical field (electroporation) to label and track cell divi- sion and movement within embryos in utero. In addition, they observed that clusters of mouse NCC-derived cells expanded in interspecies chimeras, whereas adjacent human donor NCC-derived cells shrank. Huang et al. have developed an intravital imaging win-
dow for visualizing and manipulating live mouse embryos in vivo from E9.5 until birth (around E20). Tis elegant study demonstrates the capability to image whole embryos in utero at high resolution, opening many new avenues for investiga- tion: brain formation, peripheral nerve development, placen- tal development, birth defects, gene editing, development of the immune system, environmental effects, and interspecies chimeras. It will be fascinating to see what new discover- ies in embryogenesis are revealed using this exciting new technique!
References [1] Huang et al., Science 368 (2020) 181–86. [2] Te author gratefully acknowledges Drs. Qiang Huang, Rudolf Jaenisch, and Xiling Shen for reviewing this article.
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