Dissection embryos, mouse

Dissect one mouse at a time so that the embryos are placed in fix (FPBS) as soon as possible It is important to avoid bruising or otherwise damaging the embryos during the dissection... 

Sacrifice a pregnant mouse (about 15 d postcoitus), moisten the belly with 70% ethanol, remove the uterus and place it in a 10-mm Petri dish containing phosphate-buffered saline (PBS). Dissect the embryos away from the uterus and membranes, and transfer them into a new dish containing PBS. 

Downs, K. and Davies, T. (1993) Staging of gastrulating mouse embryos by morphological landmarks in the dissecting microscope. Development 118, 1255-1266. 

Dissect out embryos in ice-cold PBS (mouse, chick) or Howard s Ringer (chick) and open cavities. 

This protocol works well on intact embryos up to at least mouse embryonic d 12, chick Hamburger and Hamilton (3) stage 24, and zebrafish to 72h (see also Note 7 for zebrafish modifications). For older embryos, it is likely that some block dissection is required prior to fixation to keep background levels low. Alternatively, some tissues, such as the neural tube, can be dissected after performing the procedure on intact older embryos. 

Dissect out the embryos into an appropriate physiological salt solution, such as PBS, for mouse embryos or Howard s Ringer for chick embryos, and process directly. 

Figure L Explant culture assays for gastrulation stage mouse embryos, (A) Photograph of mid-streak embryo, a, anterior p, posterior w, mesoderm ps, region of primitive streak. (B) Photograph of mid-streak embryo (arrow) at tip ofpencil to provide indication of size, (C) Diagram of induction assay, (D) Diatom indicating anterior ectoderm region of mid-streak embryo dissected for reprogramming assay.

Fixation times might be reduced for very small embryos. Young mouse embryos, if left inside the decidua, can be fixed overnight safely. Fixation can be reduced to 2-4 h for embryos that are dissected out, although overnight fixation is not obviously detrimental. Chick embryos below stage 17, however, should be fixed only for 2 h (S Smith, personal communication). 

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