Table 1. Staging criteria for assignment of embryos to particular timepoints and corresponding RNA yields. TS  =  Theiler stage.

Timepoint	Staging Criteria	Number of embryos needed for >5 µg total RNA from each prominence
E10.5	TS 17 (lens vesicles form deep pockets)	24–28
E11.0	TS 18 (three hyoid auricular hillocks)	8–9
E11.5	TS19 (nares narrow to small slits)	8–9
E12.0	TS 20.1 (tongue begins to form)	3–4
E12.5	TS 20.3 (mandibular arch and the first hyoid auricular hillock begin to fuse)	3–4