Extended Data Fig. 2: Lowering the pHi can reversibly slow down embryo elongation.

a, b, Snapshots of 2-day-old chicken embryos cultured in minimal medium at pH 7.2 with 8.3 mM (n = 6) glucose (a) or 0.83 mM glucose (n = 3) (b). c, d, Snapshots of 2-day-old chicken embryos cultured in minimal medium with 8.3 mM glucose in acidic conditions (pH 6.0: n = 6 (c) and pH 5.3: n = 6 (d)). e, Snapshots of a 2-day-old chicken embryo first cultured in minimal medium with 8.3 mM glucose at pH 5.3 showing the arrest of elongation after 9 h, and returned to control medium after 10.5 h showing the rescue of elongation (n = 6). All panels show bright-field micrographs of the posterior region of chicken embryos taken at 1.5-h intervals. Somites formed at the last time point are indicated by asterisks on the right. The yellow asterisks mark the last somite at the beginning of the culture and the white asterisks are the somites produced during the culture period. The ventral views show the anterior region to the top. Scale bars, 100 μm.