Fig. 2

Expression pattern analysis of her15 in the caudal PSM. Expression of her15 was analysed from 70% epiboly up to 16-somite stage focusing on the caudal PSM. Expression first appears during epiboly at the epibolic margin while the dorsal midline is devoid of transcript (A and B). Note expression on either side of the dorsal midline extents during epiboly towards the anterior pole (white arrow). At bud an expression domain is observed posterior to the notochord, which shows different width in a batch of embryos of nearly the same developmental stage (C–F). Due to narrowing and lengthening of the tail bud only broad and dot-like expression can unambiguously be distinguished in 12- to 14- (G and H, respectively) or 16- to 18-somite stage embryos (I and J, respectively; K and L are magnifications of the tail bud in panels I and J). During these stages it also becomes evident that the staining in the dot-like expression phase extends from ventral to dorsal in the midline of the tail bud (H and J). Wt embryos at the 10- to 12-somite stage were double-stained for her7 transcripts (red) and her15 (M, N) or her12 (O, P) transcripts (blue). “Broad” staining patterns for her15 and her12 coincided with ubiquitous her7 expression in the posterior PSM (M, O), “dot-like” her15 and her12 patterns were associated with low her7 staining in the this region (N, P). Arrowhead in panel P points to a region in the caudal PSM with her12 transcription only, indicating slight phase shifts to her7.