Differential Axial Requirements for Lunatic Fringe and Hes7 Transcription during Mouse Somitogenesis
Figure 1
Expressing transgenic cLfng in the cranial PSM stripe.
(A) Constructs BB-cLfng and Lfng5kb-cLfng were used to generate transgenic lines BBL-1/-2 and 5kL-1/-2, respectively. cLfng ORF (orange) is under the control of either a duplication of the stripe-specific B-block enhancer and the β-globin basic promoter P (top), or 5 kb of the mouse Lfng promoter containing conserved cis-regulatory elements A-, B-, C-blocks (bottom; [15]). (B) The resulting transgenic expression (visualised by in situ hybridization with a cLfng probe on PSMs of hemizygous E10.5 embryos of lines BBL-1, BBL-2, 5kL-1 and 5kL-2) is confined to the cranial PSM stripe in BBL embryos or comprises stripe plus oscillatory domain in 5kL embryos. Position of PSM, somitomeres s-I and s0 and somites sI and sII are indicated on the left. Note the different expression levels, as reflected by the different times of colour development (in hours) given at the bottom of each panel. (C–F) Extended time of colour development does not detect endogenous Lfng expression in wildtype, but unexpected weak and dynamic cLfng expression in the caudal and mid-PSM of BBL embryos (white arrowheads). (G–I) Transgenic cLfng is expressed in the PSM (boxed in C–I) at all stages of segmentation (e.g. G–G″: hemizygous BBL-1 embryos at embryonic day E8.5, E10.5 and E12.5) and in ectopic expression domains outside the PSM (e.g. H, I: 5kL-1 and 5kL-2; black arrows and arrowheads). Arrowed domains are seen in all transgenic lines, indicating that the Lfng promoter includes repressive regulatory elements that lie outside the proximal 5 kb region.