evx1 and prdm1 expression in the cloaca of Hh pathway mutant embryos. (A-D, M-O) WT sibling, 24-120 hpf. At 24 hpf evx1 and prdm1 are expressed in the proctodeum and caudal pronephros. They may also be expressed in the posterior gut at this stage, but it is difficult to determine the presence of endoderm in this area at 24hpf. Expression marked by the arrow may be the proctodeal tissue that fuses with the gastrointestinal tract. Expression in the proctodeum/cloaca is maintained until at least 120hpf. (E-F, P-R) smu, 24-120hpf. Despite morphological changes to the proctodeum and cloaca expression of evx1 and prdm1 are maintained. The altered shape of the expression domain appears to reflect the change in shape of the cloaca seen in live embryos but not a loss of the tissue itself. At 24 hpf–prdm1 expression is not detectable in the putative posterior gut (arrow) whereas evx1 expression is normal. Prdm1 expression in the epidermis persists past 24 hpf in smu mutants (asterix) but not in WT siblings, suggesting that prdm1 is regulated by Hh activity in the epidermis, but not the procotdeum. (I-L, S-U) syu, 24-120hpf. Expression of“evx1 and prdm1 are maintained in the cloaca of syu mutants. At 24hpf the expression of evx1 appears to be weaker than the WT siblings, but at other time points is barely distinguishable from the siblings, whilst prdm1 expression at 24 hpf is normal in syu. Like smu mutants prdm1 expression in the epidermis persists past 24 hpf (asterix).
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