They, too, noticed that the same Sonic hedgehog enhancer had many deletions and mutations.
And it's possible that the Sonic hedgehog enhancer was not the first step in leg loss, Hanken says.
They then showed that a mutated Sonic hedgehog enhancer does indeed affect leg growth by testing its influence on mouse limbs.
EMID2 is linked to a sonic hedgehog (SHH) enhancer adoption mutation, where an EMID2 enhancer drives ectopic SHH expression (Lettice et al. 2011), although the loci identified are not located within that enhancer element.
As a proof of principle, we first injected oocytes with a vector containing the well-characterized Sonic hedghehog limb enhancer [3], and performed LacZ staining on E11 embryos.
Cis-regulatory domains can extend long distances outside the transcription unit; an enhancer for Sonic Hedghog for example is located one megabase away from its target gene [3].
The Sonic Hedgehog (SHH) limb enhancer is approximately 1,000,000 bp away from its TSS, highlighting the difficulty in linking such elements with a target gene [ 37].
Considering observations with other developmental genes in gene poor regions, such as sonic hedgehog (SHH) [30], enhancers could even map within or beyond the neighbouring genes.
A locus for triphalangeal thumb, variably associated with pre-axial polydactyly, was previously identified in the zone of polarizing activity regulatory sequence (ZRS), a long range limb-specific enhancer of the Sonic Hedgehog (SHH) gene at human chromosome 7q36.3.
Selected genes included wnt10a, axin2a, fibroblast growth factor 20a (fibroblastibroblast growth factor receptor 1 (fgf1), muscle segment homeobox b (msxb), retinaldehyde dehydrogenase 2 (raldh2), sonic hedgehog (shh) and lymphoid enhancer-binding factor 1 (lef1).
L. menadoensis has also been the subject of other molecular investigations aimed at characterizing some genes of evolutionary interest: Hox genes [ 21- 23], ParaHox genes [ 24], the Protocadherine cluster [ 25], the RAG1 and RAG2 genes [ 11], Sonic hedgehog gene and its enhancers [ 26], visual pigments [ 27], a Heat Shock Protein 70[ 28], neurohypophysial hormones [ 29], and vitellogenins [ 30].
