/sci/ - Science & Math

>>16165660
Are you Sarah Connor?

I'd go as a far as saying these kinds of threads are by far the most interesting ones here.

>>16148183
Genuine, novel.

due to sharing an ancestor that lived on the sea 660 million years ago

The degree of overall homology and the conservation of regulatory complexity between vertebrate and insect Hox complexes is simply amazing.

In posterior regions of the embryo, miR-196 is transcribed by promoter elements of paralog 10, processed, and bound to the 3′-untranslated region of Hox-8 mRNAs.

Hox-C8 mRNA and miR-196 have a single mismatch over the 22 nucleotide microRNA sequence, and binding triggers degradation by RNA interference (RNAi). More anterior mRNAs in Hox-7 and Hox-6 paralogous groups also bind to miR-196 but with more mismatches, causing translational inhibition instead of mRNA degradation.

This translational repression mechanism ensures that anterior Hox proteins are not translated posteriorly, explaining earlier observations that some mouse Hox proteins were not expressed in posterior regions of the embryo, whereas their transcripts were expressed all the way to the tip of the tail.

In the Bithorax gene complex of Drosophila, the infra-abdominal 4 (iab-4) gene is found at the equivalent location of miR-196. The iab-4 gene encodes a microRNA that binds to and inhibits Ultrabithorax mRNA translation and is expressed in abdominal segments; when miR-iab4 is overexpressed in the haltere it causes homeotic transformations into a wing.

In the Antennapedia complex a second microRNA, miR-10, has been mapped between Deformed and Sex combs reduced and at homologous positions in the mammalian Hox-B and Hox-D complexes.

Translational repression by microRNAs probably explains the enigmatic phenomenon of “posterior dominance” observed in Hox function.

Such an intricate machinery dedicated to specify identities along the A-P axis would, in all probability, not have evolved in the same way twice.

>For this reason, the inescapable conclusion is that a Hox complex was already functioning in Urbilateria (the ancestor of both human and insect).