Amplificador xenético: Diferenzas entre revisións

Algúns xenes implicdos en procesos fundamentais do desenvolvemento teñen moitos amplificadores de función solapada. Os amplificadores secundarios ou “amplificadores sombra” poden encontrarse a moitas quilobases de distancia desde o amplificador primario (“primario” refírese xeralmente ao primeiro amplificador descuberto, o cal normalmente está próximo ao xene que regula). Cada amplificador dirixe patrón case idénticos de [[expresión xénica]]. Algúns estudos trataron de ver se os dous amplificadores son verdadeiramente redundantes, e recentemente viuse que moitos amplificadores permiten que as moscas da froita sobreviva ás perturbacións ambientais, como un incremento de temperatura. Cando crecen a temperatura elevada, un só amplificados ás veces falla no seu control da patrón copleto de expresión, mentres que sa peesenza de os dous amplificadores permite a expresion niormal de xenes.<ref>{{cite journal |doi=10.1016/j.cub.2010.07.043 |title=Shadow Enhancers Foster Robustness of Drosophila Gastrulation |year=2010 |last1=Perry |first1=Michael W. |last2=Boettiger |first2=Alistair N. |last3=Bothma |first3=Jacques P. |last4=Levine |first4=Michael |journal=Current Biology |volume=20 |issue=17 |pages=1562–1567 |pmid=20797865}}</ref>

 

 

 

 

Recent work has investigated the role of enhancers in morphological changes in threespine [[stickleback]] fish. Sticklebacks exist in both marine and freshwater environments, but sticklebacks in many freshwater populations have completely lost their pelvic fins (appendages homologous to the posterior limb of tetrapods). ''[[Pitx1]]'' is a [[homeobox]] gene involved in posterior limb development in vertebrates. Preliminary genetic analyses indicated that changes in the expression of this gene were responsible for pelvic reduction in sticklebacks. Fish expressing only the freshwater [[allele]] of ''Pitx1'' do not have pelvic spines, whereas fish expressing a marine allele retain pelvic spines. A more thorough characterization showed that a 500 base pair enhancer sequence is responsible for turning on ''Pitx1'' expression in the posterior fin bud. This enhancer is located near a [[chromosomal fragile site]]--a sequence of DNA that is likely to be broken and thus more likely to be mutated as a result of imprecise [[DNA repair]]. This fragile site has caused repeated, independent losses of the enhancer responsible for driving ''Pitx1'' expression in the pelvic spines in isolated freshwater population, and without this enhancer, freshwater fish fail to develop pelvic spines.<ref>{{cite journal |doi=10.1126/science.1182213 |title=Adaptive Evolution of Pelvic Reduction in Sticklebacks by Recurrent Deletion of a Pitx1 Enhancer |year=2009 |last1=Chan |first1=Y. F. |last2=Marks |first2=M. E. |last3=Jones |first3=F. C. |last4=Villarreal |first4=G. |last5=Shapiro |first5=M. D. |last6=Brady |first6=S. D. |last7=Southwick |first7=A. M. |last8=Absher |first8=D. M. |last9=Grimwood |first9=J. |journal=Science |volume=327 |issue=5963 |pages=302–305 |pmid=20007865 |pmc=3109066}}</ref>