The function of Hox and appendage-patterning genes in the development of an evolutionary novelty, thePhoturisfirefly lantern

Abstract

Uncovering the mechanisms underlying the evolution of novel traits is a central challenge in biology. The lanterns of fireflies are complex traits that lack even remote homology to structures outside luminescent beetle families. Representing unambiguous novelties by the strictest definition, their developmental underpinnings may provide clues to their origin and offer insights into the mechanisms of innovation in developmental evolution. Lanterns develop within the context of abdominal Hox expression domains, and we hypothesized that lantern formation may be instructed in part by these highly conserved transcription factors. We show that transcript depletion of Abdominal-B in Photuris fireflies results in extensive disruption of the adult lantern, suggesting that the evolution of adult lanterns involved the acquisition of a novel regulatory role for this Hox gene. Using the same approach, we show that the Hox gene abdominal-A may control important secondary aspects of lantern development. Lastly, we hypothesized that lantern evolution may have involved the recruitment of dormant abdominal appendage-patterning domains; however, transcript depletion of two genes, Distal-less and dachshund, suggests that they do not contribute to lantern development. Our results suggest that complex novelties can arise within the confines of ancestral regulatory landscapes through acquisition of novel targets without compromising ancestral functions.

Hexapoda: Comparative Aspects of Later Embryogenesis and Metamorphosis

“…In Drosophila , the genital imaginal disc shows limited co-expression of Dll and Abd -B , and Abd -B represses Dll expression and regulates imaginal disc identity (Estrada and Sánchez-Herrero 2001 ;Foronda et al 2006 ). At metamorphosis, loss of Abd -B leads to transformation of genitalia into legs in Drosophila (Estrada and Sánchez-Herrero 2001 ) and the beetle Photuris (Stansbury and Moczek 2014 ). Such transformations have not been reported in Tribolium or Oncopeltus , and in the latter, Abd -B activates, rather than represses, Dll in the genital disc (Aspiras et al 2011 ).…”

“…Ubx , abd -A , and Abd -B combinatorially specify segment identities in the abdomen, in part by repressing or regulating appendage identities (see below). Abd -B and abd -A both play roles in specifi cation and patterning of genitalia (Estrada and Sánchez-Herrero 2001 ;Chen et al 2005 ;Aspiras et al 2011 ;Stansbury and Moczek 2014 ).…”

Evolutionary Developmental Biology of Invertebrates 5

“…The anterior expression boundary of abd -A varies across species but does not reach the anterior end of the abdomen (Regulski et al 1985 ;Peterson et al 1999 ;Angelini et al 2005 ;Zhang et al 2005 ;Konopova and Akam 2014 ). Abd -B and abd -A both play roles in specifi cation and patterning of genitalia (Estrada and Sánchez-Herrero 2001 ;Chen et al 2005 ;Aspiras et al 2011 ;Stansbury and Moczek 2014 ). Abd -B expression extends from an anterior boundary within the abd -A domain to the posterior-most region of the abdomen (Regulski et al 1985 ;Kelsh et al 1993 ;Peterson et al 1999 ;Angelini et al 2005 ).…”

A expressão dos Genes HOX e a má formação da coluna vertebral

“…23 Padrões do gene HOM-C Ultrabithorax (Ubx) de expressão estão associados com o aumento diferencial de determinados segmentos membros pélvicos em diferentes espécies. 26,28 Estudos identificaram vários papéis importantes para os genes HOX no desenvolvimento de órgãos que correspondem à sua expressão ao longo do eixo A-P. O uso de animais transgênicos com ganho ou perda de funções genicas tem nos respondido diversas questões importantes. Em camundongo e provavelmente em humanos, utiliza-se a teoria de redundância.…”

“…Animais que possuem a expressão desses genes normais não possuem qualquer problema, já indivíduos sem a expressão apresentam uma intensa hipoplasia durante a prenhez e lactação. 27,28,30 Em uma análise especifica do Clusters B (HOXB2-HOXB6) durante o desenvolvimento pulmonar de camundongos na embriogênese foi demonstrado que os genes HOXB3 e HOXB4 induzem à formação da região cranial (Traqueia e Brônquio principal), enquanto que os genes HOXB2 e HOXB5 a região caudal 30 . Em uma análise subsequente, foi constatado que no pulmão adulto, 11 membros da família HOX fazem a manutenção da hemostasia dos tecidos clusters A (HOXA2-HOXA6), Clusters B (HOXB2-HOXB6) e o gene HOXD.…”