Differential expression patterns of the hox gene are associated with differential growth of insect hind legs

Abstract

Diversification of leg appendages is one of the hallmarks of morphological evolution in insects. In particular, insect hind (T3) legs exhibit a whole spectrum of morphological diversification, ranging from uniform to extremely modified. To elucidate the developmental basis of T3 leg evolution, we have examined the expression patterns of two homeotic genes, Ultrabithorax and abdominal-A (collectively referred to as UbdA), in a broad range of species. First, our results show that UbdA expression in hemimetabolous insects is localized only in specific T3 leg segments undergoing differential growth (compared to their foreleg counterparts). In contrast, in basal hexapod and insect lineages, the absence of the UbdA signal coincides with uniform leg morphology. The same situation exists in first instar larvae of holometabolous insects, in which absence of UbdA expression in the embryonic T3 legs is associated with the lack of larval T3 leg diversification. Second, there is a clear difference in the timing of expression between species with greatly enlarged T3 leg, such as crickets and grasshoppers, and species that exhibit more moderate enlargement of hind legs, such as mantids and cockroaches. In the former, the UbdA expression starts much earlier, coinciding with the elongation of T3 limb buds. In the latter, however, the UbdA expression starts at much later stages of development, coinciding with the establishment of distinct leg segments. These results suggest that diversification of insect hind legs was influenced by changes in both the spatial and temporal regulation of the UbdA expression.

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

“…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.…”

Evolving expression patterns of the homeotic gene Scr in insects

“…Dissection and fixation of embryos was performed as previously described in Mahfooz et al (2004). Expression was detected by using a rat polyclonal antibody generated against a C-terminal fragment of Drosophila SCR and kindly donated by D.J.…”

“…1). The staining was performed as described in Mahfooz et al (2004). The antibody was detected by using a secondary anti-rat antibody that was conjugated to FITC, horseradish peroxidase, or alkaline phosphatase (The Jackson Laboratory).…”

“…The results obtained identified key changes in expression patterns of Ubx that directly correlated with changes in arthropod body plans Angelini and Kaufman, 2005;Averof and Patel, 1997;Castelli-Gair and Akam, 1995;Damen et al, 1998;Mahfooz et al, 2004;Peterson et al, 1999;Stern, 1998;Telford and Thomas, 1998;Zheng et al, 1999). In insects, Ubx expression has also been linked to the differential enlargement of insect hind (T3) legs, which were subsequently confirmed by functional studies (Mahfooz et al, 2007;Mahfooz et al, 2004). As illustrated by these findings, the availability of cross-reacting antibodies are critical in that they provide better phylogenetic sampling by circumventing the laborious process of cloning and characterizing orthologous genes.…”

“…Numerous studies have shown that changes in the expression and function of homeotic (hox) genes were pivotal in the evolution of the insect bauplan (Beeman et al, 1993;Beeman et al, 1989;Carroll et al, 2001;Hughes and Kaufman, 2000;Hughes and Kaufman, 2002;Mahfooz et al, 2007;Mahfooz et al, 2004;Rogers et al, 1997;Rogers et al, 2002;Struhl, 1982;Tomoyasu et al, 2005). This insight was primarily based on mRNA expression patterns, however, data on protein accumulation are much more limited.…”