Homeotic gene expression in the locust<i>Schistocerca</i>: An antibody that detects conserved epitopes in ultrabithorax and abdominal‐A proteins

102

103

Crustaceans possess remarkably diverse appendages, both between segments of a single individual as well as between species. Previous studies in a wide range of crustaceans have demonstrated a correlation between the anterior expression boundary of the homeotic (Hox) gene Ultrabithorax (Ubx) and the location and number of specialized thoracic feeding appendages, called maxillipeds. Given that Hox genes regulate regional identity in organisms as diverse as mice and flies, these observations in crustaceans led to the hypothesis that Ubx expression regulates the number of maxillipeds and that evolutionary changes in Ubx expression have generated various aspects of crustacean appendage diversity. Specifically, evolutionary changes in the expression boundary of Ubx have resulted in crustacean species with either 0, 1, 2, or 3 pairs of thoracic maxillipeds. Here we test this hypothesis by altering the expression of Ubx in Parhyale hawaiensis, a crustacean that normally possesses a single pair of maxillipeds. By reducing Ubx expression, we can generate Parhyale with additional maxillipeds in a pattern reminiscent of that seen in other crustacean species, and these morphological alterations are maintained as the animals molt and mature. These results provide critical evidence supporting the proposition that changes in Ubx expression have played a role in generating crustacean appendage diversity and lend general insights into the mechanisms of morphological evolution.appendages ͉ arthropods ͉ development ͉ Hox

Section: Methodsmentioning

confidence: 99%

Knockdown of Parhyale Ultrabithorax recapitulates evolutionary changes in crustacean appendage morphology

Liubicich

Serano

Pavlopoulos³

et al. 2009

102

103

“…Immunochemical stainings in Artemia were carried out using specific polyclonal antibodies for Caudal and Eve (20), the monoclonal antibody 4F11 for En (26), and the monoclonal antibody FP6.87 for Ubx͞AbdA (27). Whole-mount immunochemical stainings were carried out according to standard protocols (28), with sonication of varying strengths, depending on the developmental stage.…”

Section: Methodsmentioning

confidence: 99%

Ancestral role of caudal genes in axis elongation and segmentation

Copf

Schröder

Averof

2004

178

170

caudal (cad͞Cdx) genes are essential for the formation of posterior structures in Drosophila, Caenorhabditis elegans, and vertebrates. In contrast to Drosophila, the majority of arthropods generate their segments sequentially from a posteriorly located growth zone, a process known as short-germ development. caudal homologues are expressed in the growth zone of diverse short-germ arthropods, but until now their functional role in these animals had not been studied. Here, we use RNA interference to examine the function of caudal genes in two short-germ arthropods, the crustacean Artemia franciscana and the beetle Tribolium castaneum. We show that, in both species, caudal is required for the formation of most body segments. In animals with reduced levels of caudal expression, axis elongation stops, resulting in severe truncations that remove most trunk segments. We also show that caudal function is required for the early phases of segmentation and Hox gene expression. The observed phenotypes suggest that in arthropods caudal had an ancestral role in axis elongation and segmentation, and was required for the formation of most body segments. Similarities to the function of vertebrate Cdx genes in the presomitic mesoderm, from which somites are generated, indicate that this role may also predate the origin of the Bilateria.caudal͞Cdx genes ͉ short-germ development ͉ Artemia ͉ Tribolium ͉ evolution T he caudal (cad͞Cdx) genes are homeobox genes involved in posterior patterning in diverse species (1-11). In early Drosophila embryos Caudal protein is distributed in a posterior to anterior concentration gradient that is needed for the activation of segmentation genes and segment formation in posterior parts of the animal. caudal mutant embryos have severe segmentation problems affecting posterior segments; in the most severely affected mutants, most abdominal segments are missing (1). This function of caudal is characteristic of long-germ development, found in Drosophila, where all of the body segments are molecularly determined during the blastoderm stage. This mode is thought to be evolutionarily derived within the higher insects and does not represent the ancestral mode of development (12). On the contrary, short-germ development is found in diverse and phylogenetically basal groups of insects and other arthropods, suggesting that this represents the ancestral mode for generating segments within the arthropods. In short-germ arthropods (which we take to include intermediate-germ species), only the most anterior segments are laid down in the blastoderm (e.g., Fig. 1A), whereas more posterior segments are generated sequentially from a posteriorly located presegmental zone, usually referred to as the ''growth zone '' (12-14). caudal homologues have been cloned in some short-germ arthropods and found to be expressed consistently in this presegmental zone (15-22), but until now their function in these species had not been studied.To explore the functional role of caudal genes in the growth zone of short-germ arthropods, we ...

“…In addition, a recent study of related Drosophila species shows that differential Ubx expression is directly regulating the fine-scale morphological differences (such as bristle pattern) between T3 and T2 legs (12). Interestingly, the putative role of Ubx in the evolution of grasshopper hind legs has also been postulated on the basis of its expression pattern in this species (13). These results prompted us to hypothesize that instead of being restricted to only a couple of species, Ubx may actually play a role in diversification of insect hinds legs in general.…”

mentioning

confidence: 99%

“…To detect Ubx expression in the hind leg, we use the crossreacting mouse monoclonal antibody FP6.87 (13). This antibody recognizes both the Ubx protein and that of the second abdominal homeotic regulator abdominal-A (abd-A) in a wide range of arthropod species (13)(14)(15)(16)(17).…”

mentioning

confidence: 99%

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

Mahfooz

Popadić

2004

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.