The Chromosomes of Zeugodacus tau and Zeugodacus cucurbitae: A Comparative Analysis

Availability of polytene chromosomes and development of polytene chromosome maps have greatly facilitated genetic analysis in Diptera and understanding of chromosomal organization. In tephritids, following the first polytene chromosome maps constructed for the Mediterranean fruit fly, Ceratitis capitata, additional maps have been developed for only few species belonging to the main genera of agricultural importance that are Anastrepha, Bactrocera, Ceratitis, Dacus, Rhagoletis, and Zeugodacus. Comparison of the polytene chromosomes of these species has pointed to the presence of chromosomal rearrangements that can, at least partially, shed light to the chromosomal evolution in this family. Up to now, polytene chromosome maps are available only for one Zeugodacus species, that is Zeugodacus cucurbitae. Here we report the cytogenetic analysis of the mitotic and polytene chromosomes of the pumpkin fly, Zeugodacus tau, along with a comparative analysis with polytene chromosomes of Zeugodacus cucurbitae as well as other tephritids. In situ hybridization experiments resulting to chromosomal localization of selected genes in both species are also presented. The genes used as markers are hsp70, hsp83, scarlet and white pupae. The established homologies presented in this study verify that the two Zeugodacus species are genetically close and support the current taxonomic placement of the Zeugodacus genus. The differences in polytene chromosome level, in combination with results of in situ hybridization experiments, reveal the presence of chromosomal rearrangements, mainly inversions, to both closely and distantly related species, which could potentially be a useful diagnostic tool.

Polytene chromosome maps in four species of tsetse flies Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans (Diptera: Glossinidae): a comparative analysis

Photographic polytene chromosome maps from pupal trichogen cells of four tsetse species, Glossina austeni, G. pallidipes, G. morsitans morsitans and G. m. submorsitans were constructed and compared. The homology of chromosomal elements between the species was achieved by comparing banding patterns. The telomeric and subtelomeric chromosome regions were found to be identical in all species. The pericentromeric regions were found to be similar in the X chromosome and the left arm of L1 chromosome (L1L) but different in L2 chromosome and the right arm of L1 chromosome (L1R). The L2 chromosome differs by a pericentric inversion that is fixed in the three species, G. pallidipes, G. morsitans morsitans and G. m. submorsitans. Moreover, the two morsitans subspecies appeared to be homosequential and differ only by two paracentric inversions on XL and L2L arm. Although a degree of similarity was observed across the homologous chromosomes in the four species, the relative position of specific chromosome regions was different due to chromosome inversions established during their phylogeny. However, there are regions that show no apparent homology between the species, an observation that may be attributed to the considerable intra--chromosomal rearrangements that have occurred following the species divergence. The results of this comparative analysis support the current phylogenetic relationships of the genus Glossina.

Identification and partial characterization of a new Ceratitis capitata-specific 44-bp pericentromeric repeat

Tandem satellite DNA repeats are often associated with centromeres. In spite of their importance in the organization of the centromere, they do not seem to be broadly conserved among species and their role is still unclear. Here we report the identification of a new 44-bp tandem pericentromeric repeat from the medfly, Ceratitis capitata. The repeat is specific to this insect and is not found in any of the other closely related species tested. It localizes in four out of its five autosomes and in the X chromosome. It is organized in long arrays, interspersed by transposable elements and other less well-defined sequence motifs.

Photographic polytene chromosome maps for Glossina morsitans submorsitans (Diptera: Glossinidae): cytogenetic analysis of a colony with sex-ratio distortion

Photographic polytene chromosome maps from trichogen cells of pharate adult Glossina morsitans submorsitans were constructed. Using the standard system employed to map polytene chromosomes of Drosophila, the characteristic landmarks were described for the X chromosome and the two autosomes (L1 and L2). Sex-ratio distortion, which is expressed in male G. m. submorsitans, was found to be associated with an X chromosome (X8) that contains three inversions in each arm. Preliminary data indicate no differences in the fecundity of X(A)X(A) and X(A)X(B) females, but there are indications that G. m. submorsitans in colonies originating from Burkina Faso and Nigeria have genes on the autosomes and (or) the Y chromosome that suppress expression of sex-ratio distortion.

Ecdysone-regulated chromosome puffing in the salivary glands of the Mediterranean fruit fly, Ceratitis capitata

The effect of ecdysone on the puffing activity of the polytene chromosomes of Ceratitis capitata has been studied in organ cultures of late-larval salivary glands. Culture of glands from 120-h-old larvae (puff stage 1) in the presence of ecdysone resulted in the initiation of the late-larval puffing cycle that is normally observed in 145-h-old larvae (puff stage 4). During a 7-h period in the presence of ecdysone, the puffing patterns of most loci resembled the in vivo patterns observed in the period between puff stages 4 and 10, indicating that the first puffing cycle can be initiated by the hormone and proceed almost to completion, in vitro. Culture of salivary glands in the presence of ecdysone and a protein-synthesis inhibitor, as well as ecdysone withdrawal and readdition experiments, indicated that most of the ecdysone-regulated puffs could be categorized into three classes: (i) the puffs that were suppressed immediately by ecdysone, even in the absence of protein synthesis; (ii) the puffs that were induced directly by ecdysone; and (iii) the puffs that were induced indirectly by ecdysone, that is, they were induced after a lag period of a few hours and required protein synthesis for their induction.

Hermes-mediated germ-line transformation of the Mediterranean fruit fly Ceratitis capitata

We report the use of the Hermes transposable element for germ-line transformation of the Mediterranean fruit fly, Ceratitis capitata. Hermes was able to genetically transform this insect at an estimated frequency between 0.6 and 1.1%, which is comparable to the transformation frequencies obtained for this species when using other transposable elements. Hermes integrates into the medfly genome by a cut-and-paste mechanism and the sequences integrated into the genome are delimited by the terminal nucleotides of the Hermes inverted terminal repeats. Integration resulted in the generation of 8 bp target site duplications, the sequences of which conformed to the target site duplications generated by hAT element transposition in insects. The Hermes element is one additional genetic tool that can be deployed in manipulating and characterizing the medfly genome.