Studies on Aedes and Anopheles mosquitoes at the molecular level of genetics
Section 1: Construction and screening of a genomic library for the
mosquito Aedes aegypti (Diptera, culicidae).
A genomic library has been constructed for this important vector
of arboviral disease. Total genomic DNA and various classes of RNA
from Ae. aegypti were used to screen this library. The results
obtained indicate that this species has a short period interspersion
pattern of repeated sequences. Transcription of these repeats could
not be detected using total cytoplasmic RNA, hnRNA or mRNA as
Section 2: Sequence organisation of ribosomal DNA in Aedes aegypti.
The Aedes aegypti genomic library was used to isolate clones
containing the intact ribosomal DNA (rDNA) repeat of this species.
This has been restriction mapped and the transcribed regions have been
identified. The rDNA repeat is 9.0 Kb in length and is present as
approximately 500 head-to-tail tandemly repeated copies. A low level
of intraspecies polymorphism of Ae. aegypti rDNA is evident. Two
restriction polymorphisms have been identified within the rDNA repeat.
Section 3: Analysis of ribosomal DNA variation within Ae. aegypti'and
between closely related species.
Four variant rDNA clones have been isolated. One of these' may
contain the end of a tandem array of ribosomal genes. Another variant
contains a duplication of rDNA within the internal transcribed spacer
region of the ribosomal repeat. Sequence analysis of this clone has
identified regions at the 3' end of the 18S rRNA gene of Ae. aegypti
which show very strong homology with the corresponding regions in
other species. Some repeated sequences have been identified
downstream of the 18S rRNA gene in this clone. Preliminary analysis
of the two other rDNA variants indicates that one contains a
duplication or insertion of DNA in the 28S rRNA coding region and one
contains non-transcribed spacer homologous sequences which are not
associated with rRNA coding regions.
Section 4: DNA probes for species identification of mosquitoes in the
Anopheles gambiae complex.
DNA sequences have been isolated which distinguish four of the
morphologically identical members of the An. gambiae species complex.
Two sequence classes were obtained. Class 1 homologues are highly
reiterated in the genomes of An. arabiensis and An. merus, present in
low copy number in An. melas and were not detected in An. gambiae s. s.
Class 1 sequences are male specific in An. arabiensis. Class 2
homologues are highly reiterated in the genomes of An. merus and An.
melas and present in low to middle copy number in An. gambiae s. s, and
An. arabiensis. Sex specificity of Class 2 homologues does not occur
in the species tested (An. gambiae s. s. and An. arabiensis).
Hybridisation of these species specific DNA sequences to mosquitoes
squashed directly onto nitrocellulose provides a simplified method of