PEST

The Anopheles gambiae PEST strain was chosen for genome sequencing because it had both a fixed, standard chromosomal arrangement and a sex-linked pink eye mutation that could readily be used as an indicator of cross-colony contamination (Holt et al 2002: PMID 12364791). The pink eye mutation originated in a colony called A. gambiae LPE established in 1951 at the London School of Hygiene and Tropical Medicine from mosquitoes collected in Lagos, Nigeria. In 1986, this mutation was introduced into a colony of A. gambiae from Asembo Bay western Kenya by crossing males of the LPE strain with female offspring of wild caught Kenyan A. gambiae (the Savanna form), selecting males from the F2 of this cross and then crossing them again with additional female offspring of wild caught Kenyan A. gambiae. From the F2 offspring of this second outcross to Kenyan mosquitoes, a strain was selected that was fixed for pink eye. This outcrossing scheme was repeated one more time in 1987 producing a pink eye strain with a genetic composition largely constituted of the western Kenya Savanna cytogenetic form. In each of these crosses, several hundred female offspring of at least 20 wild caught mosquitoes were used in the cross. This strain, designated A. gambiae PE (Pink Eye), was polymorphic for the inversions 2La (32%) and 2Rbc (19%). The 2Rbc inversion is characteristic of the Mopti chromosomal form, indicating that the original LPE strain from Nigeria was the Mopti form, which is the M molecular form. This inversion was apparently balanced by the uninverted form, because no 2Rbc/bc individuals were detected in the colony. Mukabayire and Besansky selected from this PE strain a set of 9 families whose female parent and at least 20 female offspring were fixed for the standard chromosome karyotype. The progeny of these nine families were pooled to form the A. gambiae PEST strain (Pink Eye STandard). This strain clearly had some Mopti-derived DNA, as the standard karyotype is shared by Mopti and Savanna and the original PE strain did have the 2Rbc inversion rather than 2Rb that is typical of Savanna. Clones from two different PEST strain BAC (Bacterial Artificial Chromosome) libraries had already been end sequenced and physically mapped. When tested, this colony was fully susceptible to P. falciparum from western Kenya. DNA preparation and library construction methods were conducted following standard protocols, and the sequencing method was whole-genome Sanger sequencing. Subsequent to sequencing, the PEST strain was found to be polymorphic for molecular markers diagnostic of the A. gambiae M and S molecular forms. The last known isolate of the A. gambiae PEST colony was lost in about 2005.

Organism: 
Anopheles gambiae

Anopheles gambiae senso stricto is the primary mosquito vector responsible for the transmission of malaria in most of sub-Saharan Africa. It is a member of a species complex that includes at least seven morphologically indistinguishable species in the Series Pyretophorus in the Anopheles subgenus Cellia. Anopheles gambiae feeds preferentially on humans and is one of the most efficient malaria vectors known.

Genome assemblies and gene sets