Pair-rule gene explained

A pair-rule gene is a type of gene involved in the development of the segmented embryos of insects. Pair-rule genes are expressed as a result of differing concentrations of gap gene proteins, which encode transcription factors controlling pair-rule gene expression.^{[1] [2]} Pair-rule genes are defined by the effect of a mutation in that gene, which causes the loss of the normal developmental pattern in alternating segments.

Pair-rule genes were first described by Christiane Nüsslein-Volhard and Eric Wieschaus in 1980.^[3] They used a genetic screen to identify genes required for embryonic development in the fruit fly Drosophila melanogaster. In normal unmutated Drosophila, each segment produces bristles called denticles in a band arranged on the side of the segment closer to the head (the anterior). They found five genes – even-skipped, hairy, odd-skipped, paired and runt – where mutations caused the deletion of a particular region of every alternate segment. For example, in even-skipped, the denticle bands of alternate segments are missing, which results in an embryo having half the number of denticle bands. Later work identified more pair-rule genes in the Drosophila early embryo – fushi tarazu, odd-paired and sloppy paired.^[4]

Once the pair-rule genes had been identified at the molecular level it was found that each gene is expressed in alternate parasegments – regions in the embryo that are closely related to segments, but are slightly out of register.^{[5] [6] [7] [8]} Each parasegment includes the posterior part of one (future) segment, and an anterior part of the next (more posterior) segment. The bands of expression of the pair-rule genes correspond to the regions missing in the mutant. The expression of the pair-rule genes in bands is dependent both upon direct regulation by the gap genes ^[9] and on regulatory interactions between the pair-rule genes themselves.^[10]

See also

• Drosophila embryogenesis
• Gap gene

External links

• The Interactive Fly: http://www.sdbonline.org/fly/aignfam/gapnprl.htm

Notes and References

1. Book: Gilbert. SF. Developmental Biology. 2000. Sinauer Associates. Sunderland (MA). The Origins of Anterior–Posterior Polarity. 6th. 23 October 2015.
2. Web site: Segmentation Genes in Drosophila Development: Pair Rule, Segment Polarity & Gap Genes. Study.com. 23 October 2015.
3. Nüsslein-Volhard C, Wieschaus E . Mutations affecting segment number and polarity in Drosophila . Nature . 287 . 5785 . 795–801 . October 1980 . 6776413 . 10.1038/287795a0. 1980Natur.287..795N . 4337658 .
4. Wakimoto BT, Kaufman TC . Analysis of larval segmentation in lethal genotypes associated with the antennapedia gene complex in Drosophila melanogaster . Dev. Biol. . 81 . 1 . 51–64 . January 1981 . 6780397 . 10.1016/0012-1606(81)90347-X.
5. Hafen E, Kuroiwa A, Gehring WJ . Spatial distribution of transcripts from the segmentation gene fushi tarazu during Drosophila embryonic development . Cell . 37 . 3 . 833–41 . July 1984 . 6430568 . 10.1016/0092-8674(84)90418-5. 37639734 .
6. Ingham, P. W. . K. R. Howard . D. Ish-Horowicz . amp . Transcription pattern of the Drosophila segmentation gene hairy . Nature . 318 . 6045 . 439–445 . 1985 . 10.1038/318439a0. 1985Natur.318..439I . 4302514 .
7. Macdonald PM, Ingham P, Struhl G . Isolation, structure, and expression of even-skipped: a second pair-rule gene of Drosophila containing a homeo box . Cell . 47 . 5 . 721–34 . December 1986 . 2877745 . 10.1016/0092-8674(86)90515-5. 39939403 .
8. Lawrence PA, Johnston P, Macdonald P, Struhl G . Borders of parasegments in Drosophila embryos are delimited by the fushi tarazu and even-skipped genes . Nature . 328 . 6129 . 440–2 . 1987 . 2886916 . 10.1038/328440a0 . 5929386 .
9. Ingham, P. W. . Ish-Horowicz, D. . Howard, KR . amp . Correlative changes in homoeotic and segmentation gene expression in Krüppel mutant embryos of Drosophila . The EMBO Journal . 5 . 7 . 1659–65. 1986. 10.1002/j.1460-2075.1986.tb04409.x . 16453692 . 1166992 .
10. Howard K . . Ingham P . amp . Regulatory interactions between the segmentation genes fushi tarazu, hairy, and engrailed in the Drosophila blastoderm . Cell . 44 . 6 . 949–957 . 10.1016/0092-8674(86)90018-8. 1986 . 3955654 . 28770534 .