Krüppel

Krüppel is a gap gene in Drosophila melanogaster, located on the 2R chromosome, which encodes a zinc finger C2H2 transcription factor.^[1][2] Gap genes work together to establish the anterior-posterior segment patterning of the insect through regulation of the transcription factor encoding pair rule genes. These genes in turn regulate segment polarity genes.^[3] Krüppel means "cripple" in German, named for the crippled appearance of mutant larvae, who have failed to develop proper thoracic and anterior segments in the abdominal region.^[4][5][6] Mutants can also have abdominal mirror duplications.

Krüppel
Identifiers
Organism	Drosophila melanogaster
Symbol	kr
UniProt	P07247
Search for Structures Swiss-model Domains InterPro

Krüppel homolog 1
Identifiers
Organism	Drosophila melanogaster
Symbol	kr-h1
UniProt	P08155
Search for Structures Swiss-model Domains InterPro

Krüppel homolog 2
Identifiers
Organism	Drosophila melanogaster
Symbol	kr-h2
UniProt	Q9V447
Search for Structures Swiss-model Domains InterPro

Krüppel-like factor luna
Identifiers
Organism	Drosophila melanogaster
Symbol	luna
UniProt	Q8MR37
Search for Structures Swiss-model Domains InterPro

In situ hybridization against mRNA of the gap genes knirps, Krüppel and giant in the Drosophila melanogaster early embryo. Panels also show how these genes are affected by the mutation brakeless (bks).

Human homologs of Krüppel are collectively named Krüppel-like factors, a set of proteins well characterized for their role in carcinogenesis.^{[7][8][9][10][11]}

Krüppel expression pathway

Krüppel is expressed in the center of the embryo during the cellular blastoderm stage of development.^[12] Its expression pattern is restricted to this domain largely through interactions with the maternal effect genes Bicoid and Nanos, and fellow gap gene Hunchback and Knirps.^[13]

Bicoid maternal transcripts are deposited at the anterior end of the embryo, while Nanos maternal transcripts are located at the posterior. Hunchback mRNA transcripts are present throughout the embryo. Bicoid and Nanos both encode morphogens that have the opposite effect on Hunchback mRNA translation – Bicoid activates translation, whereas Nanos represses it.^[14] As such, Hunchback mRNA is translated so that Hunchback protein is present in the concentration gradient which decreases along the anterior – posterior axis. This Hunchback gradient indirectly results in an anterior boundary for Knirps expression. Other factors induce a posterior boundary, so that Knirps is expressed in a stripe in the posterior region of the embryo.

Hunchback and Knirps are both transcription factors that regulate Krüppel expression. High levels of Hunchback inhibit expression, whereas low levels of Hunchback activate expression. Knirps acts as a repressor to inhibit expression. This results in Krüppel being expressed in a stripe in the center of the embryo's A-P axis, where Hunchback concentration has dropped to a low enough level so that it can act as an activator, but Knirps is not yet present to inhibit. In this way the initial gradients of morphogens can lead to the establishment of a specific region within the blastoderm. It can be compared to a narrow bandwidth filter in engineering.

Effects of Krüppel expression

The Krüppel protein is a transcription factor, and has been shown to act as a repressor. It functions in collaboration with other gap genes and their localized protein products to regulate the expression of the primary pair rule genes – even skipped (eve), hairy (h), and runt.^[15] It has been postulated that Krüppel inhibits eve expression to create the posterior boundary of eve stripe two, and evidence has also been found for Krüppel being a player specifically in the formation of hairy stripe 7.^[16][17] The expression patterns of pair rule gene will in turn regulate the segment polarity genes, making Krüppel essential for proper development along the anterior posterior axis and segment identity.

Clinical significance

Krüppel has shown homology to the mammalian Krüppel-like factors, which play key biological roles in the pathogenesis of many human diseases: cancer,^[18] obesity,^[19] inflammatory disorders^[20] and cardiovascular complications.^[21] Moreover, KLFs are known to be involved in inducible pluripotent stem cells generation, and preservation of the pluripotent state of embryonic stem cells.^[22][23][24]

See also

• Drosophila melanogaster
• Drosophila embryogenesis
• Maternal effect

References

1. Kinzler KW, Ruppert JM, Bigner SH, Vogelstein B (March 1988). "The GLI gene is a member of the Kruppel family of zinc finger proteins". Nature. 332 (6162): 371–4. Bibcode:1988Natur.332..371K. doi:10.1038/332371a0. PMID 2832761. S2CID 4279828.
2. "FlyBase Gene Report: Dmel\Kr". flybase.org. Retrieved 2019-10-08.
3. Hoy MA (January 2019). "Genetic Systems, Genome Evolution, and Genetic Control of Embryonic Development in Insects". In Hoy MA (ed.). Insect Molecular Genetics. Academic Press. pp. 103–175. doi:10.1016/B978-0-12-815230-0.00004-2. ISBN 9780128152300. {{cite book}}: |work= ignored (help)
4. Nüsslein-Volhard C, Wieschaus E (October 1980). "Mutations affecting segment number and polarity in Drosophila". Nature. 287 (5785): 795–801. Bibcode:1980Natur.287..795N. doi:10.1038/287795a0. PMID 6776413. S2CID 4337658.
5. Nüsslein-Volhard C, Wieschaus E, Kluding H (September 1984). "Mutations affecting the pattern of the larval cuticle inDrosophila melanogaster : I. Zygotic loci on the second chromosome". Wilhelm Roux's Archives of Developmental Biology. 193 (5): 267–282. doi:10.1007/BF00848156. PMID 28305337. S2CID 2195415.
6. Wieschaus E, Nusslein-Volhard C, Kluding H (July 1984). "Krüppel, a gene whose activity is required early in the zygotic genome for normal embryonic segmentation". Developmental Biology. 104 (1): 172–86. doi:10.1016/0012-1606(84)90046-0. PMID 6428949.
7. Schuh R, Aicher W, Gaul U, Côté S, Preiss A, Maier D, et al. (December 1986). "A conserved family of nuclear proteins containing structural elements of the finger protein encoded by Krüppel, a Drosophila segmentation gene". Cell. 47 (6): 1025–32. doi:10.1016/0092-8674(86)90817-2. PMID 3096579.
8. Yori JL, Seachrist DD, Johnson E, Lozada KL, Abdul-Karim FW, Chodosh LA, et al. (July 2011). "Krüppel-like factor 4 inhibits tumorigenic progression and metastasis in a mouse model of breast cancer". Neoplasia. 13 (7): 601–10. doi:10.1593/neo.11260. PMC 3132846. PMID 21750654.
9. Lin ZS, Chu HC, Yen YC, Lewis BC, Chen YW (2012). "Krüppel-like factor 4, a tumor suppressor in hepatocellular carcinoma cells reverts epithelial mesenchymal transition by suppressing slug expression". PLOS ONE. 7 (8): e43593. Bibcode:2012PLoSO...743593L. doi:10.1371/journal.pone.0043593. PMC 3427336. PMID 22937066.
10. Wei D, Gong W, Kanai M, Schlunk C, Wang L, Yao JC, et al. (April 2005). "Drastic down-regulation of Krüppel-like factor 4 expression is critical in human gastric cancer development and progression". Cancer Research. 65 (7): 2746–54. doi:10.1158/0008-5472.CAN-04-3619. PMID 15805274.
11. Lee UE, Ghiassi-Nejad Z, Paris AJ, Yea S, Narla G, Walsh M, Friedman SL (March 2010). "Tumor suppressor activity of KLF6 mediated by downregulation of the PTTG1 oncogene". FEBS Letters. 584 (5): 1006–10. doi:10.1016/j.febslet.2010.01.049. PMC 2827621. PMID 20116377.
12. Licht JD, Grossel MJ, Figge J, Hansen UM (July 1990). "Drosophila Krüppel protein is a transcriptional repressor". Nature. 346 (6279): 76–9. Bibcode:1990Natur.346...76L. doi:10.1038/346076a0. PMID 2114551. S2CID 10301966.
13. Knipple DC, Seifert E, Rosenberg UB, Preiss A, Jäckle H (1985). "Spatial and temporal patterns of Krüppel gene expression in early Drosophila embryos". Nature. 317 (6032): 40–4. Bibcode:1985Natur.317...40K. doi:10.1038/317040a0. PMID 2412131. S2CID 4340589.
14. Porcher A, Dostatni N (March 2010). "The bicoid morphogen system". Current Biology. 20 (5): R249-54. doi:10.1016/j.cub.2010.01.026. PMID 20219179.
15. Pankratz MJ, Seifert E, Gerwin N, Billi B, Nauber U, Jäckle H (April 1990). "Gradients of Krüppel and knirps gene products direct pair-rule gene stripe patterning in the posterior region of the Drosophila embryo". Cell. 61 (2): 309–17. doi:10.1016/0092-8674(90)90811-R. PMID 2331752. S2CID 44716994.
16. Small S, Kraut R, Hoey T, Warrior R, Levine M (May 1991). "Transcriptional regulation of a pair-rule stripe in Drosophila". Genes & Development. 5 (5): 827–39. doi:10.1101/gad.5.5.827. PMID 2026328.
17. La Rosée-Borggreve A, Häder T, Wainwright D, Sauer F, Jäckle H (December 1999). "hairy stripe 7 element mediates activation and repression in response to different domains and levels of Krüppel in the Drosophila embryo". Mechanisms of Development. 89 (1–2): 133–40. doi:10.1016/s0925-4773(99)00219-1. hdl:11858/00-001M-0000-002A-18E2-F. PMID 10559488. S2CID 17728959.
18. Ghaleb AM, Katz JP, Kaestner KH, Du JX, Yang VW (April 2007). "Krüppel-like factor 4 exhibits antiapoptotic activity following gamma-radiation-induced DNA damage". Oncogene. 26 (16): 2365–73. doi:10.1038/sj.onc.1210022. PMC 2230633. PMID 17016435.
19. Brey CW, Nelder MP, Hailemariam T, Gaugler R, Hashmi S (October 2009). "Krüppel-like family of transcription factors: an emerging new frontier in fat biology". International Journal of Biological Sciences. 5 (6): 622–36. doi:10.7150/ijbs.5.622. PMC 2757581. PMID 19841733.
20. Hamik A, Lin Z, Kumar A, Balcells M, Sinha S, Katz J, et al. (May 2007). "Kruppel-like factor 4 regulates endothelial inflammation". The Journal of Biological Chemistry. 282 (18): 13769–79. doi:10.1074/jbc.M700078200. PMID 17339326.
21. Rajamannan NM, Subramaniam M, Abraham TP, Vasile VC, Ackerman MJ, Monroe DG, et al. (February 2007). "TGFbeta inducible early gene-1 (TIEG1) and cardiac hypertrophy: Discovery and characterization of a novel signaling pathway". Journal of Cellular Biochemistry. 100 (2): 315–25. doi:10.1002/jcb.21049. PMC 3927779. PMID 16888812.
22. Jiang J, Chan YS, Loh YH, Cai J, Tong GQ, Lim CA, et al. (March 2008). "A core Klf circuitry regulates self-renewal of embryonic stem cells". Nature Cell Biology. 10 (3): 353–60. doi:10.1038/ncb1698. PMID 18264089. S2CID 22150633.
23. Nandan MO, Yang VW (October 2009). "The role of Krüppel-like factors in the reprogramming of somatic cells to induced pluripotent stem cells". Histology and Histopathology. 24 (10): 1343–55. doi:10.14670/HH-24.1343. PMC 2753264. PMID 19688699.
24. Takahashi K, Tanabe K, Ohnuki M, Narita M, Ichisaka T, Tomoda K, Yamanaka S (November 2007). "Induction of pluripotent stem cells from adult human fibroblasts by defined factors". Cell. 131 (5): 861–72. doi:10.1016/j.cell.2007.11.019. hdl:2433/49782. PMID 18035408. S2CID 8531539.

External links

• Diagram at Davidson College - a Drosophila embryo at the cellular blastoderm stage triple-labeled for three segmentation proteins including Krüppel (in blue) Hairy (green) and Giant (red).
• Kruppel+protein,+Drosophila at the U.S. National Library of Medicine Medical Subject Headings (MeSH)