Gap gene

<h2 id="gene-activation">Gene activation</h2>
<p>Expression of tailless is activated by torso protein in the poles of the embryo. Tailless is also regulated in a complex manner by the maternal-effect gene bicoid.
</p><p>Both embryonically transcribed hunchback and maternally transcribed hunchback are activated by bicoid protein in the anterior and is inhibited in the posterior by nanos protein. Embryonically transcribed hunchback protein is able to exhibit the same effects on <a href="/facts/Kr%25C3%25BCppel/8KP33WSJ">Krüppel</a> and knirps as maternally transcribed hunchback.
</p><p>The Krüppel gene is activated when the bicoid protein gradient declines steeply, at the central part of the embryo. Krüppel is regulated by five regulatory proteins: bicoid, hunchback, tailless, knirps and giant. Krüppel is inhibited by high levels of hunchback, high levels of giant, and tailless, which establishes the anterior boundary of Krüppel expression. Krüppel is also inhibited by knirps and activated by low levels of bicoid and low levels of hunchback, which establishes the posterior boundary of Krüppel expression.
</p><p>The knirps gene appears to be spontaneously activated. It is repressed by hunchback. Hunchback repression thus defines the anterior boundary of the knirps gene. Due to more efficient inhibition of the knirps gene by hunchback, knirps is expressed more posteriorly in the embryo compared to Krüppel. Tailless protein inhibits knirps gene expression in the posterior part of the embryo, allowing the knirps protein to be expressed only in the central part of the embryo (but more posterior compared to Krüppel). This is due to the ability of both hunchback and tailless to bind to the enhancer regions of knirps.
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<h2 id="mechanism-of-action">Mechanism of action</h2>
<p>The gap genes code for transcription factors that regulate the expression of <a href="/facts/Pair-rule_gene/puIQ44PI">pair-rule genes</a> and homeotic genes <a class="footnote-ref" id="fnref:8" href="#fn:8"><sup>8</sup></a>  by competing for binding to their enhancer regions.
It has been demonstrated that gap gene expression in the <i>Drosophila</i> blastoderm exhibit a property called canalization, a property of developing organisms to produce a consistent phenotype despite variations in genotype or environment. It has been proposed that canalization is a manifestation of cross regulation of gap genes expression and can be understood as arising from the actions of attractors in the gap gene dynamical system.<a class="footnote-ref" id="fnref:9" href="#fn:9"><sup>9</sup></a>
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<h2 id="see-also">See also</h2>
<ul><li><a href="/facts/Drosophila_embryogenesis/CRro4E9n"><i>Drosophila</i> embryogenesis</a></li>
<li><a href="/facts/Pair-rule_gene/puIQ44PI">Pair-rule gene</a></li></ul>

<h2 id="external-links">External links</h2>
<ul><li>The Interactive Fly: <a href="http://www.sdbonline.org/fly/aignfam/gapnprl.htm">http://www.sdbonline.org/fly/aignfam/gapnprl.htm</a></li></ul>

<h2 id="references">References</h2>

<ol>
<li id="fn:1"><p>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. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:1" class="footnote-back-ref">↩</a></p></li>
<li id="fn:2"><p>Petschek JP, Perrimon N, Mahowald AP (January 1987). "Region-specific defects in l(1)giant embryos of Drosophila melanogaster". Developmental Biology. 119 (1): 175–89. doi:10.1016/0012-1606(87)90219-3. PMID 3098602. <a href="/wiki/Perrimon_N" target="_blank">/wiki/Perrimon_N</a> <a href="#fnref:2" class="footnote-back-ref">↩</a></p></li>
<li id="fn:3"><p>Weigel D, Jürgens G, Klingler M, Jäckle H (April 1990). "Two gap genes mediate maternal terminal pattern information in Drosophila". Science. 248 (4954): 495–8. Bibcode:1990Sci...248..495W. doi:10.1126/science.2158673. PMID 2158673. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:3" class="footnote-back-ref">↩</a></p></li>
<li id="fn:4"><p>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. <a href="/wiki/Bibcode_(identifier)" target="_blank">/wiki/Bibcode_(identifier)</a> <a href="#fnref:4" class="footnote-back-ref">↩</a></p></li>
<li id="fn:5"><p>Bender M, Horikami S, Cribbs D, Kaufman TC (1988). "Identification and expression of the gap segmentation gene hunchback in Drosophila melanogaster". Developmental Genetics. 9 (6): 715–32. doi:10.1002/dvg.1020090604. PMID 2849517. <a href="/wiki/Doi_(identifier)" target="_blank">/wiki/Doi_(identifier)</a> <a href="#fnref:5" class="footnote-back-ref">↩</a></p></li>
<li id="fn:6"><p>Gilbert, SF (2000). "The Origins of Anterior-Posterior Polarity". Developmental Biology (6th ed.). Sunderland (MA): Sinauer Associates. Retrieved 23 October 2015. <a href="https://www.ncbi.nlm.nih.gov/books/NBK10039/" target="_blank">https://www.ncbi.nlm.nih.gov/books/NBK10039/</a> <a href="#fnref:6" class="footnote-back-ref">↩</a></p></li>
<li id="fn:7"><p>Schetne, Lauren. "Segmentation Genes in Drosophila Development: Pair Rule, Segment Polarity & Gap Genes". Study.com. Retrieved 23 October 2015. <a href="https://study.com/academy/lesson/segmentation-genes-in-drosophila-development-pair-rule-segment-polarity-gap-genes.html" target="_blank">https://study.com/academy/lesson/segmentation-genes-in-drosophila-development-pair-rule-segment-polarity-gap-genes.html</a> <a href="#fnref:7" class="footnote-back-ref">↩</a></p></li>
<li id="fn:8"><p>Ingham, P. W.; D. Ish-Horowicz & K. R. Howard (1986). "Correlative changes in homoeotic and segmentation gene expression in Krüppel mutant embryos of Drosophila". The EMBO Journal. 5 (7): 1659–1665. doi:10.1002/j.1460-2075.1986.tb04409.x. PMC 1166992. PMID 16453692. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1166992" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1166992</a> <a href="#fnref:8" class="footnote-back-ref">↩</a></p></li>
<li id="fn:9"><p>V.V, Gursky; L. Panok; E.M. Myasnikova; Manu, M.G. Samsonova; J. Reinitz & A.M. Samsonov (July 2011). "Mechanisms of gap gene expression canalization in the Drosophila blastoderm". BMC Systems Biology. 5 (118): 118. doi:10.1186/1752-0509-5-118. PMC 3398401. PMID 21794172. <a href="https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3398401" target="_blank">https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3398401</a> <a href="#fnref:9" class="footnote-back-ref">↩</a></p></li>
</ol>

Gap gene open-in-new

Gap gene