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Gene Review

hb  -  hunchback

Drosophila melanogaster

Synonyms: CG9786, Dmel\CG9786, HB, Hb, Hunchback, ...
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High impact information on hb

  • In C. elegans, a homolog of the well-known fly developmental regulator hunchback acts downstream of the microRNAs lin-4 and let-7 in a pathway controlling developmental timing [1].
  • Hunchback is necessary and sufficient for first-born cell fates, whereas Krüppel is necessary and sufficient for second-born cell fates; this is observed in multiple lineages and is independent of the cell type involved [2].
  • Based on the structure and genetic experiments, we identify putative interaction surfaces for hunchback mRNA and the cofactors Nanos and Brain Tumor. This analysis suggests that similar features in helical repeat proteins are used to bind extended peptides and RNA [3].
  • Binding of pumilio to maternal hunchback mRNA is required for posterior patterning in Drosophila embryos [4].
  • Sites in hb mRNA that mediate this repression, named nanos response elements (NREs), have been identified [4].

Biological context of hb

  • Here we show that the Bcd gradient displays a high embryo-to-embryo variability, but that this noise in the positional information is strongly decreased ('filtered') at the level of hunchback (hb) gene expression [5].
  • Activation appears to depend on cooperative interactions among bcd and hb proteins, since disrupting single binding sites cause catastrophic reductions in expression. gt is directly involved in the formation of the anterior border, although additional repressors may participate in this process [6].
  • A 142 bp core fragment containing one low affinity hb and five medium to strong bcd protein binding sites drives gene expression in a Kr-like location in the centre of the embryo [7].
  • We further demonstrate that while the amino-terminal domain is largely dispensable for cooperative binding to the hb enhancer element, it is preferentially required for cooperative binding to the kni enhancer element [8].
  • These results suggest that the individual phases of hb transcription, which overlap temporally and spatially, contribute specific patterning functions in early embryogenesis [9].

Anatomical context of hb

  • The function of the latter class appears to be linked to the secondary expression of hb in the parasegment 4 (PS4) stripe at blastoderm stage [10].
  • In Clogmia hb expression deviates from that known in Drosophila in two main respects: (1) it shows an extended dorsal domain that is linked to the large serosa anlage, and (2) it shows a terminal expression in the proctodeal region [11].
  • Hunchback is required for the specification of the early sublineage of neuroblast 7-3 in the Drosophila central nervous system [12].
  • In Drosophila, the first temporal identity of most neural stem cells (neuroblasts) in the embryonic ventral nerve cord is specified by the transient expression of the transcription factor Hunchback [13].
  • Using hb-promoter/lacZ fusion gene constructs in combination with germ line transformation, we have delimited a regulatory region for the 2.9-kb transcript to approximately 300 bp upstream of the site of transcription initiation and show that this region is sufficient to confer the full regulation by bcd [14].

Physical interactions of hb

  • The products of the Drosophila gap genes hunchback and Krüppel bind to the hunchback promoters [15].
  • We have recently shown that Bcd binds cooperatively to a hb enhancer element and proposed that cooperative DNA binding is facilitated by an interaction between Bcd molecules [16].
  • Embryonic silencing is initiated by hb protein which binds to the silencers to repress Ubx, thereby defining the Ubx domain [17].
  • These results imply that the Polycomb complex is not dependent on hunchback and suggest that the pattern of silencing reflects rather the state of activity of the gene at the time the Polycomb complex is formed [18].
  • The PUMILIO (PUM) protein is thought to bind the NREs and thereby repress hb translation [19].

Regulatory relationships of hb

  • hunchback has an anterior and posterior expression pattern in Drosophila [20] [21], [22]. In the anterior half of the embryo, hunchback shows a sharp on-off expression pattern and depends on Bcd [20], [21] and on its own self-regulation [21], [22]. It has been recently shown that hunchback sharpness is due to spatial bistability stemming from hb self-regulation [23]. The position of the hb pattern is controlled by Bicoid cooperative binding, but this mechanism itself is not sufficient to generate hb’s expression sharpness [23].
  • Zygotic expression of hb is directly activated by the bcd gene product, leading to a subdivision of the embryo into an anterior half expressing zygotically provided hb protein and a posterior half that does not [24].
  • We conclude that hb represses Ubx expression directly by binding to BRE and probably other Ubx regulatory elements [25].
  • We show here that the abdominal cad domain is regulated by the hunchback (hb) gradient through repression at high concentrations and activation at low concentrations of HB protein [26].
  • We demonstrate that posterior stripe boundaries are established by gap protein repressors unique to each stripe: h stripe 5 is repressed by the giant (gt) protein on its posterior border and h stripe 6 is repressed by the hunchback (hb) protein on its posterior border [27].
  • Furthermore, the maintenance of hb expression in the GMC is regulated by the activity of Prospero (Pros), a transcription factor which asymmetrically segregates into the GMC during mitosis and inhibits Svp activity on both, the transcriptional and posttranscriptional level [28].

Other interactions of hb

  • In contrast to the Bcd gradient, the hb expression pattern already includes the information about the scale of the embryo [5].
  • A morphogenetic gradient of hunchback protein organizes the expression of the gap genes Krüppel and knirps in the early Drosophila embryo [24].
  • By ensuring correct POU gene expression boundaries, hb and cas maintain temporal subdivisions in the cell-identity circuitry controlling CNS development [29].
  • The repressor of the anterior Ubx expression is the gap gene hunchback (hb) [25].
  • Zygotic caudal regulation by hunchback and its role in abdominal segment formation of the Drosophila embryo [26].

Analytical, diagnostic and therapeutic context of hb


  1. MicroRNA pathways in flies and worms: growth, death, fat, stress, and timing. Ambros, V. Cell (2003) [Pubmed]
  2. Drosophila neuroblasts sequentially express transcription factors which specify the temporal identity of their neuronal progeny. Isshiki, T., Pearson, B., Holbrook, S., Doe, C.Q. Cell (2001) [Pubmed]
  3. Structure of Pumilio reveals similarity between RNA and peptide binding motifs. Edwards, T.A., Pyle, S.E., Wharton, R.P., Aggarwal, A.K. Cell (2001) [Pubmed]
  4. Binding of pumilio to maternal hunchback mRNA is required for posterior patterning in Drosophila embryos. Murata, Y., Wharton, R.P. Cell (1995) [Pubmed]
  5. Establishment of developmental precision and proportions in the early Drosophila embryo. Houchmandzadeh, B., Wieschaus, E., Leibler, S. Nature (2002) [Pubmed]
  6. Regulation of even-skipped stripe 2 in the Drosophila embryo. Small, S., Blair, A., Levine, M. EMBO J. (1992) [Pubmed]
  7. Gene expression mediated by cis-acting sequences of the Krüppel gene in response to the Drosophila morphogens bicoid and hunchback. Hoch, M., Seifert, E., Jäckle, H. EMBO J. (1991) [Pubmed]
  8. Enhancer sequences influence the role of the amino-terminal domain of bicoid in transcription. Fu, D., Zhao, C., Ma, J. Mol. Cell. Biol. (2003) [Pubmed]
  9. Thoracic patterning by the Drosophila gap gene hunchback. Wu, X., Vasisht, V., Kosman, D., Reinitz, J., Small, S. Dev. Biol. (2001) [Pubmed]
  10. Differential regulation of target genes by different alleles of the segmentation gene hunchback in Drosophila. Hülskamp, M., Lukowitz, W., Beermann, A., Glaser, G., Tautz, D. Genetics (1994) [Pubmed]
  11. Segmentation gene expression in the mothmidge Clogmia albipunctata (Diptera, psychodidae) and other primitive dipterans. Rohr, K.B., Tautz, D., Sander, K. Dev. Genes Evol. (1999) [Pubmed]
  12. Hunchback is required for the specification of the early sublineage of neuroblast 7-3 in the Drosophila central nervous system. Novotny, T., Eiselt, R., Urban, J. Development (2002) [Pubmed]
  13. Timing of identity: spatiotemporal regulation of hunchback in neuroblast lineages of Drosophila by Seven-up and Prospero. Mettler, U., Vogler, G., Urban, J. Development (2006) [Pubmed]
  14. Differential regulation of the two transcripts from the Drosophila gap segmentation gene hunchback. Schröder, C., Tautz, D., Seifert, E., Jäckle, H. EMBO J. (1988) [Pubmed]
  15. The products of the Drosophila gap genes hunchback and Krüppel bind to the hunchback promoters. Treisman, J., Desplan, C. Nature (1989) [Pubmed]
  16. Sequences outside the homeodomain of bicoid are required for protein-protein interaction. Yuan, D., Ma, X., Ma, J. J. Biol. Chem. (1996) [Pubmed]
  17. Imaginal disc silencers from Ultrabithorax: evidence for Polycomb response elements. Christen, B., Bienz, M. Mech. Dev. (1994) [Pubmed]
  18. Hunchback-independent silencing of late Ubx enhancers by a Polycomb Group Response Element. Poux, S., Kostic, C., Pirrotta, V. EMBO J. (1996) [Pubmed]
  19. The PUMILIO-RNA interaction: a single RNA-binding domain monomer recognizes a bipartite target sequence. Zamore, P.D., Bartel, D.P., Lehmann, R., Williamson, J.R. Biochemistry (1999) [Pubmed]
  20. The gradient morphogen bicoid is a concentration-dependent transcriptional activator. Struhl, G., Struhl, K., Macdonald, P.M. Cell. (1989) [Pubmed]
  21. The bicoid protein is a positive regulator of hunchback transcription in the early Drosophila embryo. Driever, W., Nüsslein-Volhard, C. Nature. (1989) [Pubmed]
  22. The products of the Drosophila gap genes hunchback and Krüppel bind to the hunchback promoters. Treisman, J., Desplan, C. Nature. (1989) [Pubmed]
  23. Spatial bistability generates hunchback expression sharpness in the Drosophila embryo. Lopes, F.J., Vieira, F.M., Holloway, D.M., Bisch, P.M., Spirov, A.V. PLoS. Comput. Biol. (2008) [Pubmed]
  24. A morphogenetic gradient of hunchback protein organizes the expression of the gap genes Krüppel and knirps in the early Drosophila embryo. Hülskamp, M., Pfeifle, C., Tautz, D. Nature (1990) [Pubmed]
  25. The bx region enhancer, a distant cis-control element of the Drosophila Ubx gene and its regulation by hunchback and other segmentation genes. Qian, S., Capovilla, M., Pirrotta, V. EMBO J. (1991) [Pubmed]
  26. Zygotic caudal regulation by hunchback and its role in abdominal segment formation of the Drosophila embryo. Schulz, C., Tautz, D. Development (1995) [Pubmed]
  27. Positioning adjacent pair-rule stripes in the posterior Drosophila embryo. Langeland, J.A., Attai, S.F., Vorwerk, K., Carroll, S.B. Development (1994) [Pubmed]
  28. Connecting temporal identity to mitosis: the regulation of Hunchback in Drosophila neuroblast lineages. Urban, J., Mettler, U. Cell Cycle (2006) [Pubmed]
  29. Regulation of POU genes by castor and hunchback establishes layered compartments in the Drosophila CNS. Kambadur, R., Koizumi, K., Stivers, C., Nagle, J., Poole, S.J., Odenwald, W.F. Genes Dev. (1998) [Pubmed]
  30. A development genetic analysis of the gene regulator of postbithorax in Drosophila melanogaster. Bender, M., Turner, F.R., Kaufman, T.C. Dev. Biol. (1987) [Pubmed]
  31. A small region surrounding the distal promoter of the hunchback gene directs maternal expression. Margolis, J.S., Borowsky, M., Shim, C.W., Posakony, J.W. Dev. Biol. (1994) [Pubmed]
  32. hunchback, a gene required for segmentation of an anterior and posterior region of the Drosophila embryo. Lehmann, R., Nüsslein-Volhard, C. Dev. Biol. (1987) [Pubmed]
  33. High sequence turnover in the regulatory regions of the developmental gene hunchback in insects. Hancock, J.M., Shaw, P.J., Bonneton, F., Dover, G.A. Mol. Biol. Evol. (1999) [Pubmed]
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