Polycomb-group proteins

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Polycomb-group proteins (PcG proteins) are a

embryonic development in fruit flies (Drosophila melanogaster). They derive their name from the fact that the first sign of a decrease in PcG function is often a homeotic transformation of posterior legs towards anterior legs, which have a characteristic comb-like set of bristles.[1]

In insects

In

Cellular Memory Modules (CMMs). Trithorax-group (trxG) proteins maintain the active state of gene expression while the Polycomb-group (PcG) proteins counteract this activation with a repressive function that is stable over many cell generations and can only be overcome by germline differentiation processes. Polycomb Gene complexes or PcG silencing consist of at least three kinds of multiprotein complex Polycomb Repressive Complex 1 (PRC1), PRC2 and PhoRC
. These complexes work together to carry out their repressive effect. PcGs proteins are evolutionarily conserved and exist in at least two separate protein complexes; the PcG repressive complex 1 (PRC1) and the PcG repressive complex 2–4 (PRC2/3/4). PRC2 catalyzes trimethylation of lysine 27 on histone H3 (H3K27me2/3), while PRC1 mono- ubiquitinates histone H2A on lysine 119 (H2AK119Ub1).

In mammals

In mammals Polycomb Group gene expression is important in many aspects of development like

ink4 locus (p16Ink4a, p19Arf).[4][7]

Regulation of Polycomb-group proteins at bivalent chromatin sites is performed by SWI/SNF complexes, which oppose the accumulation of Polycomb complexes through ATP-dependent eviction.[8]

In plants

In Physcomitrella patens the PcG protein FIE is specifically expressed in stem cells such as the unfertilized egg cell. Soon after fertilisation the FIE gene is inactivated in the young embryo.[9] The Polycomb gene FIE is expressed in unfertilised egg cells of the moss Physcomitrella patens and expression ceases after fertilisation in the developing diploid sporophyte.

It has been shown that unlike in mammals the PcG are necessary to keep the cells in a differentiated state. Consequently, loss of PcG causes de-differentiation and promotes embryonic development.[10]

Polycomb-group proteins also intervene in the control of flowering by silencing the Flowering Locus C gene.[11] This gene is a central part of the pathway that inhibits flowering in plants and its silencing during winter is suspected to be one of the main factors intervening in plant vernalization.[12]

The Polycomb gene FIE is expressed (blue) in unfertilised egg cells of the moss Physcomitrella patens (right) and expression ceases after fertilisation in the developing diploid sporophyte (left). In situ GUS staining of two female sex organs (archegonia) of a transgenic plant expressing a translational fusion of FIE-uidA under control of the native FIE promoter

See also

References

  1. ISBN 978-1-904455-25-7
    .
  2. PMID 18974828
    .
  3. ^ Heurtier, V., Owens, N., Gonzalez, I. et al. The molecular logic of Nanog-induced self-renewal in mouse embryonic stem cells. Nat Commun 10, 1109 (2019). https://doi.org/10.1038/s41467-019-09041-z
  4. ^
    PMID 15964994
    .
  5. PMID 14722607
    .
  6. PMID 18447587
    .
  7. PMID 20716961
    .
  8. PMID 27941795
    .
  9. PMID 19542356
    .
  10. PMID 19680533
    .
  11. PMID 18852898
    .
  12. PMID 10716723
    .

Further reading

External links
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