Models for SPR-1 and SPR-5 function. (A)
SPR-1 and SPR-5 are part of a corepressor complex affecting the
transcription of known members of the LIN-12/Notch pathway. Although no
evidence exists, hop-1 transcription could, for example, be
affected in a cell-specific way. Alternatively, the complex could
repress the transcription of a subset of crucial genes for π cell
fate which would not get activated in lin-12(−) or
sel-12(−) mutants unless this repression is released.
(B) SPR-1/CoREST and SPR-5/p110b are part of the
LAG-1-associated corepressor complex. After ligand binding leads to the
presenilin-dependent release of the intracellular domain of LIN-12
(yellow, noted “intra”), the corepressor complex is released and a
coactivator complex formed, leading to activation of the target genes.
(C) SPR-1 and SPR-5 form a distinct corepressor complex, which
may interact with the LAG-1 repressor complex. The corepressor complex
containing SPR-1 and SPR-5 is targeted to the DNA by a factor X, and is
distinct from the LAG-1 complex. This complex, which can comprise more
factors, may cooperate with the LAG-1 complex to potentiate repression.
Association of LAG-1 and LIN-12(INTRA) might or might not release the
CoREST corepressor complex as well.