(A, C, and E) U-2 OS cells were transfected with doses of siRNA as indicated, and gene expression was measured from samples collected 48 h after transfection. Knockdown of Cry1 (A), Rev-erb beta (C), and Per1 (E) leads to increased expression of the gene paralogs Cry2, Rev-erb alpha, and Per2 and Per3, respectively.
(B, D, F, and G) The response is unidirectional, as a decrease of Cry2 (B), Rev-erb alpha (D), Per2 (F), or Per3 (G) does not result in an increase of respective gene paralogs.
(H) Transcriptional repressors could directly regulate the expression of their gene paralog through response elements (RE) in upstream regulatory regions (H) (modified from [25]). In the case of the circadian clock network, we propose direct regulation of Cry1, Per1, and Rev-erb beta (Repressor 1) by Cry2, Per2/3, or Rev-erb alpha (Repressor 2), respectively.