Following the publication of the Expression of Concern on this article [1,2], concerns were raised about regions of similarity within the first two lanes in the left panel of Fig S2A of [1], and that [1] states that “thymocyte viability was not significantly reduced even without using the OP9-DL1 co-culture system (Figure S5A)” without viability percentages or statistical test results in the text or figure legend.

As noted in [2], the images provided in S1 File in [2] to support the left western blot panel of Figure S2A in [1] do not appear to match the published figure panel and did not clarify the concerns about discontinuities or similarities in the published figure. The published figure has a stronger and clearer interaction signal than the underlying images; however, the underlying images – while different from the published figure – show a band in the position that would indicate an interaction, and support the conclusion.

The corresponding author responded to state the following:

• In Figure S5A in [1], the data represent the percentage viability of thymocytes co-cultured with OP9 or OP9-DL1 cells under control, Dkk1, and Wnt 3A treatment conditions.
• The statement “thymocyte viability was not significantly reduced even without using the OP9-DL1 co-culture system” refers to a separate cell death assay performed on thymocyte cultures (presented in Figure S5B in [1]).
• The MTT assay readings (Figure S5A in [1]) were obtained using a spectrophotometer, and cell death measurements (Figure S5B in [1]) were performed using a hemocytometer under a phase contrast microscope.
• All measurements in Figure S5 in [1] were manually recorded and the data underlying Figure S5 are no longer available.
• The viability percentages are presented on the y-axes of Figures S5A and B in [1] and statistical significance for these observations was assessed using one-way ANOVA, with a p-value threshold of 0.01 considered significant for viability assays.The Figure S5 assays in [1] were conducted to confirm that no substantial differences in cell viability existed between cultures under the experimental conditions used.

The PLOS Biology Editors issue this Editorial Note to provide an update to the Expression of Concern [2] previously issued on this article [1] and to provide readers with the additional information provided about Figure S5.