In the 24 months aging trajectory, expression of genes associated with quiescence, such as Bmp2 and Cdkn1a, was elevated toward the end point of 24 months (Figure 2F), consistent with the notion that aged HF-SCs mostly rest in the prolonged quiescent state (Keyes et al., 2013; Ge et al., 2020; Zhang et al., 2021). Here, CDKN1A is linked to hydrops fetalis.