PROX1 and hydrops fetalis: Interestingly, some of the regulatory genes involved in the development of the HF, such as those encoding some molecules of the Wnt/β catenin pathway, some TCFs (mostly TCF4), and Prox1, continue to be expressed and are functional in the adult dentate gyrus (Shimogori et al., 2004; Karalay et al., 2011), and at least Wnt signaling and Prox1 play important roles in distinct aspects of adult neurogenesis, such as cell proliferation or the differentiation of new granule cells (Karalay et al., 2011; Iwano et al., 2012; Varela-Nallar and Inestrosa, 2013).