DDX4 and Infertility: In contrast, a more recent study by Feng et al.27, using Stra8-GFP-Cre and tamoxifen-induced Ddx4-CreERT2 deletion models also targeting exon 6 of Kdm2a, reported reduced testis weight, infertility, and defects in meiotic initiation and progression that was associated with reduced activation of meiotic gene expression in juvenile mice.