SETD1A and cyst: At day 3 post-eclosion, although 45% of Set1 KD testes had germline loss, 55% had an early germ cell overpopulation phenotype, whereby the germ cells surrounding the hub formed a large, disorganized cluster with very few intercalating cyst cells and were often devoid of or had very few late-stage spermatocytes (Fig. 1C,D).