part of prestalk region of the tipped mound prestalk O region prestalk O region of the tipped mound Area of the prestalk zone of the tipped mound located posterior to the pstA region and characterized by low expression of the ecmA gene directed by the distal part of its promoter (ecmO promoter). DDANAT:0000102 Dictyostelium_discoideum_anatomy pstO region of the tipped mound