Fig. 7

Model for germ line determination in O. dioica. This model is based on our in situ data for pum1 and vas 4. The model emphasizes how germ line determination may take place during gastrulation. a) Schematic representation of an embryo at the early gastrulation stage. The position of the small B6.4 cells containing maternal pum1 transcripts are indicated. b) A close up of B6.4 cells that have embarked on mitosis during gastrulation. This stage corresponds to the transition from a 32-cell to a 64-cell stage embryo. Each of the cells now contain a pair of nuclei and maternal pum1 transcripts. c) Schematic representation of the outcome of the division of the B6.4 cells. Two PGCs lacking maternal transcripts and two somatic cells containing maternal pum1 transcripts are depicted. At this stage of development germ-soma segregation is completed. d) The two PGCs depicted initiate expression of the germ cell marker vas4 when they have ingressed during gastrulation. The two somatic cells depicted have lost the maternal pum1 transcripts and they do not ingress during gastrulation. The circumference of the two somatic cells is shown with dashed lines indicating that these cells may undergo apoptosis