In several developmental biology contexts, the fate of maternal somatic cells commits prior to and directs the developmental potential of the embryo itself. This pre-embryonic determination is crucial in setting up the earliest body axes and cell lineages. Among key models, certain species exemplify this mechanism during specific events:

1. Specification of Primary Organizer in Amphibians: This involves embryonic cell interactions post-fertilization, without primary maternal somatic cell fate determination.

2. Specification of Dorsoventral Axis in Drosophila: Maternal somatic follicle cells surrounding the oocyte determine the dorsoventral polarity by producing signals like Gurken. This maternal input is established before fertilization and thus sets the foundation for embryonic axis formation. Hence, maternal somatic cell fate is determined first, influencing embryo fate.

3. Formation of Vulval Precursor Cells in C. elegans: Cell fate here emerges from embryonic and larval cell signaling, largely independent of maternal somatic cell fate.

4. Specification of Micromeres in Sea Urchin: Micromere specification involves autonomous embryonic cell division patterns, not maternal somatic cell fate.

Considering these developmental processes, the event where maternal somatic cell fate is determined first and then directs embryo fate is the specification of the dorsoventral axis in Drosophila.

Answer: (2) The specification of dorso-ventral axis in Drosophila