Plays an essential role in the Tl receptor signaling pathway that establishes embryonic dorsoventral polarity; the signal directs import of dl into ventral and ventrolateral nuclei, thereby establishing dorsoventral polarity. Tub recruits pll to the plasma membrane and protein-protein interaction activates pll. Also has a role in pupal pattern formation. Interacts (via Death domain) with pll (via Death domain). Associates with the plasma membrane during interphase syncytial blastoderm embryos, more specifically at the membrane invaginations around the nuclei. Later in embryonic development protein is entirely cytoplasmic. Expressed both maternally and zygotically. Zygotic expression is highest in late larval development. Phosphorylated by pll.