tgrB1 and tgrC1 are involved in kin discrimination. They play an essential role in aggregation and subsequent development. Could function as a non-diffusible cell-cell signaling molecule that is required for multicellular development. Has both cell-autonomous and non-cell-autonomous functions. Terminal node, epistatic both to comC and tgrD1. Activates tgrD1. Expressed at low levels in the mid-aggregation stage, followed by a rapid increase that coincides with the completion of aggregate formation. Expression is greatest in cells at the periphery and the rear end of the migrating slug. Induced at the loose aggregate stage and expressed through the remainder of development. Mutant cells are unable to sporulate in isolation although they will sporulate when in the presence of wild-type cells. Cells form loose aggregates before disaggregating. After starvation, cells form wide streams that frequently break and form secondary centers before reaching the primary center and display cAMP relay defects. Cells fail to rotate. tgrB1 and tgrC1 double mutants show strain segregation in chimeras with wild-type cells. ComC, tgrC1 and tgrD1 triple mutants fail to form spores. The tgrC1 gene is highly polymorphic.