Genetic regulatory networks controlling early PLM and ALM development. Direct relationships, illustrated by continuous lines, are defined by 3 criteria: (1) target gene expression is affected by perturbation of activator; (2) target gene and activator are coexpressed; (3) target gene promoter/enhancer sequences contain binding sites for activators, or length of time between perturbation of activator and effect on target gene is probably insufficient to allow for synthesis of intermediates. Where criteria 1 and 2 are met but 3 is unknown, the relationship is described as indirect and depicted by a dashed line. PLM (erythroid): the data show that initiation of gata1 and c-myb expression is both Scl and Lmo2 dependent. Initially, runx1 expression is dependent on Scl and Lmo2, while hhex and draculin are Scl and Lmo2 independent. After 7s, hhex and draculin become dependent on Scl and Lmo2, and runx1 expression gradually becomes Scl and Lmo2 independent. ALM (myeloid): pu.1 expression is initially dependent on Scl and Lmo2, while hhex and draculin are independent. After 7s, hhex and draculin become Scl and Lmo2 dependent. Unknown activators of Scl- and Lmo2-independent genes are depicted as genes X, Y, and Z. It is possible that X and Y represent the same gene due to similarities in timing of involvement.