In recent years, biochemistry of blood coagulation
and fibrinolysis has advanced considerably.
However, developmental regulation of these processes
is not well understood. Studies on developmental
expression of clotting factors in humans
and other mammals have been minimal. (1,2). In
most cases, the information on regulation of many
human clotting factor genes has been obtained by
the transient expression of promoters in cell lines
(3-6). Recently, studies using the human factor IX
gene promoter in transgenic mice revealed age
dependent expression of the promoter (7). Determination
of the precise factor responsible for this
developmental effect can be more easily accomplished
if saturation mutagenized genomes are
screened for hemostasis defective mutants with
well-defined assays, which can lead to the identification
of defects in structural genes and the genes
that regulate them.