Biology Reference
In-Depth Information
from the human
APOA1
gene promoter (Bochkanov
et al
., 1990; Higuchi
et al
.,
1988; Pan
et al
., 1987). These sequences may help to explain the differing tissue
specificity of this gene between the two species.
The rat tissue-type plasminogen activator gene differs from that of mouse and
human (
PLAT
; 8p12) in that it is induced by gonadotropins via a cAMP-depen-
dent pathway. The rat
Plat
gene promoter possesses a cAMP-responsive element
(CRE) but, at the corresponding location in the murine and human gene promot-
ers, a single base-pair change is present that serves to reduce drastically the bind-
ing affinity to CRE-binding protein (Holmberg
et al
., 1995). This difference is
sufficient to account for the unresponsiveness of the human and murine gene pro-
moters to forskolin and follicle-stimulating hormone.
The promoters of the murine and human lactoferrin (
LTF
; 3p21.2-p21.3) genes
have numerous
cis
-acting regulatory motifs in common. However, in the bovine
lactoferrin gene, several of these motifs (GATA-1, Oct-1, COUP, AP-2, and gluco-
corticoid and acute phase response elements) are absent, providing a possible
explanation of the relatively weak expression of bovine lactoferrin in comparison
to human and mouse (Seyfert
et al
., 1994).
Both tumor necrosis factor
and lipopolysaccharide stimulate the expression
of P-selectin in murine endothelial cells but this does not occur in human
endothelial cells. This difference is thought to be explicable in terms of structural
differences in the promoters of the P-selectin genes between the two species (Pan
et al
., 1998). The promoter of the human P-selectin (
SELP
; 1q23-q25) gene pos-
sesses a unique NF
B binding site which is thought to be specific for p50 or p52
homodimers. Its murine counterpart contains two tandem NF
B binding sites
and a variant activating transcription factor/cAMP response element which is
similar to that found in the E-selectin gene required for tumor necrosis factor
-
and lipopolysaccharide-inducible expression.
The promoters of the human and murine
XRCC5
DNA repair genes (2q35) dif-
fer with respect to the number of copies of a 21 bp near-perfect palindromic ele-
ment (Kpb); the mouse
Xrcc5
gene possesses a single copy whereas the human
XRCC5
gene possesses seven copies (Ludwig
et al
., 1997). Amplification of this
cis
-acting element occurred in the human lineage and this may help to account for
the human
XRCC5
promoter being at least three to five-fold stronger than its
murine counterpart (Ludwig
et al
., 1997).
Calbindin-D
9k
is a mammalian-specific cytosolic calcium-binding protein
which is encoded by a gene (
CALB3
; Xp) that is ubiquitously expressed in the
intestine. In the rat, this gene is also expressed in the uterus under the control of
estrogen whose effects are mediated by an estrogen response element (ERE)
(Darwish
et al
., 1990). By contrast, uterine expression is not found in human or
baboon. In these primates, two nucleotide substitutions are present that have
abolished the binding affinity of the ERE to the estrogen receptor and probably
account for the loss of uterine expression (Jeung
et al
., 1994; 1995).
The chorionic gonadotropin
-chain gene is expressed in the pituitary of all
mammals but is expressed in the placenta only in primates and horses. Since
horses and primates are only distantly related, and species such as the cow and
rodents which are more closely related to horses than primates do not express the
gene in placenta, it would appear as if the placental expression of the gene has been