Clinical Biochemistry of Domestic Animals (Sixth Edition) - UMK ...

II. Anterior Lobe and Intermediate Lobe
583
Pig LPICPSGAVNCQMSLRDLFDRAVILSHYIHNLSSEMFNEFDKRYAQGRGFITKAINSCHTSSLSTPEDKE 70
Horse ------------V---E---------------------------------V-------------------
Dog ------------V---------------------------------------------------------
Cat ------------V--------------------------------------------------P------
Goat T-V--N-PG---V----------MV----------------------K-Y--MAL--------P------
Sheep T-V--N-PGD--V----------MV----------------------K----MAL--------P------
Cattle T-V--N-PG---V----------MV-----D----------------K----MAL--------P------
Human -----G--AR--VT---------V-------------S------TH-------AI--------A------
Rat --V-SG- D--TP-PE----V-M------T-YTD--I----Q-V-D-E--A-A--D-P----A------
Mouse ----SA- D--T---E----V--------T-YTD--I----Q-V-D-E-MV-V--D-P----A------
* * * ** * **** * ***** * ** **** * * * **** ******
Pig QAQQIHHEVLLNLILRVLRSWNDPLYHLVTEVRGMQEAPDAILSRAIEIEEQNKRLLEGMEKIVGQVHPG 140
Horse --------D--------------------S---------E----K--------R-------------Q-R
Dog --------D--------------------------------------------R----------------
Cat --------D---V---------------------LH-----------------R----------H-----
Goat ----T-----MS---GL------------------KGV-------------E---------M-F---I--
Sheep ----T-----MS---GL------------------KGV-------------E---------M-F---I--
Cattle ----T-----MS---GL------------------KG--------------E---------M-F---I--
Human ----MNQKDF-S--VSI-----E----------------E----K-V-----T--------L--S----E
Rat ---KVPP--------SLVH------FQ-I-GLG-IH------I---K------------I---IS-AY-E
Mouse --LKVPP--------SLVQ-SSDPLFQ-I-GVG-I----EY-----K-------Q----V---IS-AY-E
** * * * * * * * * * **** **** * * * *
Pig IKENEVYSVWSGLPSLQMADEDTRLFAFYNLLHCLRRDSHKIDNYLKLLKCRIIYDSNC 199
Horse ----------------------S------------------------------V-----
Dog -R---------------------------------------------------V-----
Cat VR--------------------S--------------------S---------V-----
Goat A-ET-P-P---------TK--EA-HS-------------S---T-----N-----NN--
Sheep A-ET-P-P---------TK---A-HS-------------S---T-----N-----NN--
Cattle A--T-P-P---------TK---A-YS-------------S---T-----N-----NN--
Human T-EN-I-P-------------ES--S-Y--------------------------HNN--
Rat A-GN-I-L---Q-----GV--ESKDL----NIR--------V-----F-R-Q-VHKN--
Mouse A-GNGI-F---Q-----GV--ESKILSLRNTIR----H---V--F--V-R-Q-AHQN--
* *** ***** ** **** * * * ** * * * **
FIGURE 18-13 Sequence comparison of PRL. See the legend for Figure 18-6 .
Cat
Dog
Horse
Pig
Goat
Sheep
Cattle
Human
Mouse
Rat
It should be kept in mind that the reference values for
plasma IGF-I concentrations in the dog are breed ( body
size) dependent.
2 . Prolactin
a . Gene Expression
Prolactin (PRL) is encoded by a single gene in humans. In
nonprimates, a family of PRL-related genes is found and only
one gene encoding GH. In the rat, a PRL family of at least
24 related genes can be found including the placental lactogens,
proliferans, and PRL-like proteins (PLPs) ( Alam et al. ,
2006 ). In the cow, an expanded PRL family also has been
found; however, its members are not orthologous with members
of the mouse and rat PRL family genes ( Soares, 2004 ).
Expansion of the PRL family does not exist in the dog.
The appearance of specific PRL-producing lactotropes
is one of the latest events in pituitary development. It has
been proposed that lactotropes arise from somatotropes or
at least a common progenitor cell, the somatomammotrope
( Burrows et al. , 1999 ). In chicken, however, evidence is
presented that lactotropes do not differentiate from somatotropes
during embryonic development ( Fu et al. , 2004 ). In
mouse pituitaries, mammosomatotropes represent only 5%
to 6% of somatotropes ( Villalobos et al. , 2004 ).
The Pit-1 transcription factor is a prerequisite factor
for PRL expression, as it is for GH and TSH. In the PRL
gene Pit-1 acts in synergy with an estrogen nuclear receptor
(ER) at a distal enhancer site, with two ETS-domaincontaining
factors (Ets-1 and ERF) and the Pitx1 and Pitx2
transcription factors ( Dasen and Rosenfeld, 2001 ). The
expression and release of PRL are under tonic dopaminergic
inhibitory control. No consensus exists on the identity of
physiologically relevant PRL releasing factors. In extracts
of the bovine posterior pituitary, a PRL-releasing factor was
found ( Hashizume et al. , 2005 ). The melanocortin peptide
γ 3-MSH also stimulates PRL expression ( Langouche et al. ,
2004 ), whereas a variety of factors are found that stimulate
PRL release, such as PRL-releasing peptide (PrRP), TRH,
oxytocin, VIP, angiotensin II, PACAP, and intermedin and
may also stimulate PRL gene expression.
The PRL gene, like the GH gene, has five exon areas.
In the pituitary, a promoter upstream of the Cap site in
exon 1b is used, outside the pituitary expression of PRL is
regulated by a second promoter upstream of exon 1a initially
described for PRL expression in decidua and lymphocytes
( Gerlo et al. , 2006 ; Goffin et al. , 2002 ).
b . (Pro)hormone
Prolactin (PRL) is synthesized as a single polypeptide,
which, after cleavage of the signal peptide, has a molecular
weight of approximately 23,000 daltons and three intrachain
disulfide bridges. There is a good deal of variability in the
sequences of PRL from different species. The rat and mouse
PRL are most distinct and differ from the other sequences
at about 40% of all amino acid residues ( Fig. 18-13 ).