(Received for publication, April 28, 1995; and in revised form, August 21, 1995)
From the
Two cDNA clones homologous with human neuropeptide (NP) Y-Y1
receptor have been isolated from a mouse bone marrow cDNA library. One
was thought to be the cognate of the human NPY-Y1 receptor, termed
Y1 receptor, and the other form, termed Y1
receptor, differed
from the Y1
receptor in the seventh transmembrane domain and
C-terminal tail. Analysis of the mouse genomic DNA showed that both
receptors originated from a single gene. The different peptide
sequences of the Y1
receptor were encoded by separate exons,
hence, these receptors were generated by differential RNA splicing.
High affinity binding of [
I]NPY to each
receptor expressed in Chinese hamster ovary (CHO) cells and
sequestration of [
I]NPY after binding to each
receptor were observed. In the CHO cells expressing the Y1
receptor, intracellular Ca
increase, inhibition of
forskolin-induced cAMP accumulation, and mitogen-activated protein
kinase (MAPK) activation were observed by stimulation of NPY, and these
responses were abolished by pretreatment with pertussis toxin. Since
wortmannin completely inhibited NPY-elicited MAPK activation, we
speculate that wortmannin-sensitive signaling molecule(s) such as
phosphoinositide 3-kinase may lie between pertussis toxin-sensitive
G-protein and MAPK. In contrast, these intracellular signals were not
detected in CHO cells expressing the Y1
receptor. Northern blots
and reverse transcriptase-polymerase chain reaction analyses indicated
that the Y1
receptor was highly expressed in the brain, heart,
kidney, spleen, skeletal muscle, and lung, whereas the Y1
receptor
mRNA was not detected in these tissues. However, the Y1
receptor
was expressed in mouse embryonic developmental stage (7 and 11 days),
bone marrow cells and several hematopoietic cell lines. These results
suggest that the Y1
receptor is an embryonic and a bone marrow
form of the NPY-Y1 receptor, which decreases in the expression during
development and differentiation.
Neuropeptide Y (NPY), ()a 36-amino acid peptide, is
an important regulator in central and peripheral nervous
systems(1) . NPY is highly conserved in primary structure among
species as sequences of human, rabbit, rat, and mouse are identical and
differ from the porcine sequence by only a single amino
acid(2) . It belongs to a peptide family that also includes
peptide YY (PYY) and pancreatic polypeptide (PP)(3) . Mammalian
NPY and PYY show 70% sequence identity, while PP is 50% homologous to
NPY. NPY is widely distributed in the brain (4) and the
peripheral nervous system(5) , and is often co-localized with
norepinephrine, e.g. in sympathetic perivascular nerve
fibers(4, 5) . Studies of various organs and cell
types with peptide fragments of NPY have indicated that multiple NPY
receptor subtypes exist(6) . The two major receptor subtypes
have been designated Y1 and Y2, and the Y1 receptor has the ability to
respond to an analog of NPY modified at residues 31 and 34
([Leu
,Pro
]NPY)(7) . The Y2
receptor subtype is defined on the basis of its affinity to the NPY
peptide C-terminal fragment NPY-(13-36)(8) . More
recently, data from several laboratories have indicated the existence
of a Y3 type receptor to which PYY shows a markedly lower affinity than
NPY(9) . NPY receptors have been identified in a variety of
tissues, including brain, spleen, small intestine, kidney, testis, and
placenta(10, 11, 12) . In addition, binding
sites have been noted in human cell lines such as SK-N-MC cells
(neuroblastoma cell line) and HEL cells (erythroleukemia cell
line)(13, 14) .
NPY mRNA and NPY-like immunoreactivity has been detected in rat megakaryocytes and platelets as well as in preparations of rat mononuclear blood cells(15) . In particular, high levels of NPY mRNA and NPY-like immunoreactivity were found in bone marrow of certain species of autoimmune mice that develop B-cell lymphoproliferative disorders (15, 16) and in bone marrow and peripheral lymphoblasts of children with B-cell precursor leukemia (17) . These results suggest that NPY may function in hematopoietic and/or immune systems, as well as in nervous systems.
Human (18, 19) and rat (20, 21) brain NPY receptor cDNAs were isolated and showed a sequence similar to members of a G-protein coupled receptor superfamily. Ligand-binding characteristics of the expressed protein showed that the cDNA encodes the Y1-type receptor. In addition, the rat Y1-type receptor was demonstrated not only in brain but also in splenic lymphocytes, by means of polymerase chain reaction (PCR) and ligand-binding experiments(22) . However, the signal transduction mechanism through the Y1-type receptor such as mitogen-activated protein kinase (MAPK) activation has not been clarified. We isolated the cognate mouse NPY-Y1 receptor cDNA from a bone marrow cell cDNA library and found a novel receptor form differing in seventh transmembrane and C-terminal tail domains. We describe here the origin of this structural diversity of the cloned mouse NPY-Y1 receptors, and provide novel information on the distribution of mRNAs encoding the two receptor isoforms, and on the cellular signaling of the cloned receptors expressed in Chinese hamster ovary (CHO) cells.
Figure 1: PCR analysis of the human NPY-Y1 receptor mRNA. PCR reaction and hybridization were carried out as described under ``Experimental Procedures.'' Lane 1, smooth muscle; lane 2, brain; lane 3, vascular endothelial cells; lane 4, kidney; lane 5, lung; lane 6, bone marrow cells; and lane 7, leukocytes.
To determine the
functional role of the NPY-Y1 receptor in bone marrow cells, we
isolated and sequenced mouse NPY-Y1 receptors from a mouse bone marrow
cell cDNA library. Upon screening of approximately 5 10
plaques of the bone marrow cell cDNA library, using the human
NPY-Y1 receptor fragment as a probe, we obtained 2 positive clones. One
of the isolated clones, represented by Y1
receptor, has a 2279-bp
insert DNA containing a 1146-bp open reading frame. Since analysis of
the predicted amino acid sequence indicates that the polypeptide
encoded by this cDNA has seven transmembrane regions typical of
G-protein coupled receptors and is 93% homologous to the human NPY-Y1
receptor, it is thought to be the mouse homologue of the NPY-Y1
receptor (Fig. 2A, a and b). The
cytoplasmic tail of this receptor contains 6 serine residues and 4
threonine residues, as possible phosphate acceptors, and as observed in
the human NPY-Y1 receptor. Furthermore, there seem to be four N-linked glycosylation sites in the N-terminal domain and the
extracellular loops.
Figure 2:
The nucleotide and predicted amino acid
sequence of cDNAs of NPY-Y1 and Y1
. A, the common
nucleotide sequence is shown (a), followed by the sequences
specific to each clone ((b) for NPY-Y1
and (c)
for NPY-Y1
). Deduced amino acid are shown in single-letter code.
The seven putative transmembrane domains are indicated by I to VII. The tandemly repeated DNA sequence poly(TG) and poly(CG)
is underlined. B, schematic representation of the
NPY-Y1
and Y1
receptors. Four potential N-glycosylation sites (&cjs0467;) are
marked.
We then characterized the other clone
represented by Y1 receptor. The sequence was identical to the
Y1
receptor from the 5`-untranslated region to the third
extracellular region, but was completely different in the seventh
transmembrane, the cytoplasmic tail and 3`-untranslated region (Fig. 2A, a and c). Addition of
different DNA fragments at position 908 (numbering from the first base
of the coding sequence) of the Y1
receptor created another reading
frame downstream from this junction, which extends the coding region to
a new stop codon located 14 bp downstream. As a consequence, a 79-amino
acid C-terminal fragment of the Y1
receptor was replaced with a
new 4-amino acid fragment in the C-terminal end of the Y1
receptor. Thus, the Y1
receptor does not carry part of the seventh
transmembrane and C-terminal tail (Fig. 2B). To confirm
the existence of two forms of mouse NPY-Y1 receptor in mouse bone
marrow cells, RT-PCR analysis was carried out with template cDNAs
constructed with mRNAs of the bone marrow cells. As shown in Fig. 3, the amplified products corresponding to each clone were
detected. Thus, mRNAs encoding two isoforms of mouse NPY-Y1 receptor
exist in bone marrow cells.
Figure 3: RT-PCR analysis of the two isoforms of NPY-Y1 receptor mRNAs in bone marrow cells. a, schematic presentation of PCR primers, corresponding positions in each cDNA and expected sizes of PCR products. b, gel electrophoresis of amplified products. Lanes 1-5 correspond to PCR analysis with a primer pair of SP2 and aAP2 in lane 1; SP1 and aAP1 in lane 2; SP2 and bAP2 in lane 3; SP2 and bAP1 in lane 4; SP1 and bAP1 in lane 5. c, Southern blot analysis of amplified products. After gel electrophoresis (panel b), DNA products were transferred onto nylon membrane and Southern blots made using an internal DNA fragment (prepared by PCR as described under ``Experimental Procedures'') as a probe (represented by solid bar in a).
Figure 4:
Genomic analysis of the mouse NPY-Y1
receptor gene. a, Southern blot analysis of mouse genomic DNA.
Mouse genomic DNA was digested with BamHI (lane 1), PstI (lane 2), HindIII (lane 3), KpnI (lane 4), or XhoI (lane 5).
Hybridization analysis was carried out as described under
``Experimental Procedures'' with the EcoRI-PstI fragment of NPY-Y1 receptor as a
probe. b, organization of the mouse NPY-Y1 receptor gene and
its relationship to both mRNAs. c, boundary sequences of the
exon/intron. Exon and intron are represented by capital and lower case letters, respectively.
Upon screening of
approximately 1.5 10
plaques of a mouse genomic
library with the above probe (the EcoRI-PstI
fragment), we obtained 5 positive clones. One of the isolated clones
(
MY1
2), approximately 23 kbp, was analyzed in detail.
Restriction mapping of this clone is shown in Fig. 4b.
Partial sequence and Southern blot analysis revealed that this clone
contained the entire Y1
receptor open reading frame, including the
5`- and 3`-untranslated regions (Fig. 2A, a and b, and Fig. 4b), but not the Y1
receptor-specific region (Fig. 2c). The mouse genomic
library was thus rescreened using a DNA probe corresponding to the
Y1
receptor-specific cDNA sequences: at positions 980 to 1300 (320
bases) of the Y1
receptor (Fig. 2A, c).
Screening of approximately 1.5
10
plaques yielded 3
positive clones. One of the isolated clones (
MY1
11),
approximately 13 kbp, was extensively characterized. Restriction
mapping, sequencing of the partial fragments that hybridized to the
probes, and comparison with the both receptor cDNAs allowed for
determination of the intron/exon structure of the NPY-Y1 receptor gene.
As shown in Fig. 4b, the Y1
receptor has at least
two introns. The first intron, approximately 6.4 kbp long, was located
at -147/-148 in the 5`-untranslated region of the Y1
receptor. Since the major transcriptional start points of the mouse
NPY-Y1 receptor were determined at positions -167, -182,
-238, -247, and -263 in the 5`-untranslated
region(33) , the first exon consists of about 20
120 bp.
The second intron (108 bp long) is located just after the proposed
fifth transmembrane domain at position 697. A similar organization
(locations of first and second introns) was observed in the human
NPY-Y1 receptor gene(34) . The Y1
receptor is produced by
RNA splicing of the third intron, more than 15 kbp long, located
downstream from position 908 of the Y1
receptor. Sequences around
the putative junctions are shown in Fig. 4c. These
sequences fit well with the proposed consensus sequences for RNA
splicing. These results taken together indicate that the variation in
C-terminal peptides could be produced by alternative splicing of mRNA
from the single gene encoding the mouse NPY-Y1 receptor. The
(TG)
and (GC)
sequences, alternating
purine/pyrimidine repeat, and the potential left-handed Z-DNA-forming
sequences(35, 36, 37, 38, 39) ,
were found in tracts of up to 50 bp long in the Y1
receptor
3`-untranslated region (Fig. 2b). Although the function
of these sequences is unknown, the potential Z-DNA-forming sequences in
the third intron might play a substantial role for splicing of the
Y1
receptor mRNA.
Figure 5:
Time course of
[I]NPY binding to the CHO-NPY
cells (a) or the CHO-NPY
cells (b). The cell
monolayers were washed and incubated with 1 nM [
I]NPY in the absence or presence of 1
µM NPY (nonspecific binding) for various times at 37
°C. Duplicate cultures were then analyzed for total binding (open circles) or internalized ligand (closed
circles) as described under ``Experimental Procedures.''
In the latter case, cells were treated for an additional 3 min at 4
°C with 200 mM Gly-HCl, pH 3, 200 mM NaCl, and
then cell associated ligand was determined.
To further determine the
functional properties of each receptor, intracellular second messages
were investigated by measuring NPY-evoked intracellular Ca mobility, cAMP accumulation, and MAPK activation in the
transfected cells. Upon addition of NPY (10 nM) to the
CHO-NPY
cells, intracellular Ca
was elevated
(190 ± 28 nM, mean ± S.D., n =
5, Fig. 6A, a) and forskolin (20
µM)-stimulated cAMP accumulation was inhibited (49.5
± 3.4% inhibition, mean ± S.D., n = 4).
The intracellular Ca
response was receptor-dependent,
being elicited by NPY, PYY, and
[Leu
,Pro
]NPY, but not by
NPY-(13-36) (data not shown). Elevation in intracellular
Ca
by NPY, PYY, and
[Leu
,Pro
]NPY was comparable to that
observed with the human NPY-Y1 receptor(18) . A transient
generation of inositol trisphosphate evoked by NPY application, and
NPY-induced intracellular Ca
increase was markedly
suppressed by pretreatment with U-73122 (5 µM), a
phospholipase C inhibitor (40, 41) (data not shown).
When the CHO-NPY
cells were treated with PTX (50 ng/ml, 24 h),
intracellular Ca
increase and inhibition of cAMP
production were abolished (the former shown in Fig. 6A, b, and the latter not shown). This suggests that the Y1
receptor
couples to PTX-sensitive G-protein(s), probably
G
/G
. Several G-protein coupled receptors are
reported to activate the signaling pathway involving MAPK
activation(42) . NPY at 10 nM activated MAPK in the
CHO-NPY
cells (peaked at 3
5 min) (Fig. 6B). Since the NPY-elicited MAPK activation was
completely abolished by PTX treatment (50 ng/ml, 24 h), the NPY
receptor-mediated MAPK activation via PTX-sensitive G-protein(s) (Fig. 6C). Recently, we found that the
platelet-activating factor-stimulated MAPK activation in guinea pig
leukocytes is mediated by Ca
-dependent and
Ca
-independent/wortmannin-sensitive pathways (43) . To determine the pathways of MAPK activation by NPY in
the CHO-NPY
cells, the effect of wortmannin was examined.
Pretreatment of the cells with wortmannin inhibited MAPK activation in
response to NPY, with a half-maximal inhibition observed at an
inhibitor dose of 50-100 nM (data not shown). As shown
in Fig. 6C, 500 nM wortmannin completely
inhibited NPY (10 nM)-elicited MAPK activation. Treatment with
wortmannin, at the concentration used in this experiments, did not
affect intracellular Ca
mobilization (Fig. 6A, c). As shown in Fig. 6, A (panel d) and C, MAPK activity was not inhibited
by the treatment of 20 µM BAPTA/AM (intracellular
Ca
chelator), while it completely abolished the
NPY-induced intracellular Ca
increase. These
observations suggest that the Y1
receptor mediates MAPK activation
via a Ca
-independent but a wortmannin-sensitive
pathway. Wortmannin-sensitive signaling molecules such as
phosphoinositide 3-kinase may lie between MAPK activation and
PTX-sensitive G-protein(s).
Figure 6:
Effect of PTX, wortmannin, and BAPTA/AM
on intracellular Ca increase and MAPK activation in
the CHO-NPY
cells. For experiments using PTX, PTX (50 ng/ml) was
added to the medium 24 h before the assay. Wortmannin treatment and
BAPTA/AM loading were carried out as described(43) . A, representative tracing of intracellular
Ca
mobilization by NPY (10 nM) in the
Fura-2/AM loaded-CHO-NPY
cells. Trace a, control cells; trace b, PTX-treated cells; trace c,
wortmannin-treated cells; trace d, BAPTA/AM-loaded cells. B, activation of MAPK by NPY. Electrophoretic mobility shift
of p42 MAPK detected by immunoblot analysis. The cells were
serum-starved for 20 h before stimulation. After prewarming for 10 min
at 37 °C, the cells were challenged with 10 nM NPY, and
cell lysates were prepared at the indicated times. Lane 1, 0
min; lane 2, 0.5 min; lane 3, 3 min; lane 4,
5 min; and lane 5, 30 min. Detection of MAPK was carried out
as described under ``Experimental Procedures.'' The positions
of MAPK and its phosphorylated form (p-MAPK) are shown by arrows. C, effect of PTX, wortmannin, and BAPTA/AM on
NPY-evoked MAPK activation. Lane 1, non-stimulated cells; lane 2, cells stimulated with 10 nM NPY for 3 min; lanes 3-5, NPY (10 nM)-stimulated cells
pretreated with PTX (lane 3), or with 20 µM BAPTA/AM at 25 °C for 30 min (lane 4), or with 500
nM wortmannin at 37 °C for 10 min (lane 5).
Preincubation conditions are the same as in A. The columns and vertical bars show the mean and S.D.,
respectively.
In contrast, NPY-evoked cell responses
such as intracellular Ca increase, inhibition of cAMP
production, or MAPK activation was not detected in the CHO-NPY
cells, although specific binding of [
I]NPY to
the Y1
receptor was observed (Fig. 7). These results
suggest that the cytoplasmic tail of the Y1
receptor contributes
to G-protein(s) activation.
Figure 7:
Failure of Ca mobilization, inhibition of cAMP production and electrophoretic
mobility shift of p42 MAPK by NPY application to the CHO-NPY
cells. A, representative tracing of intracellular
Ca
mobilization by NPY (10 nM) (Trace
a), PYY (10 nM) (Trace b), or
[Leu
,Pro
]NPY (10 nM) (Trace c) in the Fura-2/AM loaded-CHO-NPY
cells. B, activation of MAPK by NPY. Electrophoretic mobility shift
of p42 MAPK detected by immunoblot analysis. Experimental conditions
were the same as for Fig. 6B. Lane 1, 0 min; lane 2, 0.5 min; lane 3, 3 min; lane 4, 5
min; and lane 5, 30 min. C, analysis of adenylate
cyclase inhibition. The CHO-NPY
cells were incubated at 37 °C
for 10 min with 20 µM forskolin in the presence of the
indicated concentrations of NPY, and then the intracellular cAMP
concentration was determined as described under ``Experimental
Procedures.'' N.S., not significant versus control (p > 0.05, Student's t test).
Figure 8:
Northern blot analysis of the NPY-Y1
and NPY-Y1
receptor mRNAs. Expression of the NPY-Y1
(a) and NPY-Y1
receptor mRNA (b) in various
mouse tissues and embryo. Each lane contains 2 µg of
poly(A)
RNA. In c,
-actin probe was used
as an internal control. Lane 1, heart; lane 2, brain; lane 3, spleen; lane 4, lung; lane 5, liver; lane 6, skeletal muscle; lane 7, kidney; lane 8, testis; lane 9, embryo (7 days); lane 10, embryo
(11 days); lane 11, embryo (15 days); and lane 12,
embryo (17 days).
We report here the isolation of two isoforms of the NPY-Y1
receptor cDNA designated Y1, a mouse homologue of the human NPY-Y1
receptor, and Y1
, a truncated form of Y1
(Fig. 2).
RT-PCR, Southern blots, and genomic DNA analyses show that these two
isoforms are generated from a single gene by alternative RNA splicing.
Despite the lack of seventh transmembrane domain and cytoplasmic
tail, the Y1 receptor shows ligand binding specificities identical
to those of the Y1
receptor. Walker et al.(44) reported that ionic interactions between the
positively charged amino acids of NPY and negatively charged residues
of the human NPY-Y1 receptor are involved in ligand-receptor
interaction. By means of site-directed mutagenesis, substitution of
acidic residues (aspartic acids and glutamic acids) present in the
three extracellular loops of the human NPY-Y1 receptor yielded proteins
unable to bind [
I]NPY. In contrast, deletion of
the 51 residues in the C-terminal tail of the receptor resulted in a
loss of 9 negatively charged residues but had no significant effect on
affinity of the receptor for NPY. They suggested that extracellular
loops of the NPY-Y1 receptor are involved in NPY binding, through ionic
interaction. Since the Y1
receptor has a similar affinity to NPY,
the extracellular loops rather than the seventh transmembrane domain
plays a critical role for the ligand binding. Hunyady et al.(30) showed that PTX-sensitive G
-proteins did not
appear to play a role in endocytosis of angiotensin II
(AT
) receptor, since the receptor showed normal
internalization kinetics in PTX-treated cells. They demonstrated that
endocytosis of the AT
receptor was independent of
agonist-induced signal transduction, and receptor internalization and
activation of phospholipase C led to different structural requirements
of the receptor. Such independence of sequestration and the signal
transduction was observed with the neurotensin receptor (45) .
We propose that the
-type receptor has a functional role for NPY
internalization, since sequestration of [
I]NPY
was observed in the
-type receptor expressed CHO cells after
ligand-receptor binding. Intracellular sequestration of the
NPY-receptor complex might provide a specific message to the cells.
Although the two isoforms show identical ligand affinities, there
are differences in cell signaling properties. The Y1 receptor
elicits a PTX-sensitive intracellular Ca
increase,
inhibition of cAMP accumulation, and MAPK activation, whereas the
Y1
receptor evokes no such responses. Irie et al.(46) reported that the C-terminal tail of prostaglandin-E
EP
subtype receptor was essential for activation of
G-protein. They showed that the C-terminal tail-truncated
prostaglandin-E EP
subtype receptor retained the potential
to form the agonist/receptor/G
-protein ternary complex but
failed to activate G
-protein. Hence, we speculate that the
C-terminal tail of NPY-Y1 receptor contributes to the activation of
G-protein(s). Production of multiple isoforms by alternative splicing
has been noted in the rhodopsin-type receptor family, such as D
dopaminergic receptor (47, 48, 49) ,
prostaglandin-E EP
subtype receptor (50, 51) , thromboxane A
receptor(52) , metabotropic glutamate
receptor(53) , neurokinin-1 receptor(54) , MCP-1
receptor(55) , and somatostatin receptor(56) . All
these receptor isoforms differ only in the third cytoplasmic loop or
C-terminal tail, and these isoforms show no properties of the Y1
receptor: truncated structure and defect of cell signaling.
In
CHO-NPY cells, NPY-induced MAPK activation via PTX-sensitive
G-protein was seen to be mediated by
Ca
-independent/wortmannin-sensitive pathway. Several
G-protein coupled receptors, including the
-adrenergic
receptor(57) , lysophosphatidic acid
receptor(58, 59, 60) , M2 muscarinic
acetylcholine receptor(61) , C5a receptor(62) ,
somatostatin receptor(32, 63) , and
platelet-activating factor receptor(64) , have been shown to
stimulate MAPK activation in various cell types. The signaling pathways
by which these receptors activate MAPK are poorly understood, but there
are several pieces of evidence for both Ras-dependent(57, 58, 59, 60, 61, 62) and
Ras-independent (64, 65, 66) activation of
MAPK. Koch et al.(67) reported that MAPK activation
via PTX-sensitive pathway is mediated by the
subunit of
G
-protein and occurs as a result of ras
activation(67) . Activated Ras can then act as a molecular
switch causing Raf-1 activation, and subsequently leading to
stimulation of MAPK cascade. Here, we obtained evidence that
wortmannin-sensitive signaling molecules such as phosphoinositide
3-kinase may lie between PTX-sensitive G-protein and MAPK activation.
Further experiments are on going to elucidate the target molecules of
wortmannin.
Northern blots and RT-PCR analyses showed tissue- and
development-specific expression of two isoforms of receptor mRNAs. The
Y1 receptor was specifically expressed in the brain, heart,
kidney, spleen, skeletal muscle, lung, bone marrow cells, and several
hematopoietic cell lines. In contrast, the Y1
receptor mRNA was
detected in embryo (7 and 11 days), bone marrow cells, and several
hematopoietic cell lines. The functional role of the Y1
receptor
in embryonic development and hematopoietic system can be further
examined by establishing knock-out mice.
NPY mRNA and NPY-like
immunoreactivity is found not only in autonomic nervous systems and in
the adrenal medulla but also in megakaryocytes/platelets and possibly
mononuclear blood cells in rats. In humans, NPY is present in
lymphocytes and monocytes(68) . A high level of NPY was found
in bone marrow of autoimmune mice with B-cell lymphoproliferative
disorders and in children with B-cell precursor leukemia. These
findings suggest a role for NPY during normal B-cell development and/or
pathologic disorders of B-line cells. The existence of the NPY-Y1 type
receptor in rat splenic lymphocytes was deduced from PCR evidence and
from ligand-binding analyses(22) . The presence of the Y1
and Y1
receptors in bone marrow cells suggests a role for these
receptors in the hematopoietic system.
We have described here the cloning and the elucidation of genomic structure, signal transduction, and tissue distribution of two isoforms of the mouse NPY-Y1 receptor with alternatively spliced C-terminal regions. NPY-Y1 receptors form a novel repertoire of G-protein-coupled receptors that are diversified not only by mediating distinct cell signaling but also by differential expression patterns of individual receptors in mouse tissues. Additional studies on functions and regulation of diverse members of NPY receptors are underway to examine complex physiological responses of NPY in the nervous and hematopoietic systems.
The nucleotide sequence(s) reported in this paper has been submitted to the GenBank(TM)/EMBL Data Bank with accession number(s) D63818 [GenBank]and D63819[GenBank].