Neurokinin B (NKB) is a member of the
tachykinin
(
tac
) family that plays important roles in mammalian growth by modulating prolactin (PRL) synthesis and secretion and causing contraction of the stomach and intestine. However, its potential role in regulating growth of teleosts is less clear. We aimed to explore the role that NKB plays in regulating fish growth using the spotted sea bass (
Lateolabrax maculatus
) as a model. In the present study, two
tac3
and two
tacr3
genes were identified in the spotted sea bass. Sequence analysis showed that two
tac3
transcripts,
tac3a
and
tac3b
, encode four NKBs: NKBa-13, NKBa-10, NKBb-13, and NKBb-10. Expression analysis in different tissues showed that both genes are highly expressed in the brain, stomach and intestine of the spotted sea bass.
In situ
hybridization indicated that the
tac3a
and
tac3b
mRNAs are both localized in several brain regions, such as the telencephalon and hypothalamus, and that
tacr3a
and
tacr3b
are localized in the intestinal villus and gastric gland. To investigate the potential role of NKBs in regulating growth,
in vitro
experiments were performed to detect the effect of NKBs on growth-related gene expression in the brain and brain-gut peptide (BGP)-related genes in the stomach and intestine. NKBb-13 was the most critical ligand in regulating the expression of growth-related genes in the brain and brain-gut peptide (BGP)-related genes in the stomach. The expression of
cholecystokinin
(
cck
) was enhanced by NKBa-13, NKBa-10, and NKBb-10 but not NKBb-13 in the intestine. In general, our results showed that NKBs participate in regulating the growth of spotted sea bass.
Neuropeptide FF (NPFF) is a family member of RF-amide peptides, which are suggested to be involved in the control of vertebrate feeding behavior. However, little is known about the effect of the NPFF peptide on feeding-related processes in basal vertebrates. In this study, four full-length cDNAs,
npff
,
npffr1, npffr2-1
, and
npffr2-2
, were cloned from spotted sea bass and characterized. The conserved NPFF peptide is biologically active because it functionally interacts with different receptors expressed in cultured eukaryotic cells to enhance CRE promoter activity. Tissue distribution analysis showed that the highest
npff
mRNA expression occurred in the telencephalon, hypothalamus, medulla, gonad and muscle, but the
npffr
s mRNAs were mainly distributed within the central nervous system (CNS).
In situ
hybridization (ISH) detected
npff
-expressing cells in several specific regions ranging across the telencephalon and midbrain to the hypothalamus. Incubation of the spotted sea bass conserved NPFF peptide significantly increased the expression of
orexin
(
orx
) and
neuropeptide Y
(
npy
) mRNA and decreased the expression of
leptin
(
lep
),
somatostatin
(
ss
), and
cholecystokinin
(
cck
) mRNA in brain cells. Similarly, the conserved NPFF peptide also heightened the expression of
gastrin
(
gas
),
ghrelin
(
ghrl
), and
motilin
(
mtl
) mRNA and significantly reduced the expression of
cck
mRNA in the intestine and stomach. Taken together, these data suggest that the NPFF peptide may play a stimulating role in regulating feeding-related processes in spotted sea bass.
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