Analysis of the Prokineticin 2 System in a Diurnal Rodent, the Unstriped Nile Grass Rat (Arvicanthis niloticus)

Apr 27, 2005Journal of biological rhythms

Study of the prokineticin 2 system in a daytime-active Nile grass rat

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Abstract

The major transcript variant of Arvicanthis niloticus prokineticin 2 (AnPK2) encodes a 26-residue signal peptide followed by an 81-residue mature peptide.

PK2 RNA levels are rhythmically expressed in the suprachiasmatic nucleus (SCN) of A. niloticus, peaking in the morning.
The mature PK2 peptide is identical among A. niloticus, rats, and mice.
Polymorphic sequences and amino acid substitutions were found in the signal sequence of AnPK2 compared to mouse and laboratory rats.
PKR2 mRNA is expressed in the SCN and paraventricular nuclei of the thalamus and hypothalamus in A. niloticus.
No clear evidence suggests that differences in the PK2 ligand/receptor system are responsible for diurnality in A. niloticus.

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Prokineticin 2 (PK2) is a putative output molecule from the SCN. PK2 RNA levels are rhythmic in the mouse SCN, with high levels during the day, and PK2 administration suppresses nocturnal locomotor activity in rats. The authors examined the PK2 system in a diurnal rodent, Arvicanthis niloticus, to determine whether PK2 or PK2 receptors differ between diurnal and nocturnal species. The major transcript variant of A. niloticus PK2 (AnPK2) encodes a 26-residue signal peptide followed by the presumed mature peptide of 81 residues. Within the grass rat signal sequence, polymorphic sequences and amino acid substitutions were observed relative to mouse and laboratory rats, but the hydrophobic core and cleavage site of the signal sequence were preserved. The mature PK2 peptide is identical among A. niloticus, rat, and mouse. AnPK2 mRNA is rhythmically expressed in the SCN, with peak RNA levels occurring in the morning, preceding peaks of Per1 and Per2 as in mouse SCN. Analysis of prokineticin receptor 2 (PKR2) sequences revealed polymorphisms among the grass rats studied. PKR2 mRNA was expressed in the SCN and paraventricular nuclei of the thalamus and hypothalamus. While further analysis is necessary, there is no clear evidence indicating that a difference in the PK2 ligand/receptor system accounts for diurnality in this rodent species. These data contribute to a growing body of evidence suggesting that the key to diurnality lies downstream of the SCN in A. niloticus.

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Analysis of the Prokineticin 2 System in a Diurnal Rodent, the Unstriped Nile Grass Rat (Arvicanthis niloticus)

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