Identification of a human 5-HT6 receptor variant produced by alternative splicing.

The complexity of the 5-hydroxytryptamine (5-HT) (serotonin) receptor family has been increased by the findings that isoforms or splice variants exist for subtypes such as the 5-HT2B, 5-HT2C, 5-HT4 and 5-HT7 subtypes. Further molecular biological studies in our laboratory have demonstrated that a splice variant of the 5-HT6 receptor exists in the human brain. Experiments performed using a degenerate PCR approach from human caudate cDNA revealed a 5-HT6 receptor clone with a 289 bp deletion of the region coding for transmembrane IV through the third intracellular loop. This deletion produces a frameshift creating a downstream stop codon which results in a truncated protein containing 10 unique amino acids at its carboxyl end. The variant transcript occurs as a result of alternative splicing using an upstream donor site and the acceptor site from the first intron in the 5-HT6 receptor gene. The splicing pattern seen for this transcript was not detected in rat or mouse whole brain cDNA by PCR due to the lack of a consensus 5' donor site. Coexpression of the variant 5-HT6 transcript and the full length 5-HT6 transcript was observed in caudate and substantia nigra but not in hippocampus, cortex, cerebellum and thalamus. Transient transfection of a 5-HT6 variant construct into Cos-7 cells demonstrated that a truncated receptor was translocated to the membrane but appeared nonfunctional.

Characterization of mouse lines transgenic with the human poliovirus receptor gene.

Two mouse lines transgenic with the human poliovirus receptor gene (PVR), TGM-PRG-1 and TGM-PRG-3, were characterized to determine whether transgene copy number and PVR expression levels influence susceptibility to poliovirus. The mouse lines have been bred for more than 10 generations and the transgene was stably transmitted to progeny as determined by Southern blot hybridization and restriction fragment length polymorphism. The transgene copy number is 10 in the TGM-PRG-3 mouse line and one in the TGM-PRG-1 mouse line. Abundance of PVR RNA is on average three-fold higher in TGM-PRG-3 relative to TGM-PRG-1 tissues, and the abundance of the receptor molecule is three-fold higher in TGM-PRG-3 central nervous system tissues compared to TGM-PRG-1 tissues as determined by Western blot analysis. When TGM-PRG-1 and TGM-PRG-3 mice were inoculated intracranially with a neurovirulent type III poliovirus strain, they developed clinical symptoms and CNS lesions characteristic of human poliomyelitis. These results indicate that the PVR gene is expressed as a functional receptor in the CNS of both mouse lines rendering the mice susceptible to poliovirus infection. Even though the two mouse lines have different copy numbers of the transgene and different levels of PVR RNA and protein, they are similar in their susceptibility to poliovirus.

The modulation of the rate of inactivation of the mKv1.1 K+ channel by the beta subunit, Kv beta 1 and lack of effect of a Kv beta 1 N-terminal peptide.

The coexpression of the rat Kv beta 1 subunit with the mouse Kv1.1 (mKv1.1) K+ channel in Chinese hamster ovary cells caused an increase in the rate of inactivation of whole-cell current. Current decayed in a bi-exponential fashion with a fast voltage-dependent and a slower voltage-independent component. The inactivating current component accounted for around 40% of the total outward current. In contrast to previous studies using K+ channel alpha subunits, peptides based on the N-terminal of the Kv beta 1 subunit were unable to mimic the action of the entire subunit. The findings indicate differences between the inactivation induced by the Kv beta 1 subunit and the N-type inactivation mechanism associated with certain rapidly-inactivating cloned K+ channel alpha subunits.

The human serotonin 5-hydroxytryptamine1D receptor pseudogene is transcribed.

An examination of mRNA expression of the serotonin genes encoding both psi 5HT1D alpha and the related 5HT1D alpha, demonstrated that the pseudogene is transcribed, and has a tissue distribution similar to the 5HT1D alpha receptor-encoding gene. This psi 5HT1D alpha transcript is capable of being translated into a polypeptide of only 28 amino acids in length, and the psi 5HT1D alpha pseudogene most likely arose from a gene duplication or transposition event.