RNA splice variants

Adult Purkinje cells strongly express the NRl gene (Watanabe et al., 1994 Cull-Candy et al., 1998). All the NRl RNA splice variants are found, although NRl-3 (Cl only, see Fig. 6) RNA is at low levels (Laurie et al., 1995). However, according to most reports, adult Purkinje cells do not contain NR2-type subunit mRNA (Watanabe et al., 1994), and indeed have no detectable NMDA receptors (Cull-Candy et al., 1998) nevertheless, two groups have described NR2A mRNA in Purkinje cells (Akazawa et al., 1994 Luque and Richards, 1995). This has still not been resolved. The mismatch in expression between NRl and the NR2 series has been much commented on (Cull-Candy et al., 1998), and it is indeed unusual to find a neuron type with no NMDA response. An outside possibility is that the NRl subunit... 

Genetic regulation via splice variants and RNA editing further increases receptor heterogeneity the flip/flop versions and the Q/R site 279... 

Genetic regulation via splice variants and RNA editing further increases receptor heterogeneity the flip/flop versions and the Q/R site. Splice variants that impart functional differences and/or different cellular expression patterns have been found for most of the glutamate receptor subunits. The first splice variants to be described were the so-called flip and flop versions of the AMPA... 

Given this combination of internal and C-terminus splice variants and site-specific RNA editing, it appears that four to eight or more mature RNAs can be made from each of the 16 known genes encoding mammalian... 

Figure 9. Some factor secreting mutants expresses CSF-1 transcripts. Northern blot analysis. 12mg of total RNA/lane were analyzed. The major transcript was a 4.0 kb CSF-1 message. Results for parental Myl D7 cells, stroma dependent subclones derived and stroma independent mutants are shown 1, 3i-l 2, 5i-l 3, 6i-4 4, 61-5 5, 31-2 6, 4i-l 7, 5i-3 8, 6i-2 9, 6i-3 10, 6i-17 11, 6i-18 12, 6i-19 13, 6i-20 14, 61-21 15, 6i-22 16, 6i-23 17, 6i-26. Those stroma independent mutants that are secretors are also indicated. Although additional CSF-1 specific splice variants could be detected at low levels in MS-5 and Myl-D7 mutants with high CSF-1 expression, no mutant/cell line specific splice product could be shown. However, the size of the splice product detected depended on the probe that was used for hybridization. Two additional messages (3.2 kb and 2.3 kb) were detected by hybridization with a full length CSF-1 cDNA and only one additional message (2.3kb) was detected by hybridization with a 3 fragment of the cDNA.

In the case of neuropeptides, presynaptic neurotransmission synthesis occurs only in the cell body because the complex machinery for neuropeptide synthesis is not transported into the axon terminal. Synthesis of a specific neuropeptide begins with the pre-propeptide gene in the cell nucleus (Fig. 1 —9). This gene is transcribed into primary ribonucleic acid (RNA), which can be rearranged, or edited, to create different versions of RNA, known as alternative splice variants, such as prepropeptide RNA. 

FIGURE 1—9- Neurotransmitter synthesis in a neuropeptidergic neuron. Neurotransmitter synthesis occurs only in the cell body because the complex machinery for neuropeptide synthesis is not transported into the axon terminal. Synthesis of a specific neuropeptide begins with the transcription of the pre-propeptide gene in the cell nucleus into primary RNA, which can be rearranged or edited to create different versions of RNA, known as alternative splice variants or pre-propeptide RNA. Next, RNA is translated into a pre-propeptide, which enters the endoplasmic reticulum, where its peptide tail is clipped off by an enzyme called a signal peptidase to form the propeptide, the direct precursor of the neuropeptide neurotransmitter. Finally, the propeptide enters synaptic vesicles, where it is converted into the neuropeptide itself. Synaptic vesicles loaded with neuropeptide neurotransmitters are transported down to the axon terminals, where there is no reuptake pump for neuropeptides. The action of peptides is terminated by catabolic peptidases, which cut the peptide neurotransmitter into inactive metabolites. 

FIGURE 5—68. Substance P neurons and neurokinin 1 receptors, part 1. For neurons utilizing substance P, synthesis starts with the gene called pre-protachykinin A (PPT-A). This gene is transcribed into RNA, which is then edited to form three alternative mRNA splice variants, alpha, beta, and gamma. The actions of the mRNA version called alpha-PPT-A mRNA are shown here. This mRNA is then transcribed into a protein called alpha-PPT-A, which is substance P s grandparent. It is converted in the endoplasmic reticulum into the parent of substance P, called protachykinin A (alpha-PT-A). Finally, this protein is clipped even shorter by another enzyme, called a converting enzyme, in the synaptic vesicle and forms substance P itself. 

Berthele, A., Laurie, D. J., Platzer, S., Zieglgansberger, W., Tolle, T. R., and Sommer, B. (1998). Differential expression of rat and human type I metabotropic glutamate receptor splice variant messenger RNAs. Neuroscience 85, 733-749. 

Additional sequence diversity is provided by RNA editing in some subclasses of 5-HT receptors, and numerous single-nucleotide polymorphisms (SNPs) and splice variants are known to exist in many subclasses of these receptors. Editing of 5-HT receptors will be reviewed in this chapter, and SNPs and splice variants will be reviewed in subsequent chapters. 

Wang Q, O Brien PJ, Chen CX, Cho DS, Murray JM, Nishikura K. Altered G protein-coupling functions of RNA editing isoform and splicing variant sero-tonin2C receptors. J Neurochem 2000 74 1290-1300. 

Several possible splice variants of the 5-HT6 receptor have been described, but the functional significance of those variants of 5-HT6 receptors has not been established (354,374). Messenger RNA for at least one of the splice variant is expressed in the human caudate, although transfection studies into COS-7 cells demonstrated membrane expression of the truncated protein, without apparent function (374). 

It is well-established that Hyal-1 is a candidate tumor suppressor gene (TSG) product, detected in many tobacco-related lung tumors,117,118 as well as of the oral cavity and upper airways.119 This occurs not only at the level of DNA, by homozygous deletion or loss of heterozygosity, but also at the level of RNA. Two splice variants coding for Hyal-1 are transcribed, one variant containing a retained intron that is unable to be translated.119 The versatility of the cancer cell is such that any mechanism that eliminates an unwanted activity will be used. 

Bianchi P, Zanella A, Alloisio N, Barosi G, Bredi E et al (1997) A variant of the EPB3 gene of the anti-Lepore type in hereditary spherocytosis. Br J Haematol 98 283-288 Black DL (2003) Mechanisms of alternative pre-messenger RNA splicing. Annu Rev Biochem 72 291-336... 

Monsma, J., F.J. McVittie, L.D. Gerfen, C.R. Mahan, L.C. Sibley, D.R. (1989) Multiple D2 dopamine receptors produced by alternative RNA splicing. Nature 342, 926-929. O Malley, K.L. Mack, K.J. Gandelman, K.Y. Todd, K.D. (1990) Organization and expression of the rat D2A receptor gene identification of alternative transcripts and a variant donor splice site. Biochemistry 29, 1367-1371. 

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