Gene expression tissue-specific patterns

The tissue-specific patterns of expression of the PPAR. isotypes suggested that these proteins have distinct physiological roles, and this was further supported when each was specifically disrupted in mouse gene knockout models. 

The recent identification of a rapidly growing family of p53-related genes calls for caution in the interpretation of the consequences of p53 overexpression on differentiation and development. Because these genes appear to be expressed in a restricted, tissue-specific pattern, it is likely that some of the identified p53 targets may turn out to be physiologic downstream effectors of p73 or p51/p40/ket. 

PPARs belong to a family of nuclear transcription factors that heterodimerize with retinoid X receptors (RXR) and function in a ligand-dependent manner [5]. They can activate transcription through binding peroxisome proliferator activated receptor response elements (direct repeat of AGGTCA spaced by one nucleotide). To date, three different PPAR isoforms a, 5/p, and y (and splice variants) have been identified that are encoded by separate genes. The tissue-specific expression pattern of these transcription factors is indicative of their function in those tissues [6]. 

The expression of FGFs at both the RNA and protein level is generally very low in normal adult tissues peaks of FGF expression often occur in brief phases of embryogenesis. In situ hybridization studies have provided evidence for tissue-specific patterns of FGF mRNA expression in early stages of embryonic development (see Section 4.5). Such spatial and temporal regulation of gene expression correlates well with some of the documented effects of these factors, such as induction of mesoderm (by FGF-2, -3, -4, and other FGFs reviewed by Slack, 1994), or induction of specific primordia such as the limbs (by FGF-2 and -4 reviewed by Niswander et al., 1994 Olwin et al., 1994), the eye (by FGF-1 and -2 reviewed by McAvoy et al., 1991), and the inner ear (by FGF-3 Represa et al., 1991 Mansour, 1994). 

A priori, selective utilization of a linear array of functional promoters could produce tissue-specific patterns of gene expression. The number of genes known to contain multiple promoters is increasing steadily (Barry et al, 1993 Timmusk et al., 1993). Moreover, in certain instances different promoters of a multipromoter gene complex are associated with expression in different tissues (Timmusk et al., 1993). As noted above, both of the clustered promoters described in this report appear to direct expression of NOSl in the cerebellum. However, Marsden et al. (1994) have reported that human NOSl mRNAs with different 5 -terminal exons are expressed outside of the CNS. These mRNAs are likely to be subject to transcriptional control by additional promoters. 

The processing of hnRNA molecules is a site for regulation of gene expression. Alternative patterns of RNA splicing result from tissue-specific adaptive and developmental control mechanisms. As mentioned... 

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