Abstract of related literatures |
1. Lipoprotein lipase (LPL) and hepatic lipase (HL) enzyme activities were previously reported to be regulated during development, but the underlying molecular events are unknown. In addition, little is known about LPL evolution. We cloned and sequenced a complete mouse LPL cDNA. Comparison of sequences from mouse, human, bovine, and guinea pig cDNAs indicated that the rates of evolution of mouse, human, and bovine LPL are quite low, but guinea pig LPL has evolved several times faster than the others. 32P-Labeled mouse LPL and rat HL cDNAs were used to study lipase mRNA tissue distribution and developmental regulation in the rat. Northern gel analysis revealed the presence of a single 1.87 kb HL mRNA species in liver, but not in other tissues including adrenal and ovary. A single 4.0 kb LPL mRNA species was detected in epididymal fat, heart, psoas muscle, lactating mammary gland, adrenal, lung, and ovary, but not in adult kidney, liver, intestine, or brain. Quantitative slot-blot hybridization analysis demonstrated the following relative amounts of LPL mRNA in rat tissues: adipose, 100%; heart, 94%; adrenal, 6.6%; muscle, 3.8%; lung, 3.0%; kidney, 0%; adult liver, 0%. The same quantitative analysis was used to study lipase mRNA levels during development. There was little postnatal variation in LPL mRNA in adipose tissue; maximal levels were detected at the earliest time points studied for both inguinal and epididymal fat. In heart, however, LPL mRNA was detected at low levels 6 days before birth and increased 278-fold as the animals grew to adulthood.(ABSTRACT TRUNCATED AT 250 WORDS) PMID: [2723548]
2. The catabolism of triglycerides-rich lipoproteins and the subsequent uptake of free fatty acids by muscle and adipose tissue is dependent on the enzyme lipoprotein lipase (LPL). To better understand the regulation of this enzyme, we have isolated and characterized the mouse LPL gene. The gene is 28 kb in length and comprises 10 exons which encode a 4.0-kb mRNA. In this report, almost 6 kb of DNA sequence is presented, including 1251 bp 5' to the gene, over 4 kb of exon and exon-intron junctions, and 583 bp 3' to the gene. RNA from differentiated 3T3-L1 adipocytes was used in primer extension and RNase protection assays to show that the 5' untranslated region is not interrupted by an intron and the start site of transcription is 199 bp 5' to the ATG codon that begins translation. The first exon codes for the 5' untranslated region and the signal peptide of 27 amino acids and 2 amino acids of the mature protein, exons 2-9 code for 445 amino acids of the mature protein. These exons are short and vary in length from 102 to 287 bp. The 10th exon codes for the 3' untranslated region and is 2346 bp long. This exon contains a single copy of a B1 repetitive element of 152 bp followed by a 169-bp homopurine stretch. These elements are flanked by a pair of 16-bp direct repeats. The mouse gene is similar in size to the human, which also contains 10 exons in similar locations. There is a high degree of sequence homology between the two genes, 5' region (700 bp), 75%; 5' untranslated region, 74%; coding region, 88%; 3' untranslated region, 75%. The most striking difference is the absence of the B1 repetitive element and homopurine region in the human 3' untranslated region. This information about the mouse LPL gene may lead to a better understanding of its regulation and role in plasma lipoprotein metabolism. PMID: [1765386]
3. This study describes comprehensive polling of transcription start and termination sites and analysis of previously unidentified full-length complementary DNAs derived from the mouse genome. We identify the 5' and 3' boundaries of 181,047 transcripts with extensive variation in transcripts arising from alternative promoter usage, splicing, and polyadenylation. There are 16,247 new mouse protein-coding transcripts, including 5154 encoding previously unidentified proteins. Genomic mapping of the transcriptome reveals transcriptional forests, with overlapping transcription on both strands, separated by deserts in which few transcripts are observed. The data provide a comprehensive platform for the comparative analysis of mammalian transcriptional regulation in differentiation and development. PMID: [16141072]
4. The National Institutes of Health's Mammalian Gene Collection (MGC) project was designed to generate and sequence a publicly accessible cDNA resource containing a complete open reading frame (ORF) for every human and mouse gene. The project initially used a random strategy to select clones from a large number of cDNA libraries from diverse tissues. Candidate clones were chosen based on 5'-EST sequences, and then fully sequenced to high accuracy and analyzed by algorithms developed for this project. Currently, more than 11,000 human and 10,000 mouse genes are represented in MGC by at least one clone with a full ORF. The random selection approach is now reaching a saturation point, and a transition to protocols targeted at the missing transcripts is now required to complete the mouse and human collections. Comparison of the sequence of the MGC clones to reference genome sequences reveals that most cDNA clones are of very high sequence quality, although it is likely that some cDNAs may carry missense variants as a consequence of experimental artifact, such as PCR, cloning, or reverse transcriptase errors. Recently, a rat cDNA component was added to the project, and ongoing frog (Xenopus) and zebrafish (Danio) cDNA projects were expanded to take advantage of the high-throughput MGC pipeline. PMID: [15489334]
5. The bone marrow stroma contains pre-adipocyte cells which are part of the hemopoietic microenvironment. Cloned stromal cell lines differ both in their ability to support myeloid and lymphoid development and in their ability to undergo adipocyte differentiation in vitro. These processes have been examined in the +/+2.4 murine stromal cell line and compared to other stromal and pre-adipocyte cell lines. In long-term cultures, the +/+2.4 stromal cells support myeloid cell growth, consistent with their expression of macrophage-colony stimulating factor mRNA. However, despite the presence of mRNA for the lymphoid supportive cytokines interleukins 6 and 7, +/+2.4 cells failed to support stromal cell dependent B lineage lymphoid cells in vitro, suggesting that these stromal cells exhibit only a myelopoietic support function. The +/+2.4 cells differentiate into adipocytes spontaneously when cultured in 10% fetal bovine serum. The process of adipogenesis can be accelerated by a number of agonists based on morphologic and gene marker criteria. Following induction with hydrocortisone, methylisobutylxanthine, indomethacin, and insulin in combination, a time dependent increase in the steady state mRNA and enzyme activity levels of the following adipocyte specific genes was observed: adipocyte P2, adipsin, CAAT/enhancer binding protein, and lipoprotein lipase. In contrast, adipogenesis was accompanied by a slight decrease in the signal intensity of the macrophage-colony stimulating factor mRNA level, similar to that which has been reported in other bone marrow stromal cell lines. These data demonstrate that although the lympho-hematopoietic support function of pre-adipocyte bone marrow stromal cell lines is heterogeneous, they share a common mechanism of adipogenesis. PMID: [1339460]
6. The enzyme lipoprotein lipase (LPL) is responsible for the hydrolysis of triglycerides into free fatty acids and glycerol. Its synthesis is induced as the murine bone marrow stromal cell clone, BMS2, undergoes adipocyte differentiation. The murine genomic LPL promoter has been cloned, sequenced, and characterized by functional and structural assays. The transcriptional start points have been mapped by S1 nuclease and primer extension techniques. Comparison of the 1.7-kb of LPL 5'-flanking sequence between mouse and man reveals 65% identity or greater with conservation of many potential protein-recognition motifs. Using constructs linking this region to the luciferase-encoding reporter gene, transient transfection experiments have documented the promoter function of this sequence in a number of cell lines. Based on a battery of restriction endonucleases, at least 260 bp immediately adjacent to and including the 5'-untranslated region of the first exon are hypersensitive to exogenous nuclease digestion, consistent with an altered chromatin structure. Protein-DNA interactions are detected within this area at the octamer binding protein 1 site and immediately 5' to the translation initiation site based on ExoIII footprinting and gel retention assays. PMID: [1748295]
7. cDNA clones corresponding to the entire coding region of mature lipoprotein lipase were identified by antibody screening of a mouse macrophage library and sequenced. The predicted amino acid sequence indicates that the mature protein contains 447 amino acids with a molecular weight of 50,314. Comparison of the nucleotide and amino acid sequence with those of rat hepatic lipase and porcine pancreatic lipase reveals extensive homology among the enzymes, indicating that they are members of a gene family of lipases. Most striking is a conservation of five disulfide bridges in all three enzymes, strongly suggesting that the enzymes have similar overall folding patterns. Lipoprotein lipase is also shown to be extraordinarily conserved among mouse, human, and bovine species. The mRNA for lipoprotein lipase is abundant in heart and adipose tissue but is also present in a wide variety of other tissues. There are two major species of mRNA in mouse and human tissues examined, 3.6 and 3.4 kilobases (kb) in size. Rat tissues, on the other hand, contain only the 3.6-kb species while bovine tissues contain an additional 1.7-kb species. PMID: [3597382]
8. The triglycerides in chylomicrons are hydrolyzed by lipoprotein lipase (LpL) along the luminal surface of the capillaries. However, the endothelial cell molecule that facilitates chylomicron processing by LpL has not yet been defined. Here, we show that glycosylphosphatidylinositol-anchored high-density lipoprotein-binding protein 1 (GPIHBP1) plays a critical role in the lipolytic processing of chylomicrons. Gpihbp1-deficient mice exhibit a striking accumulation of chylomicrons in the plasma, even on a low-fat diet, resulting in milky plasma and plasma triglyceride levels as high as 5000 mg/dl. Normally, Gpihbp1 is expressed highly in heart and adipose tissue, the same tissues that express high levels of LpL. In these tissues, GPIHBP1 is located on the luminal face of the capillary endothelium. Expression of GPIHBP1 in cultured cells confers the ability to bind both LpL and chylomicrons. These studies strongly suggest that GPIHBP1 is an important platform for the LpL-mediated processing of chylomicrons in capillaries. PMID: [17403372]
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