International Mammalian Genome Society


The 13th International Mouse Genome Conference
October 31-November 3, 1999

Table of Contents * Structure * Bioinformatics * Sequence * Mapping * New Tools * Gene Discovery * Developmental * Mutagenesis * Functional Genomics

F21 Genomic Characterization and Targeted Mutagenesis of Lysophosphatidic Acid Receptor Genes (lpA1/lpA2/lpA3)

James J. A. Contos and Jerold Chun. Department of Pharmacology, School of Medicine, University of California at San Diego, La Jolla, CA 92093-0636.

Lysophosphatidic acid (LPA) is a normal metabolite of lipid biosythesis that also acts as an extracellular signalling molecule on most cell types, stimulating a variety of responses which can broadly be grouped as proliferative, morphological (acute neurite retraction, stress fiber formation), and biochemical (Ca++/Cl- channel opening, serum response element activation). The lysophospholipid receptor A1 gene (lpA1, also called vzg-1/Edg-2/Gpcr26/mrec1.3) was the first identified G-protein coupled receptor (GPCR) for the lysophosphatidic acid (LPA) and is expressed in embryonic cerebral cortical neuroblasts, postnatal myelinating glia, and various adult tissues (most prominently testes). Two additional putative LPA receptor genes, each encoding proteins approximately 50% identical to LPA1, were identified by searching GenBank (lpA2) or using degenerate PCR on neocortical cell line cDNA (lpA3). Comparative expression analysis revealed that all three are abundantly expressed in adult testes, with lower levels in kidney and lung. Each is expressed in brain at some point in development. Complete cDNA sequences of lpA1-3 were determined using 5'- and 3'-RACE. Genomic clones were isolated and characterized, revealing that each gene shares a unique conserved intron located within coding region for transmembrane domain VI. Though multiple promoters direct transcription of lpA1, both lpA2 and lpA3 have only one. Chromosomal locations of each have been mapped in Mus musculus using a backcross panel from The Jackson Lab: lpA1 is on proximal chromosome 4 at the vacillans (vc) locus, lpA2 is at central chromosome 8 by myodystophy (myd), and lpA3 is located at central chromosome 3 near varitint waddler (va). Exon 4 of the lpA1 gene is duplicated on chromosome 6 in Mus spretus. Using homologous recombination, we have generated mice with deletions in lpA1, lpA2, or lpA3. Approximately half of lpA1(-/-) mice die perinatally, most from a lack of feeding, though some embryos were observed with exencephaly or a frontal haemhorrage. Surviving lpA1(-/-) mice have reduced total body mass and a craniofacial defect. The possibility that mutations in lpA1 might be responsible for vc will be discussed. Preliminary analysis of lpA2 and lpA3 mutant mice will also be presented. Supported by the NIMH, and a grant from Allelix Biopharmaceuticals.

 


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