Murine endogenous retroviruses and their transcriptional potentials

Identification and classification of feline endogenous retroviruses in the cat genome using degenerate PCR and in silico data analysis

The purpose of this study was to identify and classify endogenous retroviruses (ERVs) in the cat genome. Pooled DNA from five domestic cats was subjected to degenerate PCR with primers specific to the conserved retroviral pro/pol region. The 59 amplified retroviral sequences were used for in silico analysis of the cat genome (Felis_catus-6.2). We identified 219 ERV γ and β elements from cat genome contigs, which were classified into 42 ERV γ and 4 β families and further analysed. Among them, 99 γ and 5 β ERV elements contained the complete retroviral structure. Furthermore, we identified 757 spuma-like ERV elements based on the sequence homology to murine (Mu)ERV-L and human (H)ERV-L. To the best of our knowledge, this is the first detailed genome-scale analysis examining Felis catus endogenous retroviruses (FcERV) and providing advanced insights into their structural characteristics, localization in the genome, and diversity.

Mutations in LMF1 cause combined lipase deficiency and severe hypertriglyceridemia

Hypertriglyceridemia is a hallmark of many disorders, including metabolic syndrome, diabetes, atherosclerosis and obesity. A well-known cause is the deficiency of lipoprotein lipase (LPL), a key enzyme in plasma triglyceride hydrolysis. Mice carrying the combined lipase deficiency (cld) mutation show severe hypertriglyceridemia owing to a decrease in the activity of LPL and a related enzyme, hepatic lipase (HL), caused by impaired maturation of nascent LPL and hepatic lipase polypeptides in the endoplasmic reticulum (ER). Here we identify the gene containing the cld mutation as Tmem112 and rename it Lmf1 (Lipase maturation factor 1). Lmf1 encodes a transmembrane protein with an evolutionarily conserved domain of unknown function that localizes to the ER. A human subject homozygous for a deleterious mutation in LMF1 also shows combined lipase deficiency with concomitant hypertriglyceridemia and associated disorders. Thus, through its profound effect on lipase activity, LMF1 emerges as an important candidate gene in hypertriglyceridemia.

Rmcf2, a xenotropic provirus in the Asian mouse species Mus castaneus, blocks infection by polytropic mouse gammaretroviruses

Cells from the Asian wild mouse species Mus castaneus are resistant to infection by the polytropic host range group of mouse gammaretroviruses. Two factors are responsible for this resistance: a defective XPR1 cell surface receptor for polytropic murine leukemia viruses (P-MLVs), and a resistance factor detectable only in interspecies hybrids between M. castaneus and mice with an XPR1 variant that permits infection by xenotropic MLVs (X-MLVs) as well as P-MLVs. This second novel virus resistance phenotype has been associated with expression of viral Env glycoprotein; Northern blotting with specific hybridization probes identified a spliced X-MLV env message unique to virus-resistant mice. These observations suggest that resistance is due to expression of one or more endogenous X-MLV envelope genes that interfere with infection by exogenous P-MLVs. M. castaneus contains multiple X-MLV proviruses, but serial backcrosses reduced this proviral content and permitted identification of a single proviral env sequence inherited with resistance. The resistance phenotype and the provirus were mapped to the same site on distal chromosome 18. The provirus was shown to be a full-length provirus highly homologous to previously described X-MLVs. Use of viral pseudotypes confirmed that this resistance gene, termed Rmcf2, prevents entry of P-MLVs. Rmcf2 resembles the virus resistance genes Fv4 and Rmcf in that it produces Env glycoprotein but fails to produce infectious virus; the proviruses associated with all three resistance genes have fatal defects. This type of provirus Env-mediated resistance represents an important defense mechanism in wild mouse populations exposed to endemic infections.