Endogenous retroviruses are implicated in the pathogenesis of systemic lupus erythematosus (SLE). Because four different classes of endogenous retroviruses, i.e., ecotropic, xenotropic, polytropic, or modified polytropic (mPT), are expressed in mice, we investigated the possibility that a particular class of endogenous retroviruses is associated with the development of murine SLE. We observed >15-fold increased expression of mPT env (envelope) RNA in livers of all four lupus-prone mice, as compared with those of nine nonautoimmune strains of mice. This was not the case for the three other classes of retroviruses. Furthermore, we found that in addition to intact mPT transcripts, many strains of mice expressed two defective mPT env transcripts which carry a deletion in the env sequence of the 3 portion of the gp70 surface protein and the 5 portion of the p15E transmembrane protein, respectively. Remarkably, in contrast to nonautoimmune strains of mice, all four lupus-prone mice expressed abundant levels of intact mPT env transcripts, but only low or nondetectable levels of the mutant env transcripts. The Sgp3 (serum gp70 production 3) locus derived from lupus-prone mice was responsible for the selective up-regulation of the intact mPT env RNA. Finally, we observed that single-stranded RNA-specific TLR7 played a critical role in the production of anti-gp70 autoantibodies. These data suggest that lupus-prone mice may possess a unique genetic mechanism responsible for the expression of mPT retroviruses, which could act as a triggering factor through activating TLR7 for the development of autoimmune responses in mice predisposed to SLE.

The endogenous retroviral envelope glycoprotein, gp70, implicated in murine lupus nephritis is secreted by hepatocytes as an acute phase protein, and it has been thought to be a product of an endogenous xenotropic virus, NZB-X1. However, since endogenous polytropic (PT) and modified polytropic (mPT) viruses encode gp70s that are closely related to xenotropic gp70, these viruses can be additional sources of serum gp70. To better understand the genetic basis of the expression of serum gp70, we analyzed the abundance of xenotropic, PT, or mPT gp70 RNAs in livers and the genomic composition of corresponding proviruses in various strains of mice, including two different Sgp (serum gp70 production) congenic mice. Our results demonstrated that the expression of different viral gp70 RNAs was remarkably heterogeneous among various mouse strains and that the level of serum gp70 production was regulated by multiple structural and regulatory genes. Additionally, a significant contribution of PT and mPT gp70s to serum gp70 was revealed by the detection of PT and mPT, but not xenotropic transcripts in 129 mice, and by a closer correlation of serum levels of gp70 with the abundance of PT and mPT gp70 RNAs than with that of xenotropic gp70 RNA in Sgp3 congenic mice. Furthermore, the injection of lipopolysaccharides selectively up-regulated the expression of xenotropic and mPT gp70 RNAs, but not PT gp70 RNA. Our data indicate that the genetic origin of serum gp70 is more heterogeneous than previously thought, and that distinct retroviral gp70s are differentially regulated in physiological vs inflammatory conditions.

We established the mutant mouse line, B6;CB-Skt GtAyu8021IMEG (Skt Gt ), through gene-trap mutagenesis in embryonic stem cells. The novel gene identified, called Sickle tail (Skt), is composed of 19 exons and encodes a protein of 1352 amino acids. Expression of a reporter gene was detected in the notochord during embryogenesis and in the nucleus pulposus of mice. Compression of some of the nuclei pulposi in the intervertebral discs (IVDs) appeared at embryonic day (E) 17.5, resulting in a kinky-tail phenotype showing defects in the nucleus pulposus and annulus fibrosus of IVDs in Skt Gt/Gt mice. These phenotypes were different from those in Danforth's short tail (Sd) mice in which the nucleus pulposus was totally absent and replaced by peripheral fibers similar to those seen in the annulus fibrosus in all IVDs. The Skt gene maps to the proximal part of mouse chromosome 2, near the Sd locus. The genetic distance between them was 0.95 cM. The number of vertebrae in both [Sd 1/1 Skt Gt ] and [Sd Skt Gt /1 1] compound heterozygotes was less than that of Sd heterozygotes. Furthermore, the enhancer trap locus Etl4 lacZ , which was previously reported to be an allele of Sd, was located in the third intron of the Skt gene. T HE notochord is an integral component of the axial structure of vertebrates, functions as a signaling center during embryogenesis, and plays essential roles in patterning of both somites and the neural tube (Ang and Rossant 1994; Wilson et al.1995; Chiang et al.1996). In addition, the notochord has major roles in vertebral column formation. In the mouse, the notochord is a continuous rod of constant diameter extending from the hypophysis to almost the tip of the tail at embryonic day (E) 9.5. At E10.5-E11.5, signals from the notochord induce the migration, proliferation, and fusion of the sclerotome to form a continuous and unsegmented perichordal tube around the notochord and neural tube. At 12.5, mesenchyme acquires a characteristic metameric pattern of densely packed areas caudally and loosely packed areas cranially. Some densely packed cells move cranially and give rise to the annulus fibrosus of the future intervertebral disc (IVD). The remaining densely packed cells fuse with the immediately caudal loosely packed cells to form the cartilaginous primordia of the vertebral bodies. Notochord cells located in the vertebral body of cranial regions start to relocate into intervertebral regions (Paavola et al. 1980;Rufai et al. 1995;Aszodi et al. 1998). At E13.5, the vertebral regions are enlarged and chondrified. The notochord proliferates and undergoes hypertrophy to form the gelatinous center of the intervertebral disc, called the nucleus pulposus. This nucleus is surrounded by the circularly arranged fibers of the annulus fibrosus. These two structures together constitute the IVD (Langman 1969;Theiler 1988 intervertebral regions. Failures in somite, neural tube, and notochord formation are closely correlated with vertebral malformations. However, the mechanisms that underlie the formatio...

The previously isolated cDNA encoding human adenylate kinase (AK) isozyme 3 was recently renamed AK4. Consequently, human AK3 cDNA remains to be identified and we have little information about the functional relationship between human AK3 and AK4. In pursuit of the physiological roles of both the AK3 and AK4 proteins, we first isolated an authentic human AK3 cDNA and compared their expression. Nucleotide sequencing revealed that the cDNA encoded a 227-amino-acid protein, with a deduced molecular mass of 25.6 kDa, that shares greater homology with the AK3 cDNAs isolated from bovine and rat than that from human. We named the isolated cDNA AK3. Northern-blot analysis revealed that AK3 mRNA was present in all tissues examined, and was highly expressed in heart, skeletal muscle and liver, moderately expressed in pancreas and kidney, and weakly expressed in placenta, brain and lung. On the other hand, we found that human AK4 mRNA was highly expressed in kidney, moderately expressed in heart and liver and weakly expressed in brain. Western-blot analysis demonstrated expression profiles of AK3 and AK4 that were similar to their mRNA expression patterns in each tissue. Over expression of AK3, but not AK4, in both Escherichia coli CV2, a temperature-sensitive AK mutant, and a human embryonic kidney-derived cell line, HEK-293, not only produced significant GTP:AMP phosphotransferase (AK3) activity, but also complemented the CV2 cells at 42 degrees C. Subcellular and submitochondrial fractionation analysis demonstrated that both AK3 and AK4 are localized in the mitochondrial matrix.

Background: Hox genes encode transcription factors which are involved in the establishment of regional identities along the anteroposterior (AP) body axis. To elucidate the AP patterning of the digestive tract, we have systematically examined the expression patterns of Hox genes belonging to paralogue groups 6, 7, 8 and 9 by whole-mount in situ hybridization and by section in situ hybridization analyses.