Loss of HtrA2/Omi activity in non-neuronal tissues of adult mice causes premature aging.

mnd2 mice die prematurely as a result of neurodegeneration 30-40 days after birth due to loss of the enzymatic activity of the mitochondrial quality control protease HtrA2/Omi. Here, we show that transgenic expression of human HtrA2/Omi in the central nervous system of mnd2 mice rescues them from neurodegeneration and prevents their premature death. Interestingly, adult transgenic mnd2 mice develop accelerated aging phenotypes, such as premature weight loss, hair loss, reduced fertility, curvature of the spine, heart enlargement, increased autophagy, and death by 12-17 months of age. These mice also have elevated levels of clonally expanded mitochondrial DNA (mtDNA) deletions in their tissues. Our results provide direct genetic evidence linking mitochondrial protein quality control to mtDNA deletions and aging in mammals.

PCR identification of class I major histocompatibility complex genes transcribed in mouse blastocyst and placenta.

We used an RT-PCR based strategy to amplify, clone and sequence MHC class I genes transcribed in the blastocyst and placenta of BALB/c mice. The PCR primers used were capable of amplifying many novel class I sequences from genomic DNA. By comparing the resulting sequence data with known class I sequences, we identified a number of different class I genes transcribed in these tissues. These include H2-K, -D, -L and a novel sequence in blastocysts, and H2-K, -D, -L, -D2, -T9, -T13, -T17, -T18, -M2 and three additional novel sequences in placenta. We postulate that some members of this spectrum of blastocyst and placentally-expressed MHC class Ib genes may act together at the maternal-fetal interface in ways that are important for a successful pregnancy.

A new major histocompatibility complex class I b gene expressed in the mouse blastocyst and placenta.

Because of the role major histocompatibility complex (MHC) class I b molecules may play during mouse embryonic development, we thought it would be interesting to search for additional MHC class I b molecules that might be expressed in preimplantation embryos, and in particular in the trophoblastic lineage. We therefore screened a mouse preimplantation blastocyst cDNA library for MHC class I sequences. This search led to the identification and characterization of a new MHC class I b gene, blastocyst MHC. Sequences identical to the exons and 3' untranslated region of this gene have been found in many laboratory mouse strains, as well as in the related mouse species Mus spreciligus. The presence of this gene in mouse strains of different MHC class I haplotypes argues that blastocyst MHC is a unique, newly-described gene rather than a new allele of a previously described mouse MHC class I gene. Blastocyst MHC has the structure of an MHC class I b gene, with the six exons characteristic of T-region genes. It is linked to H2-D. The amino acid sequence encoded by this gene maintains all the features of a functional antigen-presentation domain. The blastocyst MHC gene, like the human class I b gene HLA-G, is expressed at the blastocyst stage and in the placenta, and may be the mouse analog for HLA-G.

Clinical teratology.

Genetic causes account for 20% to 25% of human birth defects, but the largest proportion of birth defects have no definitive etiology and some of these malformations may be due to intrinsic, "nonpreventable" spontaneous errors of development. Environmental causes, which include maternal disease states, maternal infection, mechanical factors, problems of constraint, chemicals, drugs, and physical agents, are responsible for only about 10% of human birth defects. The scientific basis for understanding the risk of congenital malformations from exposure to environmental agents is based on several tenets of toxicology and embryology dogma. The first tenet is that essentially all teratogens that have been studied have a typical toxicologic dose response relationship and a no-effect dose. Secondly, the stage of gestation is critical to the effects that are expected, and all stages of embryogenesis and fetogenesis can have vulnerability to environmental toxicants. Thirdly, the response of the embryo and fetus is characteristic for each teratogenic agent, although there is some similarity in the effect of certain teratogens. Appropriately designed developmental toxicology studies and basic embryologic and biologic concepts are all used to estimate the potential reproductive hazard for embryonic death, growth retardation, congenital malformation, and functional deficit.

The production of transgenic mice by embryo microinjection.

The production of transgenic mice is a technology of great utility in the dissection of complex biological processes. This article is intended as a detailed primer for people interested in learning to produce transgenic mice, and discusses equipment, methods, and future directions for this technique.

Lens-specific expression of recombinant ricin induces developmental defects in the eyes of transgenic mice.

An expression system for cell lineage ablation in transgenic mice was constructed in which a modified form of the A subunit of ricin, a toxic lectin produced by the castor bean Ricinus communis, can be expressed under the direction of tissue-specific regulatory signals. A chimeric gene was formed by fusing the promoter and 5'-flanking sequences of the lens-specific mouse alpha A-crystallin gene with a modified ricin A cDNA, and this construction was integrated into the germ line of transgenic mice. These animals develop profound microphthalmia with severe developmental defects of the eye, relating primarily to the disorganization and death of cells forming the lens. In addition, this defect is associated with several abnormalities, including eye size, folding of the retina, and ectopic lens material in other regions of the eye. The phenotype of this engineered developmental mutation suggests that the normal development of alpha A-crystallin-producing lens fiber cells is essential for the proper growth, organization, and orientation of optic structures.

A lymphoproliferative abnormality associated with inappropriate expression of the Thy-1 antigen in transgenic mice.

The Thy-1 antigen is a cell-surface glycoprotein of unknown function expressed on mouse T lymphocytes, neurons, and hematopoietic stem cells. To alter the normal pattern of Thy-1 expression during hematopoietic differentiation, we created transgenic mice using a hybrid Thy-1 gene containing a transcriptional enhancer of the mouse immunoglobulin heavy chain gene (E mu). Strains of mice bearing the Thy-1.2/E mu gene express the Thy-1.2 antigen on mature B lymphocytes and their progenitors, and develop a heritable lymphoid hyperplasia characterized by massive expression of the Thy-1.2 antigen in the bone marrow and lymph nodes. The phenotype associated with inappropriate developmental regulation of the Thy-1 gene suggests that the Thy-1 antigen may play a role in inducing activation or differentiation events on early lymphocyte progenitor cells.

Neonatal hyperthyroidism impairs epinephrine-provoked secretion of nerve growth factor and epidermal growth factor in mouse saliva.

We examined long-term effects of neonatal hyperthyroidism on salivary secretions of nerve growth factor and epidermal growth factor in male and female mice at the age of 31 days. Hyperthyroidism was induced by thyroxine (T4) injections (0.4 microgram/g body weight/day) during days 0-6. Littermate control mice were treated with vehicle. T4 treatment did not alter the amounts of protein secreted into saliva but hormone administration induced alteration in the types of protein secreted. T4 treatment decreased the contents of both nerve growth factor and epidermal growth factor secreted into the saliva. A Sephadex G-200 column chromatographic profile revealed the presence of two distinct nerve growth factor immunoreactive peaks, while epidermal growth factor immunoreactivity predominantly eluted as a single low molecular weight form. T4 treatment did not alter the molecular nature of their secretion, but the treatment decreased their contents. These results indicate an impairment in salivary secretion of nerve growth factor and epidermal growth factor long after T4 treatment has been discontinued.

DNA rearrangements of the actin gene cluster in Caenorhabditis elegans accompany reversion of three muscle mutants.

We present evidence that associates dominant mutations in Caenorhabditis elegans that disrupt muscle structure and motility with a cluster of three actin genes mapped in the same region of linkage group V. We examined spontaneous and mutagen-induced wild-type revertants of these dominant alleles for alterations in the DNA of the actin gene cluster. Four of 73 revertants contain detectable DNA rearrangements within the cluster of actin genes including an insertion, a deletion and gene fusions. We postulate that these rearrangements inactivate or delete at least one gene in the cluster and consequently the original mutations are within the actin gene cluster.