TwinsMX: Exploring the Genetic and Environmental Influences on Health Traits in the Mexican Population.

TwinsMX registry is a national research initiative in Mexico that aims to understand the complex interplay between genetics and environment in shaping physical and mental health traits among the country's population. With a multidisciplinary approach, TwinsMX aims to advance our knowledge of the genetic and environmental mechanisms underlying ethnic variations in complex traits and diseases, including behavioral, psychometric, anthropometric, metabolic, cardiovascular and mental disorders. With information gathered from over 2800 twins, this article updates the prevalence of several complex traits; and describes the advances and novel ideas we have implemented such as magnetic resonance imaging. The future expansion of the TwinsMX registry will enhance our comprehension of the intricate interplay between genetics and environment in shaping health and disease in the Mexican population. Overall, this report describes the progress in the building of a solid database that will allow the study of complex traits in the Mexican population, valuable not only for our consortium, but also for the worldwide scientific community, by providing new insights of understudied genetically admixed populations.

Genetic quality: a complex issue for experimental study reproducibility.

Laboratory animal research involving mice, requires consideration of many factors to be controlled. Genetic quality is one factor that is often overlooked but is essential for the generation of reproducible experimental results. Whether experimental research involves inbred mice, spontaneous mutant, or genetically modified strains, exercising genetic quality through careful breeding, good recordkeeping, and prudent quality control steps such as validation of the presence of mutations and verification of the genetic background, will help ensure that experimental results are accurate and that reference controls are representative for the particular experiment. In this review paper, we will discuss various techniques used for the generation of genetically altered mice, and the different aspects to be considered regarding genetic quality, including inbred strains and substrains used, quality check controls during and after genetic manipulation and breeding. We also provide examples for when to use the different techniques and considerations on genetic quality checks. Further, we emphasize on the importance of establishing an in-house genetic quality program.

Mild reproductive impact of a Y chromosome deletion on a C57BL/6J substrain.

A recently reported deletion of about 40 Mb in length between 6.12/6.57 and 46.73/47.31 Mb on the Y chromosome long arm of the C57BL/6JBomTac inbred strain made us closely examine the strain's breeding history and reproductive characteristics. We verified that the two copies of Rbm31y that are present inside the putative deletion were indeed deleted. This inbred strain presents an expected litter size for a C57BL/6 substrain. In vitro fertilization (IVF) efficiency and breeding efficiencies are comparable to those of the C57BL/6NTac substrain; however, the male/female sex ratio in the C57BL/6JBomTac is mildly skewed towards females. There is an increase in the percentage of sperm shape abnormalities found in C57BL/6JBomTac (35%) versus C57BL/6NTac (11%). The most frequent type of sperm abnormality observed is bent heads (19%). Additionally, there is deregulation of several transcripts expressed in the testes. We determined that this mutation arose in the C57BL/6JBomTac Foundation Colony in 2008, and it was completely fixed in the colony by 2009.

The case for genetic monitoring of mice and rats used in biomedical research.

Currently, there is the potential to generate over 200,000 mutant mouse strains between existing mouse strains (over 24,000) and genetically modified mouse embryonic stem cells (over 209,000) that have been entered into the International Mouse Strain Resource Center (IMSR) from laboratories and repositories all over the world. The number of rat strains is also increasing exponentially. These mouse and rat mutants are a tremendous genetic resource; however, the awareness of their genetic integrity such as genetic background and genotyping of these models is not always carefully monitored. In this review, we make a case for the International Council for Laboratory Animal Science (ICLAS), which is interested in promoting and helping academic institutions develop a genetic monitoring program to bring a level of genetic quality assurance into the scientific interchange and use of mouse and rat genetically mutant models.

Scleraxis (Scx) directs lacZ expression in tendon of transgenic mice.

Scleraxis is a transcription factor expressed during early periods of mouse tendon morphogenesis. We have determined that tendon is first clearly present in mouse limb at embryonic day 14.5 (E14.5) and, by in situ hybridization, that scleraxis is expressed in the mouse tendons at E14.5. We have also investigated the regulatory elements that direct scleraxis gene expression to the limb tendons. DNA constructs were engineered such that the lacZ reporter gene was expressed under the control of portions of scleraxis regulatory regions. Transgenic mice carrying these constructs were made and expression of the construct was monitored by staining for beta-galactosidase activity. A construct containing 7 Kbp of 5' flanking sequence, the intron, both exons and 1.8 Kbp of 3' flanking sequence was expressed in a pattern that closely resembled the endogenous scleraxis gene. Mouse embryos carrying this construct expressed lacZ in their limb flexor and extensor tendons at E14.5. The lacZ stain in tendon was readily distinguished from -muscle using an anti-myosin heavy chain antibody to visualize muscle. Deletion of the intron, exons and 3' flanking region did not affect the pattern of tendon expression in the limbs of E14.5 transgenic mice. Additional constructs which deleted 5' flanking sequences up to -355 bp from the published cDNA sequence, showed limb tendon expression that was similar to the endogenous gene. When an additional 160 bp were deleted so that only approximately 200 bp of 5' flanking region was directing lacZ expression, no beta-galactosidase activity was observed in the tendons.

C57BL/6N albino/agouti mutant mice as embryo donors for efficient germline transmission of C57BL/6 ES cells.

We generated C57BL/6NTac mice carrying a tyrosinase loss-of function mutation and a reversion of the nonagouti locus to agouti. This strain has a high superovulation response, allows visual detection of chimeric coat color contribution of C57BL/6 ES-cells and provides a simplified breeding format that generates black G1 offspring of pure inbred C57BL/6 background in one step, providing the ideal host for genetically manipulated C57BL/6 ES cells.

Global gene expression profiles associated with retinoic acid-induced differentiation of embryonal carcinoma cells.

We have evaluated the effects of retinoic acid (RA) treatment of F9 embryonal carcinoma (EC) cells, which induces differentiation into primitive endoderm, on gene expression patterns. F9 cells were exposed to RA in culture, and global expression patterns were examined with cDNA-based microarrays at early (8 hr) and later times (24 hr) after exposure. Of the 1,176 known transcripts examined, we identified 57 genes (4.8%) that were responsive to RA at 8 and/or 24 hr: 35 were induced, 20 were repressed, and 2 were differentially regulated at these time points. To determine if our results were dependent on the array technology employed, we also evaluated the response to RA at 24 hr with oligonucleotide-based arrays. With these more dense arrays (12,488 genes), we identified an additional 353 RA-regulated genes (2.8%): 173 were upregulated and 180 were downregulated. Thus, a total of 410 genes regulated by RA were identified with roughly equivalent numbers induced or repressed. Although the expression of many genes found on both array platforms was consistent, the results for some genes were disparate. Quantitative PCR studies on a subset of these genes supported the results obtained with the cDNA arrays. Our results confirmed the regulation of several known RA-responsive genes and we also identified a number of genes not previously known to be RA-responsive. Those novel genes that were induced presumably contribute to the cellular processes required for a shift from proliferation to differentiation, whereas those new genes that were downregulated may possibly contribute to the maintenance of cell proliferation.

DSCR1 (ADAPT78) lethality: evidence for a protective effect of trisomy 21 genes?

Over the last several years, suggestive evidence has accrued supporting a possible involvement for DSCR1 (ADAPT78) in Down syndrome. Toward testing this, we attempted to generate DSCR1 transgenic mice. Surprisingly, in almost every case, embryonic lethality was observed. In C57Bl/6 mice, DSCR1 human transgene was identified in developing embryos prior to lethality and up to day 9.5. Its mRNA expression was also observed and varied relative to control. In rare instances (twice) where transgenics survived to term, no mRNA expression was observed, suggesting that expression is required for lethality. This lethal phenotype contrasted with, and was surprising in light of, mouse models of Down syndrome where multiple chromosome 21 genes including Dscr1 are overexpressed and survive to term. To explain the seemingly contradictory lethal effect of DSCR1 by itself but not in combination with other trisomy genes, we propose that some trisomy genes (including DSCR1) confer lethality, but others suppress it.