Brian J. Nieman

A Gja1 missense mutation in a mouse model of oculodentodigital dysplasia.

Oculodentodigital dysplasia (ODDD) is an autosomal dominant disorder characterized by pleiotropic developmental anomalies of the limbs, teeth, face and eyes that was shown recently to be caused by mutations in the gap junction protein alpha 1 gene (GJA1), encoding connexin 43 (Cx43). In the course of performing an N-ethyl-N-nitrosourea mutagenesis screen, we identified a dominant mouse mutation that exhibits many classic symptoms of ODDD, including syndactyly, enamel hypoplasia, craniofacial anomalies and cardiac dysfunction. Positional cloning revealed that these mice carry a point mutation in Gja1 leading to the substitution of a highly conserved amino acid (G60S) in Cx43. In vivo and in vitro studies revealed that the mutant Cx43 protein acts in a dominant-negative fashion to disrupt gap junction assembly and function. In addition to the classic features of ODDD, these mutant mice also showed decreased bone mass and mechanical strength, as well as altered hematopoietic stem cell and progenitor populations. Thus, these mice represent an experimental model with which to explore the clinical manifestations of ODDD and to evaluate potential intervention strategies.

Multiple mouse biological loading and monitoring system for MRI

The use of mice to study models of human disease has resulted in a surge of interest in developing mouse MRI. The ability to take 3D, high‐resolution images of live mice allows significant insight into anatomy and function. However, with imaging times on the order of hours, high throughput of specimens has been problematic. To facilitate high throughput, concurrent imaging of multiple mice has been developed; however, this poses further complexities regarding the ease and rapidity of loading several animals. In this study, custom‐built equipment was developed to streamline the preparation process and to safely maintain seven mice during a multiple‐mouse imaging session. Total preparation time for seven mice was ∼24 min. ECG and temperature were monitored throughout the scan and maintained by regulating anesthetic and heating. Proof of principle was demonstrated in a 3‐h imaging session of seven mice. Magn Reson Med 52:709–715, 2004.

In vivo multiple-mouse MRI at 7 Tesla

We developed a live high‐field multiple‐mouse magnetic resonance imaging method to increase the throughput of imaging studies involving large numbers of mice. Phantom experiments were performed in 7 shielded radiofrequency (RF) coils for concurrent imaging on a 7 Tesla MRI scanner outfitted with multiple transmit and receive channels to confirm uniform signal‐to‐noise ratio and minimal ghost artifacts across images from the different RF coils. Grid phantoms were used to measure image distortion in different positions in the coils. The brains of 7 live mice were imaged in 3D in the RF coil array, and a second array of 16 RF coils was used to 3D image the whole bodies of 16 fixed, contrast agent‐perfused mice. The images of the 7 live mouse brains at 156 μm isotropic resolution and the 16 whole fixed mice at 100 μm isotropic resolution were of high quality and free of artifacts. We have thus shown that multiple‐mouse MRI increases throughput for live and fixed mouse experiments by a factor equaling the number of RF coils in the scanner. Magn Reson Med, 2005.

Retrospective gating for mouse cardiac MRI.

Cardiac MR imaging in small animals presents some difficulties due to shorter cardiac cycles and smaller dimensions than in human beings, but prospectively gated techniques have been successfully applied. As with human imaging, there may be certain applications in animal imaging for which retrospective gating is preferable to prospective gating. For example, cardiac imaging in multiple mice simultaneously is one such application. In this work we investigate the use of retrospective gating for cardiac imaging in a mouse. Using a three‐dimensional imaging protocol, we show that image quality with retrospective gating is comparable to prospectively gated imaging. We conclude that retrospective gating is applicable for small animal cardiac MRI and show how it can be applied to the problem of cardiac MRI in multiple mice. Magn Reson Med, 2006.

Ultrasound-guided left-ventricular catheterization: a novel method of whole mouse perfusion for microimaging

We describe a novel technique to perform whole-body perfusion fixation in mice with specific relevance to micro-imaging. With the guidance of high-frequency ultrasound imaging, we were able to perfuse fixative and contrast agents via a catheter inserted into the left ventricle, and therefore preserved the integrity of the chest and abdominal cavity. In this preliminary study, our success rate over 15 animals was 73%. We demonstrate applications of this technique for magnetic resonance imaging and micro-CT, but we expect that this method can be generally applied to whole-body perfusions of other small animals in which the intact body is necessary.

Three-dimensional, in vivo MRI with self-gating and image coregistration in the mouse.

Motion during magnetic resonance imaging (MRI) scans routinely results in undesirable image artifact or blurring. Since high‐resolution, three‐dimensional (3D) imaging of the mouse requires long scan times for satisfactory signal‐to‐noise ratio (SNR) and image quality, motion‐related artifacts are likely over much of the body and limit applications of mouse MRI. In this investigation, we explored the use of self‐gated imaging methods and image coregistration for improving image quality in the presence of motion. Self‐gated signal results from a modified 3D gradient‐echo sequence showed detection of periodic respiratory and cardiac motion in the adult mouse—with excellent comparison to traditional measurements, sensitivity to respiration‐induced tissue changes in the brain, and even detection of embryonic cardiac motion in utero. Serial image coregistration with rapidly‐acquired, low‐SNR volumes further enabled detection and correction of bulk changes in embryo location during in utero imaging sessions and subsequent reconstruction of high‐quality images. These methods, in combination, are shown to expand the range of applications for 3D mouse MRI, enabling late‐stage embryonic heart imaging and introducing the possibility of longitudinal developmental studies from embryonic stages through adulthood. Magn Reson Med, 2009.

Wanted dead or alive? The tradeoff between in-vivo versus ex-vivo MR brain imaging in the mouse

High-resolution MRI of the mouse brain is gaining prominence in estimating changes in neuroanatomy over time to understand both normal developmental as well as disease processes and mechanisms. These types of experiments, where a change in time is to be captured as accurately as possible using imaging, face multiple experimental design choices. Chief amongst these choices is whether to image ex-vivo, where superior resolution and contrast are available, or in-vivo, where resolution and contrast are lower but the animal can be followed longitudinally. Here we explore this tradeoff by first estimating the sources of variability in anatomical mouse MRI and then, using statistical simulations, provide power analyses of these experiment design choices.

Fast spin-echo for multiple mouse magnetic resonance phenotyping

High‐resolution magnetic resonance imaging is emerging as a powerful tool for phenotyping mice in biologic studies of genetic expression, development, and disease progression. In several applications, notably random mutagenesis trials, large cohorts of mice must be examined for abnormalities that may occur in any part of the body. In the aim of establishing a protocol for imaging multiple mice simultaneously in a standardized high‐throughput fashion, this study investigates variations of a three‐dimensional fast spin‐echo sequence that implements driven equilibrium, modified refocusing, and partial excitation pulses. Sequence variations are compared by simulated and experimental measurements in phantoms and mice. Results indicate that when using a short repetition time (TR ≤ T1) a sequence employing a partial excitation tip angle provides both improved signal and good T2 contrast compared with standard fast spin‐echo imaging. This sequence is used to simultaneously acquire four live mouse head images at 100 μm isotropic resolution with a scan time under 3 h at 7 T. Magn Reson Med, 2005.

In vivo MRI of neural cell migration dynamics in the mouse brain

Multipotent neuroblasts (NBs) are produced throughout life by neural stem cells in the forebrain subventricular zone (SVZ), and are able to travel long distances to the olfactory bulb. On arrival in the bulb, migrating NBs normally replace olfactory neurons, raising interest in their potential for novel cell replacement therapies in various disease conditions. An understanding of the migratory capabilities of NBs is therefore important, but as yet quantitative in vivo measurement of cell migration has not been possible. In this study, targeted intracerebral injections of iron-oxide particles to the mouse SVZ were used to label resident NBs in situ, and their migration was tracked noninvasively over time with magnetic resonance imaging (MRI). Quantitative intensity metrics were employed to identify labeled cells and to show that cells are able to travel at speeds up to 100 microm/h en route to the olfactory bulb, but that distribution through the olfactory bulb occurs at a much slower rate. In addition, comparison of histological and MRI measures of iron-oxide particle distribution were in excellent agreement. Immunohistochemistry analysis 1-3 weeks after labeling revealed that the majority of labeled cells in the olfactory bulb were immature neurons, although iron-oxide particles were also found in astrocytes and microglia. This work indicates that dynamic measurements of endogenous cell migration can be made with MRI and represents the first in vivo measurement of NB migration rates. The use of MRI in future studies tracking endogenous NB cells will permit a more complete evaluation of their role during homeostasis at various developmental stages and during disease progression.

Mouse behavioral mutants have neuroimaging abnormalities.

Impaired cognitive, memory, or motor performance is a distinguishing characteristic of neurological diseases. Although these symptoms are frequently the most evident in human patients, additional markers of disease are critical for proper diagnosis and staging. Noninvasive neuroimaging methods have become essential in this capacity and provide means of evaluating disease and tracking progression. These imaging methods are also becoming available to scientists in the research laboratory for assessment of animal models of neurological disease. Imaging in mouse models of neurological disease is of particular interest, owing to the availability of inbred strains and genetic manipulation tools that permit detailed investigation of the roles of various genes and gene products in disease pathogenesis. However, the relative prevalence of neuroimaging abnormalities in mice exhibiting neurological symptoms has not been reported. This prevalence has both theoretical and practical value because it is influenced by both the sensitivity of macroscopic anatomical measures to underlying genetic and disease processes and by the efficiency of neuroimaging in detecting and characterizing these effects. In this paper, we describe a meta‐analysis of studies involving behavioral mouse mutants at our laboratory. In summary, we have evaluated 15 different mutant genotypes, of which 13 showed abnormal neuroimaging findings. This indicates a surprisingly high prevalence of neuroimaging abnormalities (87%) and suggests that disease processes affecting behavior generally alter neuroanatomy as well. As a consequence, neuroimaging provides a highly sensitive marker of neurological disease in mice exhibiting abnormal behavior. Hum Brain Mapp 2007.