Post-meiotic mechanism of facultative parthenogenesis in gonochoristic whiptail lizard species.

Facultative parthenogenesis (FP) has historically been regarded as rare in vertebrates, but in recent years incidences have been reported in a growing list of fish, reptile, and bird species. Despite the increasing interest in the phenomenon, the underlying mechanism and evolutionary implications have remained unclear. A common finding across many incidences of FP is either a high degree of homozygosity at microsatellite loci or low levels of heterozygosity detected in next-generation sequencing data.

Gamete Collection and In Vitro Fertilization of Astyanax mexicanus.

Astyanax mexicanus is emerging as a model organism for a variety of research fields in biological science. Part of the recent success of this teleost fish species is that it possesses interfertile cave and river-dwelling populations. This enables the genetic mapping of heritable traits that were fixed during adaptation to the different environments of these populations.

Widespread failure to complete meiosis does not impair fecundity in parthenogenetic whiptail lizards.

Parthenogenetic species of whiptail lizards in the genus Aspidoscelis constitute a striking example of speciation by hybridization, in which first-generation hybrids instantly attain reproductive isolation and procreate as clonal all-female lineages. Production of eggs containing a full complement of chromosomes in the absence of fertilization involves genome duplication prior to the meiotic divisions. In these pseudo-tetraploid oocytes, pairing and recombination occur exclusively between identical chromosomes instead of homologs; a deviation from the normal meiotic program that maintains heterozygosity.

The Veiled Chameleon (Chamaeleo calyptratus Duméril and Duméril 1851): A Model for Studying Reptile Body Plan Development and Evolution.

Vertebrate model organisms have facilitated the discovery and exploration of morphogenetic events and developmental pathways that underpin normal and pathological embryological events. In contrast to amniotes such as Mus musculus (Mammalia) and Gallus gallus (Aves), our understanding of early patterning and developmental events in reptiles (particularly nonavians) remains weak. Squamate reptiles (lizards, snakes, and amphisbaenians) comprise approximately one-third of all living amniotes.

Captive Care, Raising, and Breeding of the Veiled Chameleon (Chamaeleo calyptratus).

Squamate reptiles comprise approximately one-third of all living amniotes. In most of these species, it is difficult to study gastrulation and neurulation because the embryos are at a late stage of development at the time of oviposition. This is not the case, however, in veiled chameleons (Chamaeleo calyptratus), which are increasingly being used as a model organism to study these and other developmental and evolutionary phenomena.

The effect of stocking densities on reproductive performance in laboratory zebrafish (Danio rerio).

Despite the growing popularity of the zebrafish model system, the optimal husbandry conditions for this animal are not well defined. The aim of this study was to examine the effect of stocking density on reproductive performance in zebrafish. In this study, undertaken by eight different zebrafish facilities, clutches of at least 200 wild-type zebrafish embryos from a single pairwise mating were produced at each participating institution and subsequently reared according to "in-house protocols" until they were 14 weeks old.

Laboratory synthesis of an independently reproducing vertebrate species.

Speciation in animals commonly involves an extrinsic barrier to genetic exchange followed by the accumulation of sufficient genetic variation to impede subsequent productive interbreeding. All-female species of whiptail lizards, which originated by interspecific hybridization between sexual progenitors, are an exception to this rule. Here, the arising species instantaneously acquires a novel genotype combining distinctive alleles from two different species, and reproduction by parthenogenesis constitutes an effective intrinsic barrier to genetic exchange.

Sister chromosome pairing maintains heterozygosity in parthenogenetic lizards.

Although bisexual reproduction has proven to be highly successful, parthenogenetic all-female populations occur frequently in certain taxa, including the whiptail lizards of the genus Aspidoscelis. Allozyme analysis revealed a high degree of fixed heterozygosity in these parthenogenetic species, supporting the view that they originated from hybridization events between related sexual species. It has remained unclear how the meiotic program is altered to produce diploid eggs while maintaining heterozygosity.

Regulatory compliance and the zebrafish.

The growth of the zebrafish as a model organism has so far greatly outpaced regulatory oversight governing its care and use in research. However, the same levels of regulation that characterize the use of traditional mammalian model animals will likely be extended to zebrafish, especially as use of the animal continues to increase. The challenge for both the zebrafish research community and regulatory agents is to ensure that emerging guidelines are sensible and serve to promote quality science and the highest standards of animal care.

A family of GFP-like proteins with different spectral properties in lancelet Branchiostoma floridae.

Background: Members of the green fluorescent protein (GFP) family share sequence similarity and the 11-stranded beta-barrel fold. Fluorescence or bright coloration, observed in many members of this family, is enabled by the intrinsic properties of the polypeptide chain itself, without the requirement for cofactors. Amino acid sequence of fluorescent proteins can be altered by genetic engineering to produce variants with different spectral properties, suitable for direct visualization of molecular and cellular processes.

Control of segment number in vertebrate embryos.

The vertebrate body axis is subdivided into repeated segments, best exemplified by the vertebrae that derive from embryonic somites. The number of somites is precisely defined for any given species but varies widely from one species to another. To determine the mechanism controlling somite number, we have compared somitogenesis in zebrafish, chicken, mouse and corn snake embryos.

PTK787/ZK222584, a tyrosine kinase inhibitor of vascular endothelial growth factor receptor, reduces uptake of the contrast agent GdDOTA by murine orthotopic B16/BL6 melanoma tumours and inhibits their growth in vivo.

Assessment of tumour vascularity may characterize malignancy as well as predict responsiveness to anti-angiogenic therapy. Non-invasive measurement of tumour perfusion and blood vessel permeability assessed as the transfer constant, K(trans), can be provided by dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI). Using the orthotopic murine tumour model B16/BL6 melanoma, the small contrast agent GdDOTA (DOTAREM(R); Guerbet, Paris) was applied to assess the vascular transfer constant, K(trans), and interstitial leakage space, whereas intravascular iron oxide nanoparticles (Endorem(R); Guerbet, Paris) were used to detect relative tumour blood volume (rTBV), and in one experiment blood flow index (BFI).

The pharmacological stimulation of NMDA receptors via co-agonist site: an fMRI study in the rat brain.

d-Serine has been proposed as an endogenous modulator at the co-agonist glycine-binding site of N-methyl-d-aspartate (NMDA) receptors. There is still some debate as to whether this site is saturated in vivo, but it seems likely that this depends on regional differences in local glycine or d-serine concentrations. In order to identify areas where the co-agonist site was not fully activated in vivo, we studied the effect of intraperitoneal d-serine administration in the rat brain using functional magnetic resonance imaging (fMRI).

Predictability of FTY720 efficacy in experimental autoimmune encephalomyelitis by in vivo macrophage tracking: clinical implications for ultrasmall superparamagnetic iron oxide-enhanced magnetic resonance imaging.

Purpose: To examine the efficacy of FTY720 as a new agent to reduce inflammatory activity in an animal model of multiple sclerosis (MS) by in vivo macrophage tracking.

Material And Methods: FTY720 was used for treatment of rats in a model of chronic relapsing experimental autoimmune encephalomyelitis (EAE) at an oral dose of 0.3 mg/kg/day.

Age-dependent impairment of somatosensory response in the amyloid precursor protein 23 transgenic mouse model of Alzheimer's disease.

Quantitative functional magnetic resonance imaging was applied to characterize brain function in amyloid precursor protein 23 (APP23) transgenic mice, which reproduce the neuropathological alterations associated with Alzheimer's disease. Electrical stimulation of the paw led to cerebral blood volume increases in the contralateral somatosensory cortex. In APP23 mice this hemodynamic response decreased with increasing age of the animal and with increasing stimulus amplitude as compared with wild-type animals.

Characterization of CNS disorders and evaluation of therapy using structural and functional MRI.

Modern drug development requires technologies that allow rapid translation from the preclinical to the clinical stage. It is obvious that non-invasive imaging modalities such as magnetic resonance imaging (MRI) will play a central role in this regard. This article reviews the use of structural and functional MRI readouts for characterization of central nervous system (CNS) disorders and evaluation of the efficacy of potential CNS drugs.

Impaired functionality of reperfused brain tissue following short transient focal ischemia in rats.

Functional magnetic resonance imaging (fMRI) has been applied to study the consequences of transient focal ischemia on neuronal excitability in the rat brain. The experimental paradigm consisted of measuring the changes in local cerebral blood volume (CBV) induced by systemic infusion of the GABA(A) antagonist bicuculline after occlusion of the middle cerebral artery (MCA) for durations of 5, 15, 30 and 60 min using the intraluminal thread model. fMRI studies were carried out 60 min after successful reperfusion of the ischemic territory.

Compromised hemodynamic response in amyloid precursor protein transgenic mice.

APP23 transgenic mice overexpressing amyloid precursor protein (APP751) reproduce neuropathological changes associated with Alzheimer's disease such as high levels of amyloid plaques, cerebral amyloid angiopathy, and associated vascular pathologies. Functional magnetic resonance imaging (fMRI) was applied to characterize brain functionality in these mice through global pharmacological stimulation. The cerebral hemodynamic response to infusion of the GABA(A) antagonist bicuculline was significantly reduced in aged APP23 mice compared with age-matched wild-type littermates.

Recovery of function in cytoprotected cerebral cortex in rat stroke model assessed by functional MRI.

Functional recovery in cytoprotected somatosensory cortex in a rat stroke model was studied using functional MRI (fMRI). Calcium antagonist treatment (isradipine) following permanent middle cerebral artery occlusion (pMCAO) reduced the infarct volume by 33 +/- 9%. The somatosensory cortex representing the forepaws was spared from infarction; however, cerebral blood flow (CBF) was significantly reduced in this area 24 hr following pMCAO.