Down's syndrome-like cardiac developmental defects in embryos of the transchromosomic Tc1 mouse

Aims Cardiac malformations are prevalent in trisomies of human chromosome 21 [Down's syndrome (DS)], affecting normal chamber separation in the developing heart. Efforts to understand the aetiology of these defects have been severely hampered by the absence of an accurate mouse model. Such models have proved challenging to establish because synteny with human chromosome Hsa21 is distributed across three mouse chromosomes. None of those engineered so far accurately models the full range of DS cardiac phenotypes, in particular the profound disruptions resulting from atrioventricular septal defects (AVSDs). Here, we present analysis of the cardiac malformations exhibited by embryos of the transchromosomic mouse line Tc(Hsa21)1TybEmcf (Tc1) which contains more than 90% of chromosome Hsa21 in addition to the normal diploid mouse genome. Methods and results Using high-resolution episcopic microscopy and three-dimensional (3D) modelling, we show that Tc1 embryos exhibit many of the cardiac defects found in DS, including balanced AVSD with single and separate valvar orifices, membranous and muscular ventricular septal defects along with outflow tract and valve leaflet abnormalities. Frequencies of cardiac malformations (ranging from 38 to 55%) are dependent on strain background. In contrast, no comparable cardiac defects were detected in embryos of the more limited mouse trisomy model, Dp(16Cbr1-ORF9)1Rhr (Ts1Rhr), indicating that trisomy of the region syntenic to the Down's syndrome critical region, including the candidate genes DSCAM and DYRK1A, is insufficient to yield DS cardiac abnormalities. Conclusion The Tc1 mouse line provides a suitable model for studying the underlying genetic causes of the DS AVSD cardiac phenotype

Population genetic structure associated with a landscape barrier in the Western Grasswren (Amytornis textilis textilis)

Dispersal patterns can dictate genetic population structure and, ultimately, population resilience, through maintaining gene flow and genetic diversity. However, geographical landforms, such as peninsulas, can impact dispersal patterns and thus be a barrier to gene flow. Here, we use 13 375 genome-wide single-nucleotide polymorphisms (SNPs) to evaluate genetic population structure and infer dispersal patterns of the Western Grasswren Amytornis textilis textilis (WGW, n = 140) in the Shark Bay region of Western Australia. We found high levels of genetic divergence between subpopulations on the mainland (Hamelin) and narrow peninsula (Peron). In addition, we found evidence of further genetic sub-structuring within the Hamelin subpopulation, with individuals collected from the western and eastern regions of a conservation reserve forming separate genetic clusters. Spatial autocorrelation analysis within each subpopulation revealed significant local-scale genetic structure up to 35 km at Hamelin and 20 km at Peron. In addition, there was evidence of male philopatry in both subpopulations. Our results suggest a narrow strip of land may be acting as a geographical barrier in the WGW, limiting dispersal between a peninsula and mainland subpopulation. In addition, heterogeneous habitat within Hamelin may be restricting dispersal at the local scale. Furthermore, there is evidence to suggest that the limited gene flow is asymmetrical, with directional dispersal occurring from the bounded peninsula subpopulation to the mainland. This study highlights the genetic structure existing within and between some of the few remaining WGW subpopulations, and shows a need to place equal importance on conservation efforts to maintain them in the future

Comprehensive phenotypic analysis of the Dp1Tyb mouse strain reveals a broad range of Down syndrome-related phenotypes

Down syndrome (DS), trisomy 21, results in many complex phenotypes including cognitive deficits, heart defects and craniofacial alterations. Phenotypes arise from an extra copy of human chromosome 21 (Hsa21) genes. However, these dosage-sensitive causative genes remain unknown. Animal models enable identification of genes and pathological mechanisms. The Dp1Tyb mouse model of DS has an extra copy of 63% of Hsa21-orthologous mouse genes. In order to establish whether this model recapitulates DS phenotypes, we comprehensively phenotyped Dp1Tyb mice using 28 tests of different physiological systems and found that 468 out of 1800 parameters were significantly altered. We show that Dp1Tyb mice have wide-ranging DS-like phenotypes, including aberrant erythropoiesis and megakaryopoiesis, reduced bone density, craniofacial changes, altered cardiac function, a pre-diabetic state, and deficits in memory, locomotion, hearing and sleep. Thus, Dp1Tyb mice are an excellent model for investigating complex DS phenotype-genotype relationships for this common disorder

Patterns of morphological and mitochondrial diversity in parapatric subspecies of the Thick-billed Grasswren (<i>Amytornis modestus</i>)

<p>Divergence is the first phase of speciation and is commonly thought to occur more readily in allopatric populations. Subspecies are populations that are divergent but generally retain the capacity to interbreed should they come into contact. Two subspecies of the Thick-billed Grasswren (<i>Amytornis modestus</i>) are divergent by 1.7% at the mitochondrial ND2 gene and were previously considered to be allopatric. In this study, we discovered that the subspecies were parapatric. We use a larger sample size than previous studies to examine variation in morphology and mitochondrial haplotype across the distribution of each subspecies and within the region of parapatry. The subspecies occurring to the west, <i>Amytornis modestus indulkanna</i>, had larger body size and longer and narrower bill than the subspecies occurring to the east, <i>A. m. raglessi</i>. Within the region of parapatry, females were morphologically similar to <i>A. m. indulkanna</i> but had eastern mitochondrial haplotypes while males had intermediate morphology and either eastern or western haplotypes. Additionally, haplotypes from the western mitochondrial clade were found in <i>A. m. raglessi</i>. These patterns of morphology and mitochondrial diversity reveal discordance within the region of parapatry and to the east. We suggest that the subspecies have undergone asymmetric expansion from west to east, made secondary contact, and are currently hybridising.</p

Thick-billed grasswren (<i>Amytornis modestus</i>) songs differ across subspecies and elicit different subspecific behavioural responses

<p>Passerine song has many functions including mate attraction and territory defence. When songs across populations diverge, this can lead to changes in conspecific recognition and barriers to gene flow, which affect evolutionary processes that could lead to speciation. Two subspecies of thick-billed grasswren (<i>Amytornis modestus</i>) have a parapatric distribution characterised as a narrow region of high genetic admixture where the two subspecies meet. Outside the region of parapatry, the subspecies are genetically and morphologically diverged and weak inter-subspecific gene flow is asymmetric from <i>A. m. indulkanna</i> to <i>A. m. raglessi</i>. We examined the differences between song of <i>A. m. indulkanna</i> and <i>A. m. raglessi</i> and experimentally broadcast each subspecies song to compare territory-holder response in relation to intruder subspecies type. Our aim was to determine if territory owners have a different response to intruders based on the subspecific song type. The song of each subspecies contained unique vocal elements that were absent in the other subspecies. <i>A. m. raglessi</i> responded similarly to con-subspecific and hetero-subspecific intruder song, and <i>A. m. indulkanna</i> responded more often and with greater intensity to hetero- compared to con-subspecific intruder song. The stronger response by <i>A. m. indulkanna</i> towards hetero-subspecific intruders provides a plausible behavioural explanation for the observed patterns of asymmetrical gene flow.</p

Increased Allergic Immune Response to Sarcoptes scabiei Antigens in Crusted versus Ordinary Scabies▿

Scabies, a parasitic skin infestation by the burrowing “itch” mite Sarcoptes scabiei, causes significant health problems for children and adults worldwide. Crusted scabies is a particularly severe form of scabies in which mites multiply into the millions, causing extensive skin crusting. The symptoms and signs of scabies suggest host immunity to the scabies mite, but the specific resistant response in humans remains largely uncharacterized. We used 4 scabies mite recombinant proteins with sequence homology to extensively studied house dust mite allergens to investigate a differential immune response between ordinary scabies and the debilitating crusted form of the disease. Subjects with either disease form showed serum IgE against recombinant S. scabiei cysteine and serine proteases and apolipoprotein, whereas naive subjects showed minimal IgE reactivity. Significantly (P < 0.05) greater serum IgE and IgG4 binding to mite apolipoprotein occurred in subjects with crusted scabies than in those with ordinary scabies. Both subject groups showed strong proliferative responses (peripheral blood mononuclear cells) to the scabies antigens, but the crusted scabies group showed increased secretion of the Th2 cytokines interleukin 5 (IL-5) and IL-13 and decreased Th1 cytokine gamma interferon (IFN-γ) in response to the active cysteine protease. These data confirm that a nonprotective allergic response occurs in the crusted disease form and demonstrate that clinical severity is associated with differences in the type and magnitude of the antibody and cellular responses to scabies proteins. A quantitative IgE inhibition assay identified IgE immunoreactivity of scabies mite antigens distinct from that of house dust mite antigens, which is potentially important for specific scabies diagnosis and therapy

Dendritic spine classification by morphology, in Tc1 and Ts1Rhr mouse cortex.

<p><b><i>A</i></b>. At P21, there were significantly fewer thin spines in Ts1Rhr cortex at P21 (Ts1Rhr 24.30%±1.38, wildtype 32.77%±2.27; p<0.05; n = ≥19 neurons from ≥5 animals per genotype) <b><i>B</i></b>. Dendritic spine classifications in 3-month-old mouse cortex shows significantly fewer mushroom spines (Tc1 26.25%±1.92, wildtype 33.86%±1.62; p<0.05; n = ≥15 neurons from ≥3 animals per genotype) but significantly more stubby spines in Tc1 cortex, compared with wildtype controls (Tc1 52.86%±3.07, wildtype 45.29%±1.74; p<0.05). *p<0.05.</p

Hsa21, orthologous mouse chromosome regions and relevant DS mouse models.

<p>The proposed Down Syndrome Critical Region (DSCR), a region of approximately 33 genes formerly thought to be sufficient to produce DS phenotypes, is located on the long arm of Hsa21. Hsa21 is syntenic with regions of mouse chromosomes 16, 17 and 10. The Tc1 mouse carries a freely segregating copy of Hsa21, but suffers from regions of deletion (the two largest are shown) and duplication. The asterisk represents the deleted region where genes involved in synaptic development (<i>ITSN, SYNJ</i> and <i>DSCR1</i>) are located. Ts65Dn is a duplication of approximately 140 Mmu16 genes. Ts1Rhr is a duplication of the Mmu16 region corresponding to the DSCR.</p