The mammalian cervical vertebrae blueprint depends on the T (brachyury) gene

Mitochondrial genes modulate the phenotypic expression of congenital scoliosis syndrome caused by mutations in the TBXT gene

BACKGROUND

Congenital scoliosis (CS) is a spinal disorder caused by genetic-congenital vertebral malformations and may be associated with other congenital defects or may occur alone. It is genetically heterogeneous and numerous genes contributing to this disease have been identified. In addition, CS has a wide range of phenotypic and genotypic variability, which has been explained by the intervention of genetic factors like modifiers and environment genes. The aim of the present study was to determine the possible cause of CS in a Tunisian patient and to examine the association between mtDNA mutations and mtDNA content and CS.

METHODS

Here we performed Whole-Exome Sequencing (WES) in a patient presenting clinical features suggestive of severe congenital scoliosis syndrome. Direct sequencing of the whole mitochondrial DNA (mtDNA) was also performed in addition to copy number quantification in the blood of the indexed case. In silico prediction tools, 3D modeling and molecular docking approaches were used.

RESULTS

The WES revealed the homozygous missense mutation c.512A > G (p.H171R) in the TBXT gene. Bioinformatic analysis demonstrated that the p.H171R variant was highly deleterious and caused the TBXT structure instability. Molecular docking revealed that the p.H171R mutation disrupted the monomer stability which seemed to be crucial for maintaining the stability of the homodimer and consequently to the destabilization of the homodimer-DNA complex. On the other hand, we hypothesized that mtDNA can be a modifier factor, so, the screening of the whole mtDNA showed a novel heteroplasmic m.10150T > A (p.M31K) variation in the MT-ND3 gene. Further, qPCR analyses of the patient's blood excluded mtDNA depletion. Bioinformatic investigation revealed that the p.M31K mutation in the ND3 protein was highly deleterious and may cause the ND3 protein structure destabilization and could disturb the interaction between complex I subunits.

CONCLUSION

We described the possible role of mtDNA genetics on the pathogenesis of congenital scoliosis by hypothesizing that the presence of the homozygous variant in TBXT accounts for the CS phenotype in our patient and the MT-ND3 gene may act as a modifier gene.

Generation of sheep with defined FecBB and TBXT mutations and porcine blastocysts with KCNJ5G151R/+ mutation using prime editing

BACKGROUND

Rewriting the genomes of living organisms has been a long-standing aim in the biological sciences. The revelation of the CRISPR/Cas9 technology has revolutionized the entire biological field. Since its emergence, this technology has been widely applied to induce gene knockouts, insertions, deletions, and base substitutions. However, the classical version of this system was imperfect for inducing or correcting desired mutations. A subsequent development generated more advanced classes, including cytosine and adenine base editors, which can be used to achieve single nucleotide substitutions. Nevertheless, these advanced systems still suffer from several limitations, such as the inability to edit loci without a suitable PAM sequence and to induce base transversions. On the other hand, the recently emerged prime editors (PEs) can achieve all possible single nucleotide substitutions as well as targeted insertions and deletions, which show promising potential to alter and correct the genomes of various organisms. Of note, the application of PE to edit livestock genomes has not been reported yet.

RESULTS

In this study, using PE, we successfully generated sheep with two agriculturally significant mutations, including the fecundity-related FecB^B p.Q249R and the tail length-related TBXT p.G112W. Additionally, we applied PE to generate porcine blastocysts with a biomedically relevant point mutation (KCNJ5 p.G151R) as a porcine model of human primary aldosteronism.

CONCLUSIONS

Our study demonstrates the potential of the PE system to edit the genomes of large animals for the induction of economically desired mutations and for modeling human diseases. Although prime-edited sheep and porcine blastocysts could be generated, the editing frequencies are still unsatisfactory, highlighting the need for optimizations in the PE system for efficient generation of large animals with customized traits.

Frequency and Characterisation of Anomalies and Fractures of the Caudal Spine in Sheep with Undocked Tails

As tails are often docked within the first days of life, studies investigating tail malformations and injuries in sheep do not exist thus far. To address this gap in the literature, this research aimed to analyse the occurrence of vertebral anomalies and fractures in the tail within an undocked Merinoland sheep population. At 14 weeks of age, the caudal spines of 216 undocked Merinoland lambs was radiographically examined, and tail length and circumference were measured. Anomalies were documented and statistical correlation and model calculations were performed. The occurrence of block vertebrae was observed in 12.96% and wedged vertebrae in 8.33% of the sample. Of the animals, 59 (27.31%) exhibited at least one vertebral fracture, which were observed in the middle and caudal third of the tail. A significant correlation was found between the occurrence of fractures and tail length (r = 0.168) and number of vertebrae (r = 0.155). Conversely, the presence of block and wedged vertebrae was not significantly correlated with tail length, circumference, or number of vertebrae. Only the sex showed significant differences in the probability of axis deviation. These results emphasize the importance of breeding for short tails to avoid fractures.

[Phenotyping the sheep tail - Presentation of characterization methods in the context of breeding for short-tailedness]

OBJECTIVE

In order to establish targeted breeding for short-tailedness, a suitable method must initially be found that allows phenotyping of the sheep tail beyond tail length. In this study, in addition to assessing body measurements, more advanced studies such as ultrasonography and radiology were performed on the caudal spine of sheep for the first time. The objective of this work was to analyze the physiological variation of tail lengths and vertebrae within a merino sheep population. It also aimed to validate the use of sonographic gray scale analysis and perfusion measurement on the sheep tail.

MATERIAL AND METHOD

Tail length and circumference in centimeters were measured in 256 Merino lambs on the first or second day of life. At 14 weeks of age the caudal spine of these animals was examined radiographically. Sonographic gray scale analysis and measurement of the perfusion velocity of the caudal artery mediana were also performed in a portion of the animals.

RESULTS

The tested method of measurement showed a standard error of 0,08 cm and a coefficient of variation of 0,23% for tail length and 0,78% for tail circumference. The animals had a mean tail length of 22,5±2,32 cm and a mean tail circumference of 6,53±0,49 cm. The mean caudal vertebrae count for this population was 20,4±1,6. The use of a mobile radiographic unit is well suited for imaging the caudal spine in sheep. It was demonstrated that the caudal median artery could be imaged for measurement of perfusion velocity (cm/s), and sonographic gray-scale analysis also showed good feasibility. The mean gray scale value is 19,74±4,5 and the modal value for the most commonly found gray scale pixels is 191,53±120,2. The mean perfusion velocity for the caudal artery mediana is 5,83±3,04 cm/s.

CONCLUSION

The results show that the methods presented are well suited for further characterization of the ovine tail. For the first time, gray values for the tail tissue and the perfusion velocity of the caudal artery mediana were determined.

Bedeutung der Schwanzlänge beim Schaf und Zucht auf Kurzschwänzigkeit

Eine Möglichkeit, das Kopieren von Schwänzen bei Schafen in der Zukunft zu vermeiden, stellt die Zucht auf Kurzschwänzigkeit dar. Dies erscheint vielversprechend, da die Urform der Hausschafe, der Mufflon, einen relativ kurzen schmalen Schwanz besitzt. Es kann folglich davon ausgegangen werden, dass längere Schwänze ein Resultat der Domestikation sind. Ältere Untersuchungen zur Heritabilität der Schwanzlänge beim Hausschaf konnten rasseabhängig Werte von 0,38 bis 0,77 nachweisen. Bei der Zucht auf Kurzschwänzigkeit muss jedoch darauf geachtet werden, dass keine Missbildungen der Wirbelsäule und benachbarter Strukturen auftreten. Bis in diesem Bereich ein Zuchtfortschritt erreicht ist, können durch Managementmaßnahmen die negativen Auswirkungen länger bewollter Schwänze (z. B. Myiasisbefall, Dermatitis) gemindert werden. Dazu gehören die Vermeidung von Durchfällen durch eine ausgewogene wiederkäuergerechte Fütterung, ein betriebsspezifisch angepasstes nachhaltiges Parasitenmanagementprogramm und die gezielte Schur unkupierter Schwänze.

Congenital syringohydromyelia in a crossbred (Holstein-Friesian × Japanese Black) beef calf

A 5-day-old male crossbred beef calf presented with a well-coordinated bilateral hopping gait of the hind limbs. Postmortem CT showed a poorly defined oval-shaped region at the L3–L4 spinal segments, which had high signal intensity on T2 weighted postmortem MRI images. On pathological examination, we identified a large cystic cavity filled with a large amount of cerebrospinal fluid on the cut surface of the spinal region. Histopathological examination revealed that the spinal cord parenchyma was compressed by the cystic structure, and the cystic cavity was lined with a thin layer of discrete ependymal cells, indicating syringohydromyelia. This is the first reported case of a Holstein-Friesian × Japanese Black crossbred calf with solitary syringohydromyelia. Our findings suggest that myelodysplasia with cystic cavities can be suspected by CT, without the need for MRI.

Genetic variants of TBX6 and TBXT identified in patients with congenital scoliosis in Southern China

Congenital scoliosis (CS) is a spinal deformity present at birth due to underlying congenital vertebral malformation (CVM) that occurs during embryonic development. Hemivertebrae is the most common anomaly that causes CS. Recently, compound heterozygosity in TBX6 has been identified in Northern Chinese, Japanese, and European CS patient cohorts, which explains about 7%-10% of the affected population. In this report, we recruited 67 CS patients characterized with hemivertebrae in the Southern Chinese population and investigated the TBX6 variant and risk haplotype. We found that two patients with hemivertebrae in the thoracic spine and one patient with hemivertebrae in the lumbar spine carry the previously defined pathogenic TBX6 compound heterozygous variants. In addition, whole exome sequencing of patients with CS and their family members identified a de novo missense mutation (c.G47T: p.R16L) in another member of the T-box family, TBXT. This rare mutation compromised the binding of TBXT to its target sequence, leading to reduced transcriptional activity, and exhibited dominant-negative effect on wild-type TBXT. Our findings further highlight the importance of T-box family genes in the development of congenital scoliosis.

Maternal and direct genetic parameters for tail length, tail lesions, and growth traits in pigs

Tail length and tail lesions are the major triggers for tail biting in pigs. Against this background, 2 datasets were analyzed to estimate genetic parameters for tail characteristics and growth traits. Dataset 1 considered measurements for trait tail length (T-LEN) and for the growth traits birth weight (BW), weaning weight (WW), postweaning weight (PWW), and average daily gain (ADG) from 9,348 piglets. Piglets were born in the period from 2015 to 2018 and kept on the university Gießen research station. Dataset 2 included 4,943 binary observations from 1,648 pigs from the birth years 2016 to 2019 for tail lesions (T-LES) as indicators for nail necrosis, tail abnormalities, or tail biting. T-LES were recorded at 30 ± 7 d after entry for rearing (T-Les-1), at 50 ± 7 d after entry for rearing (end of the rearing period, T-LES-2), and 130 ± 20 d after entry for rearing (end of fattening period, T-LES-3). Genetic statistical model evaluation for dataset 1 based on Akaike's information criterion and likelihood ration tests suggested multiple-trait animal models considering covariances between direct and maternal genetic effects. The direct heritability for T-LEN was 0.42 (±0.03), indicating the potential for genetic selection on short tails. The maternal genetic heritability for T-LEN was 0.05 (±0.04), indicating the influence of uterine characteristics on morphological traits. The negative correlation between direct and maternal effects for T-LEN of -0.35 (±0.13), as well as the antagonistic relationships (i.e., positive direct genetic correlations in the range from 0.03 to 0.40) between T-LEN with the growth traits BW, WW, PWW, and ADG, complicate selection strategies and breeding goal definitions. The correlations between direct effects for T-LEN and maternal effects for breeding goal traits, and vice versa, were positive but associated with a quite large SE. The heritability for T-LES when considering the 3 repeated measurements was 0.23 (±0.04) from the linear (repeatability of 0.30) and 0.21 (±0.06; repeatability of 0.29) from the threshold model. The breeding value correlations between T-LES-3 with breeding values from the repeatability models were quite large (0.74 to 0.90), suggesting trait lesion recording at the end of the rearing period. To understand all genetic mechanisms in detail, ongoing studies are focusing on association analyses between T-LEN and T-LES, and the identification of tail biting from an actor's perspective.

Two linked TBXT (brachyury) gene polymorphisms are associated with the tailless phenotype in fat-rumped sheep

T‐box transcription factor T (TBXT), encoding the brachyury protein, is an embryonic nuclear transcription factor involved in mesoderm formation and differentiation. Previous studies indicate that TBXT mutations are responsible for the tailless or short‐tailed phenotype of many vertebrates. To verify whether the tailless phenotype in fat‐rumped sheep is associated with TBXT mutations, exon 2 of the TBXT gene for 301 individuals belonging to 13 Chinese and Iranian sheep breeds was directly sequenced. Meanwhile, 380 samples were used to detect the genotypes of the candidate variations by mapping to their reads databases in the Sequence Read Archive repository of GenBank. The results showed that one missense mutation, c.334G>T (GGG>TGG) with a completely linked synonymous variant c.333G>C (CCG>CCC) was found to be associated with the ‘tailless’ characteristic in typical fat‐rumped sheep breeds. The c.334G>T transversion led to the conversion of glycine to tryptophan at the 112th amino acid in the T‐box domain of the brachyury protein. In addition, crossbreeding experiments for long‐tailed and tailless sheep showed that CT/CT allele of nucleotides (nt) 333 and 334, a recessive mutation, would cause sheep tails to be shorter, suggesting that these two linked variants at nucleotides 333 and 334 in TBXT are probably causative mutations responsible for the tailless phenotype in sheep.

C7 vertebra homeotic transformation in domestic dogs - are Pug dogs breaking mammalian evolutionary constraints?

The number of cervical vertebrae in mammals is almost constant at seven, regardless of their neck length, implying that there is selection against variation in this number. Homebox (Hox) genes are involved in this evolutionary mammalian conservation, and homeotic transformation of cervical into thoracic vertebrae (cervical ribs) is a common phenotypic abnormality when Hox gene expression is altered. This relatively benign phenotypic change can be associated with fatal traits in humans. Mutations in genes upstream of Hox, inbreeding and stressors during organogenesis can also cause cervical ribs. The aim of this study was to describe the prevalence of cervical ribs in a large group of domestic dogs of different breeds, and explore a possible relation with other congenital vertebral malformations (CVMs) in the breed with the highest prevalence of cervical ribs. By phenotyping we hoped to give clues as to the underlying genetic causes. Twenty computed tomography studies from at least two breeds belonging to each of the nine groups recognized by the Federation Cynologique Internationale, including all the brachycephalic 'screw-tailed' breeds that are known to be overrepresented for CVMs, were reviewed. The Pug dog was more affected by cervical ribs than any other breed (46%; P < 0.001), and was selected for further analysis. No association was found between the presence of cervical ribs and vertebral body formation defect, bifid spinous process, caudal articular process hypoplasia/aplasia and an abnormal sacrum, which may infer they have a different aetiopathogenesis. However, Pug dogs with cervical ribs were more likely to have a transitional thoraco-lumbar vertebra (P = 0.041) and a pre-sacral vertebral count of 26 (P < 0.001). Higher C7/T1 dorsal spinous processes ratios were associated with the presence of cervical ribs (P < 0.001), supporting this is a true homeotic transformation. Relaxation of the stabilizing selection has likely occurred, and the Pug dog appears to be a good naturally occurring model to further investigate the aetiology of cervical ribs, other congenital vertebral anomalies and numerical alterations.

Vertebral and spinal dysplasia: A novel dominantly inherited congenital defect in Holstein cattle

Monitoring and surveillance strategies are imperative for managing genetic defects in livestock populations in order to avoid detrimental effects on animal welfare and productivity. Recently, a number of previously unknown defects have been described in cattle, fostered by the huge progress in genome analysis and genomic selection. In response to reports about a potentially new defect in Holstein cattle, case-control studies were carried out to confirm a genetic background of the defect and to evaluate its phenotypic relevance. Eighty-five potentially affected offspring of a suspected carrier sire for the defect and 41 matched control calves were subjected to clinical and epidemiological monitoring on 39 farms. Forty-one animals, all offspring of the suspected carrier sire, showed pathognomonic tail malformations providing highly significant evidence for a congenital inherited defect, which was subsequently termed vertebral and spinal dysplasia (VSD). The defect is characterised by vertebral (specifically tail) deformities and neurological dysfunctions with gait abnormalities of the hind limbs. The deformities and neurological dysfunctions varied from very mild (only tail deformities) to severe (paraparesis). Detailed epidemiological monitoring provided no indication of environmental factors affecting VSD. The malformations and dysfunctions associated with VSD, as well as its mode of inheritance and the genotyping of the suspected carrier sire, indicated that VSD is a defect previously not described in cattle. VSD is inherited in a dominant mode, but shows incomplete penetrance of the phenotype, which impedes unequivocal identification of VSD carriers. A direct diagnostic genetic test for VSD is available.