Identification of the genomic mutation in Epha4(rb-2J/rb-2J) mice.

The EphA4 receptor tyrosine kinase is involved in numerous cell-signalling activities during embryonic development. EphA4 has the ability to bind to both types of ephrin ligands, the ephrinAs and ephrinBs. The C57BL/6J-Epha4rb-2J/GrsrJ strain, denoted Epha4(rb-2J/rb-2J), is a spontaneous mouse mutant that arose at The Jackson Laboratory. These mutants exhibited a synchronous hind limb locomotion defect or "hopping gait" phenotype, which is also characteristic of EphA4 null mice. Genetic complementation experiments suggested that Epha4(rb-2J) corresponds to an allele of EphA4, but details of the genomic defect in this mouse mutant are currently unavailable. We found a single base-pair deletion in exon 9 resulting in a frame shift mutation that subsequently resulted in a premature stop codon. Analysis of the predicted structure of the truncated protein suggests that both the kinase and sterile α motif (SAM) domains are absent. Definitive determination of genotype is needed for experimental studies of mice carrying the Epha4(rb-2J) allele, and we have also developed a method to ease detection of the mutation through RFLP. Eph-ephrin family members are reportedly expressed as numerous isoforms. Hence, delineation of the specific mutation in EphA4 in this strain is important for further functional studies, such as protein-protein interactions, immunostaining and gene compensatory studies, investigating the mechanism underlying the effects of altered function of Eph family of receptor tyrosine kinases on phenotype.

A Novel Occulta-Type Spina Bifida Mediated by Murine Double Heterozygotes EphA2 and EphA4 Receptor Tyrosine Kinases.

Members of the Eph receptor tyrosine kinase have previously been implicated in cranial neural tube development. Failure of neural tube closure leads to the devastating conditions known as anencephaly and spina bifida. EphA2 and EphA4 are expressed at the tips of the closing spinal neural folds prior and during neural tube closure. We investigated the possible role of murine EphA2 and EphA4 during the last step of primary neural tube closure, which is adhesion and fusion. The individual mouse knockouts of EphA2 and EphA4 per se do not exhibit neural tube defects (NTDs). The embryos generated by the crossing of double heterozygotes Epha2tm1Jrui/+Epha4rb-2J/+ displayed NTDs with a wide degree of severity including close exencephaly and close spina bifida (spina bifida occulta). Interestingly, mutants displaying NTDs had skin covering the underlying lesion. The tissue sections revealed the elevated neural folds had not adhered and fused. The phenotypes seen in Epha2tm1Jrui/+Epha4rb-2J/+ double heterozygous embryos suggest both genes play a compensatory role with each other in the adhesion and fusion of the neural tube. In this study, there exists a >50% penetrance of NTDs in the mouse mutants, which genetically have a single allele each of EphA2 and EphA4 absent.

Spina Bifida: Pathogenesis, Mechanisms, and Genes in Mice and Humans.

Spina bifida is among the phenotypes of the larger condition known as neural tube defects (NTDs). It is the most common central nervous system malformation compatible with life and the second leading cause of birth defects after congenital heart defects. In this review paper, we define spina bifida and discuss the phenotypes seen in humans as described by both surgeons and embryologists in order to compare and ultimately contrast it to the leading animal model, the mouse. Our understanding of spina bifida is currently limited to the observations we make in mouse models, which reflect complete or targeted knockouts of genes, which perturb the whole gene(s) without taking into account the issue of haploinsufficiency, which is most prominent in the human spina bifida condition. We thus conclude that the need to study spina bifida in all its forms, both aperta and occulta, is more indicative of the spina bifida in surviving humans and that the measure of deterioration arising from caudal neural tube defects, more commonly known as spina bifida, must be determined by the level of the lesion both in mouse and in man.

The Prevalence and Distribution of Spina Bifida in a Single Major Referral Center in Malaysia.

BACKGROUND: The aim of this study is to review the medical history of patients with spina bifida, encompassing both aperta and occulta types born between the years 2003 until 2016, spanning a 13-year time period. We assessed each patient and maternal parent information, details of the defects, and conditions associated with the primary defect. We also include information on patients' ambulation and education level (where available). METHODS: Data from the Department of Patient Information University of Malaya Medical Centre (UMMC), Malaysia was captured from spina bifida patients (ICD10: Q05 spina bifida). Data involved patients referred to UMMC between 2003 and 2016 and/or born in UMMC within that particular time frame. We filtered and extracted the information according to the data of clinical examination, medical review, and social history provided in the medical records. RESULTS: A total of 86 patient records with spina bifida were analyzed. Spina bifida prevalence rate in this study ranged from 1.87 to 8.9 per 1,000 live births depending on weightage. We note that ethnicity was a factor whereby the highest numbers of spina bifida were from Malays (n = 36, 41.86%), followed by equal numbers of Chinese and Indians (n = 24, 27.91%). The highest number of diagnoses reported was myelomeningocele type-spina bifida (n = 39, 45.35%). The most common site of the spina bifida lesion was located at the lumbar region irrespective of aperta or occulta types (n = 23, 26.74%). Data on other associated phenotypes of spina bifida such as hydrocephalus and encephalocele was also captured at 37.21% (n = 32) and 1.16% (n = 1), respectively. In terms of mobility, 32.84% (n = 22/67) of patients between the ages 4 and 16 years old were found to be mobile. As many as 36.07% of patients ranging from 5 to 16 years of age (n = 22/61) received formal education ranging from preschool to secondary school. CONCLUSION: The prevalence of spina bifida in UMMC is as according to international statistics which is in the range of 0.5-10 per 1,000 live births. Majority of the reported cases were males, Malays, full term babies, and of the myelomeningocele phenotype located at the lumbar region.