Abstract
Microphthalmia in sheep is an autosomal recessive inherited congenital anomaly found within the Texel breed. It is characterized by extremely small or absent eyes and affected lambs are absolutely blind. For the first time, we use a genome-wide ovine SNP array for positional cloning of a Mendelian trait in sheep. Genotyping 23 cases and 23 controls using Illumina's OvineSNP50 BeadChip allowed us to localize the causative mutation for microphthalmia to a 2.4 Mb interval on sheep chromosome 22 by association and homozygosity mapping. The PITX3 gene is located within this interval and encodes a homeodomain-containing transcription factor involved in vertebrate lens formation. An abnormal development of the lens vesicle was shown to be the primary event in ovine microphthalmia. Therefore, we considered PITX3 a positional and functional candidate gene. An ovine BAC clone was sequenced, and after full-length cDNA cloning the PITX3 gene was annotated. Here we show that the ovine microphthalmia phenotype is perfectly associated with a missense mutation (c.338G>C, p.R113P) in the evolutionary conserved homeodomain of PITX3. Selection against this candidate causative mutation can now be used to eliminate microphthalmia from Texel sheep in production systems. Furthermore, the identification of a naturally occurring PITX3 mutation offers the opportunity to use the Texel as a genetically characterized large animal model for human microphthalmia.
Highlights
Human microphthalmia, characterized by small eyes and other ocular abnormalities in newborns, is highly variable with the most severe cases anophthalmic [1,2]
Morphological studies showed that impaired lens formation seems to be the major cause of anophthalmia and microphthalmia, the precise pathogenesis of these phenotypes remains unknown [3]
Analyzing inherited isolated microphthalmia/anophthalmia in humans revealed a total of eight genes (SOX2, PAX6, OTX2, RAX, CHX10, FOXE3, PITX3, CRYBA4) carrying causative mutations [4,5,6,7,8,9,10,11]
Summary
Human microphthalmia, characterized by small eyes and other ocular abnormalities in newborns, is highly variable with the most severe cases anophthalmic [1,2]. Mutation Analysis We designed PCR primers for the amplification of a 14.5 kb segment containing the entire PITX3 gene and determined the genomic sequence of four microphthalmia affected and four healthy control sheep. This analysis revealed just a single sequence polymorphism (Figure 3A). This non-synonymous SNP located in PITX3 exon 4 (c.338G.C; Figure 3B) showed perfect association to the microphthalmia phenotype (Table 1). No size difference or alternative splicing was detected and analyzing the ORF of four individuals, two homozygous and two heterozygous for the associated INRA81 microsatellite allele, respectively, revealed no polymorphisms affecting the amino acid sequence of PAX2
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
