A 3.7 Mb Deletion Encompassing ZEB2 Causes a Novel Polled and Multisystemic Syndrome in the Progeny of a Somatic Mosaic Bull

Abstract

Polled and Multisystemic Syndrome (PMS) is a novel developmental disorder occurring in the progeny of a single bull. Its clinical spectrum includes polledness (complete agenesis of horns), facial dysmorphism, growth delay, chronic diarrhea, premature ovarian failure, and variable neurological and cardiac anomalies. PMS is also characterized by a deviation of the sex-ratio, suggesting male lethality during pregnancy. Using Mendelian error mapping and whole-genome sequencing, we identified a 3.7 Mb deletion on the paternal bovine chromosome 2 encompassing ARHGAP15, GTDC1 and ZEB2 genes. We then produced control and affected 90-day old fetuses to characterize this syndrome by histological and expression analyses. Compared to wild type individuals, affected animals showed a decreased expression of the three deleted genes. Based on a comparison with human Mowat-Wilson syndrome, we suggest that deletion of ZEB2, is responsible for most of the effects of the mutation. Finally sperm-FISH, embryo genotyping and analysis of reproduction records confirmed somatic mosaicism in the founder bull and male-specific lethality during the first third of gestation. In conclusion, we identified a novel locus involved in bovid horn ontogenesis and suggest that epithelial-to-mesenchymal transition plays a critical role in horn bud differentiation. We also provide new insights into the pathogenicity of ZEB2 loss of heterozygosity in bovine and humans and describe the first case of male-specific lethality associated with an autosomal locus in a non-murine mammalian species. This result sets PMS as a unique model to study sex-specific gene expression/regulation.

Independent Polled Mutations Leading to Complex Gene Expression Differences in Cattle

“…Recently, a SNP within intron 3 of IFGR2 has been described to be in perfect association with polledness in Holstein cattle by another group [16]. A further dominantly inherited polled phenotype accompanied by congenital malformations has been shown to be caused by a ZEB2 mutation in French Charolais cattle [17]. This report confirms the assumption that other mutations beside the characterized polled alleles on BTA 1 may affect horn growth in cattle.…”

Novel Insights into the Bovine Polled Phenotype and Horn Ontogenesis in Bovidae

“…As previously observed [20], histological sections of wt horn buds were characterized by three main features as compared with wt frontal skin: clusters of dermal cells displaying glandular/ductal differentiation, supernumerary layers of vacuolated keratinocytes and absence of hair follicle germs (Figs. 4A–4C, 4N and 4O).…”

“…While neither of them is located on chromosome one in bovines, it is striking to note that these genes are paralog to FOXL2 and TWIST1 , respectively, which are associated with goat PIS [24] and bovine T2SS [23]. Moreover, they both encode transcription factors that are able to promote EMT [35]–[37] like TWIST1 and ZEB2 , which is associated with a third horn defect syndrome in bovines: PMS [20]. Finally, complete deficiency of TWIST2 in humans and mice causes bitemporal skin lesions (characterized by hypoplastic dermis and the absence of subcutaneous fat and epidermal appendages) [38], unraveling an evolutionary conserved cryptic expression of this gene in mammals at the exact anatomical location of horns in Bovidae and constituting an additional argument in favor of a possible role of TWIST2 in horn ontogenesis.…”

“…While the Polled mutation has been easily mapped on bovine chromosome 1 (BTA01) in more than ten breeds [11]–[17], fine characterization of this locus has proved more difficult than expected and, to date, neither the causal mutation(s) nor the molecular etiology of this phenotype have been definitively identified. Among the major issues encountered in this process are: (i) the lack of appropriate (i.e., horned) model species, which make it impossible to identify functional candidate genes from previous studies; (ii) the absence of candidate polymorphisms in the coding sequences of any of the positional candidate genes [18]–[20]; and (iii) the absence of differential expression of the same genes between horn buds from polled and horned newborn calves [21].…”

“…The Polled and Multisystemic Syndrome (PMS) and the Type 2 Scurs Syndrome (T2SS) were described, and their causative mutations highlighted the critical role played by ZEB2 and TWIST1 genes, two master regulators of epithelial-to-mesenchymal transition (EMT), in bovine horn bud differentiation [20], [23]. Nevertheless, we were not able to find a direct link between these two genes and any of the genes located in caprine ( FOXL2 , PISRT1 and PFOXic ) [24], [25], ovine ( RXFP2 ) [26] or bovine ( IL10RB , IFNAR2 , OLIG1 and OLIG2 ) [19], [22] Polled regions.…”