ABCA12
| Gene Symbol | Abca12 |
| Gene Name | Adenosine Tri Phosphate Binding Cassette Subfamily A Member 12 |
| Gene Synonym(s) | 4832428G11Rik, 4833417A11Rik |
| ENSEMBL | human: ENSG00000144452 mouse: ENSMUSG00000050296 |
| Allele Symbol | C57BL/6NCrl-Abca12em1(P23P)Ccpcz |
| Allele Name | endonuclease-mediated allele 1, Ccpcz |
| Allele Type | synonymous point mutation, P23P |
| Genomic location | human: Chromosome 2: 214,931,542-215,138,626 reverse strand, GRCh38:CM000664.2 mouse: Chromosome 1: 71,281,435-71,454,069 reverse strand, GRCm39:CM000994.3 |
| Strain of Origin | C57Bl/6N |
| Molecular Note | Mutation introduced by CRISPR/Cas9 double strand break and electroporation of dsDNA template with >40 bp homologous arms. Genotyped by PCR amplification of the sequence surrounding the mutation site and subsequent restriction digest by BsrFI as well as Sanger sequencing. |
| Mutations Made by | Czech Centre of Phenogenomics, Institute of Molecular Genetics of the Czech Academy of Sciences |
Description
The ABCA12 protein is a member of the ABC transporter superfamily, which utilises energy from ATP hydrolysis to move substrates across cell membranes. It is primarily localised in the lamellar granules of keratinocytes in the upper layers of the epidermis. Its primary role is the transport of glucosylceramides (long-chain lipids) into these lamellar granules. Once the granules fuse with the cell membrane, they release these lipids into the extracellular space, forming intercellular lipid layers. This creates the vital permeability skin barrier that prevents dehydration, handles thermoregulation, and protects the body against environmental pathogens (Sakai et al., 2007).
Associated pathology
Harlequin ichthyosis (HI)
Mutations in the ABCA12 gene can also result in Lamellar ichthyosis, Ichthyosis erythroderma and Congenital ichthyosis of other types, but both mouse models currently present in CCP are mimicking Harlequin ichthyosis (HI).
Loss-of-function mutations in the gene ABCA12 lead to Harlequin ichthyosis. The HI neonate is born with a critical condition characterised by excessively thickened skin that tends to crack, making it more susceptible to infections and moisture loss. Patients often suffer ectropion (lower eyelid turned outward), partially fused fingers, and eclabium (lip turned outward). Many children are born prematurely (around 35 weeks of pregnancy). However, even very serious forms of HI are not detected prenatally, as slightly fused fingers or eclabium and pre-clabium are not always recognisable. The survival rate in the postnatal period is about 56%. Patients often die in the first 1 or 2 weeks of life, but it mainly depends on the environment – level of sterile conditions, health care and on the specific mutation. Alterations in calcium-mediated signalling and protein phosphatase activity have also been reported in HI keratinocytes. Protease levels, such as calpain I, decrease in the skin of HI patients. The current management of HI involves daily application of emollients and, in more severe instances, systemic treatment with oral retinoids, which have unfavourable secondary effects. ABCA12 also has an effect that goes beyond the epidermis, and proteins from this family also play role in resistance to chemotherapy. (Akiyama, 2010, 2014; Yanagi et al., 2010)
Model Development
We used a synthetic ssODN carrying the target P23P synonymous mutation (c.69G>A) with >40 bp homologous arms. Used ssODN was premixed with Cas9 protein and gRNA and electroporated into zygotes. Zygotes or 2-cell stage embryos were transferred into pseudopregnant recipient mice. Resulting mice (G0 generation) were genotyped by PCR and subsequent restriction digest. The presence of P23P synonymous mutation, and no other mutations in the vicinity of targeted region, was confirmed by Sanger sequencing. Positive individuals were backcrossed with C57BL/6NCrl for two generations to establish the colony.