Smirnov AV, Shnaider TА, Korablev AN, Yunusova AM, Serova IA, Battulin NR. A hypomorphic mutation in the mouse Csn1s1 gene generated by CRISPR/Cas9 pronuclear microinjection.
Vavilovskii Zhurnal Genet Selektsii 2021;
25:331-336. [PMID:
34901729 PMCID:
PMC8627868 DOI:
10.18699/vj21.036]
[Citation(s) in RCA: 2] [Impact Index Per Article: 0.7] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/22/2020] [Revised: 01/28/2021] [Accepted: 02/08/2021] [Indexed: 11/19/2022] Open
Abstract
Caseins are major milk proteins that have an evolutionarily conserved role in nutrition. Sequence variations in the
casein genes affect milk composition in livestock species. Regulatory elements of the casein genes could be used to direct
the expression of desired transgenes into the milk of transgenic animals. Dozens of casein alleles have been identified for
goats, cows, sheep, camels and horses, and these sequence variants are associated with altered gene expression and milk
protein content. Most of the known mutations affecting casein genes’ expression are located in the promoter and 3’-untranslated regions. We performed pronuclear microinjections with Cas9 mRNA and sgRNA against the first coding exon of
the mouse Csn1s1 gene to introduce random mutations in the α-casein (Csn1s1) signal peptide sequence at the beginning
of the mouse gene. Sanger sequencing of the founder mice identified 40 mutations. As expected, mutations clustered
around the sgRNA cut site (3 bp from PAM). Most of the mutations represented small deletions (1–10 bp), but we detected
several larger deletions as well (100–300 bp). Functionally most mutations led to gene knockout due to a frameshift or a
start codon loss. Some of the mutations represented in-frame indels in the first coding exon. Of these, we describe a novel
hypomorphic Csn1s1 (Csn1s1c.4-5insTCC) allele. We measured Csn1s1 protein levels and confirmed that the mutation has a
negative effect on milk composition, which shows a 50 % reduction in gene expression and a 40–80 % decrease in Csn1s1
protein amount, compared to the wild-type allele. We assumed that mutation affected transcript stability or splicing by an
unknown mechanism. This mutation can potentially serve as a genetic marker for low Csn1s1 expression.
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