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Evaluation of the α-casein (CSN1S1) locus as a potential target for a site-specific transgene integration. Sci Rep 2022; 12:7983. [PMID: 35568783 PMCID: PMC9107462 DOI: 10.1038/s41598-022-12071-1] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 11/06/2021] [Accepted: 04/29/2022] [Indexed: 11/25/2022] Open
Abstract
Transgenic animals are an important tool in biotechnology, including the production of recombinant proteins in the milk. Traditionally, expression constructs are based on hybrid vectors bearing mammary gland specific regulatory elements from the α-casein (Csn1s1), β-casein (Csn2), whey acidic protein (WAP), or β-lactoglobulin (BLG) genes. Overexpression from the randomly integrated vectors typically provides high levels of expression, but has drawbacks due to unpredictable genome localization. CRISPR-Cas9 targeted transgene integration into the endogenous casein locus could alleviate the need for extensive animal screening to achieve high and reproducible expression levels. We decided to evaluate such a “precise” integration approach, placing the human granulocyte–macrophage colony-stimulating factor (hGMCSF) gene under control of the mouse endogenous alpha-S1-casein (Csn1s1) promoter. We designed two types of transgene integrations: a knock-in in the second exon of the Csn1s1 (INS-GM) and a full-size Csn1s1 replacement with hGMCSF (REP-GM) which was never tested before. The INS-GM approach demonstrated low transgene expression and milk protein levels (0.4% of Csn2 transcripts; 2–11 µg/ml hGMCSF). This was probably caused by the absence of the 3’-polyadenylation signal in the hGMCSF transgene. REP-GM animals displayed high transgene expression, reaching and slightly exceeding the level of the endogenous Csn1s1 (30–40% of Csn2 transcripts), but yielded less hGMCSF protein than expected (0.2–0.5 mg/ml vs 25 mg/ml of Csn1s1), indicating that translation of the protein is not optimal. Homozygous inserts leading to the Csn1s1 knock-out did not have any long standing effects on the animals’ health. Thus, in our experimental design, site-specific transgene integration into the casein locus did not provide any significant advantage over the overexpression approach.
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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] [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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Affiliation(s)
- A V Smirnov
- Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
| | - T А Shnaider
- Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
| | - A N Korablev
- Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
| | - A M Yunusova
- Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
| | - I A Serova
- Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia
| | - N R Battulin
- Institute of Cytology and Genetics of the Siberian Branch of the Russian Academy of Sciences, Novosibirsk, Russia Novosibirsk State University, Novosibirsk, Russia
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Smirnov A, Fishman V, Yunusova A, Korablev A, Serova I, Skryabin BV, Rozhdestvensky TS, Battulin N. DNA barcoding reveals that injected transgenes are predominantly processed by homologous recombination in mouse zygote. Nucleic Acids Res 2020; 48:719-735. [PMID: 31740957 PMCID: PMC7145541 DOI: 10.1093/nar/gkz1085] [Citation(s) in RCA: 15] [Impact Index Per Article: 3.8] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/25/2019] [Revised: 10/29/2019] [Accepted: 11/05/2019] [Indexed: 12/14/2022] Open
Abstract
Mechanisms that ensure repair of double-strand DNA breaks (DSBs) are instrumental in the integration of foreign DNA into the genome of transgenic organisms. After pronuclear microinjection, exogenous DNA is usually found as a concatemer comprising multiple co-integrated transgene copies. Here, we investigated the contribution of various DSB repair pathways to the concatemer formation. We injected mouse zygotes with a pool of linear DNA molecules carrying unique barcodes at both ends and obtained 10 transgenic embryos with 1–300 transgene copies. Sequencing the barcodes allowed us to assign relative positions to the copies in concatemers and detect recombination events that occurred during integration. Cumulative analysis of approximately 1,000 integrated copies reveals that over 80% of them underwent recombination when their linear ends were processed by synthesis-dependent strand annealing (SDSA) or double-strand break repair (DSBR). We also observed evidence of double Holliday junction (dHJ) formation and crossing over during the concatemer formations. Sequencing indels at the junctions between copies shows that at least 10% of DNA molecules introduced into the zygotes are ligated by non-homologous end joining (NHEJ). Our barcoding approach, verified with Pacific Biosciences Single Molecule Real-Time (SMRT) long-range sequencing, documents high activity of homologous recombination after DNA microinjection.
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Affiliation(s)
| | - Veniamin Fishman
- Institute of Cytology and Genetics SB RAS, Novosibirsk, Russia.,Novosibirsk State University, Novosibirsk, Russia
| | | | - Alexey Korablev
- Institute of Cytology and Genetics SB RAS, Novosibirsk, Russia
| | - Irina Serova
- Institute of Cytology and Genetics SB RAS, Novosibirsk, Russia
| | - Boris V Skryabin
- Medical Faculty, Core Facility Transgenic animal and genetic engineering Models (TRAM), University of Muenster, Muenster, Germany
| | - Timofey S Rozhdestvensky
- Medical Faculty, Core Facility Transgenic animal and genetic engineering Models (TRAM), University of Muenster, Muenster, Germany
| | - Nariman Battulin
- Institute of Cytology and Genetics SB RAS, Novosibirsk, Russia.,Novosibirsk State University, Novosibirsk, Russia
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Transcription termination sequences support the expression of transgene product secreted with milk. Transgenic Res 2019; 28:401-410. [PMID: 30919251 DOI: 10.1007/s11248-019-00122-9] [Citation(s) in RCA: 3] [Impact Index Per Article: 0.6] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 08/03/2018] [Accepted: 03/12/2019] [Indexed: 01/04/2023]
Abstract
Expression of the reporter gene in transgenic animals depends on the surrounding chromatin environment. Recent genome-wide studies have shown that, in mammals, the entire genome is transcribed. Transcription through a transgene often has a negative effect on the expression of a reporter gene. Here, we compared the ability of well-studied chicken chromatin insulator HS4 and bidirectional transcription terminators from the human genome to support high-level expression of the firefly luciferase gene (Fluc) under control of the previously characterized goat β-casein gene promoter. The insertion of HS4 or either of the two transcription terminators upstream of the promoter resulted in tenfold enhancement of Fluc expression in the mammary glands of transgenic mice. These results suggest that transcriptional terminators, similar to the HS4 insulator, can be used to improve the reporter gene expression in transgenic animals.
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Smirnov AV, Kontsevaya GV, Feofanova NA, Anisimova MV, Serova IA, Gerlinskaya LA, Battulin NR, Moshkin MP, Serov OL. Unexpected phenotypic effects of a transgene integration causing a knockout of the endogenous Contactin-5 gene in mice. Transgenic Res 2017; 27:1-13. [PMID: 29264679 DOI: 10.1007/s11248-017-0053-y] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 09/04/2017] [Accepted: 12/01/2017] [Indexed: 01/06/2023]
Abstract
Contactins (Cntn1-6) are a family of neuronal membrane proteins expressed in the brain. They are required for establishing cell-to-cell contacts between neurons and for the growth and maturation of the axons. In humans, structural genomic variations in the Contactin genes are implicated in neurodevelopmental disorders. In addition, population genetic studies associate Contactins loci with obesity and hypertension. Cntn5 knockout mice were first described in 2003, but showed no gross physiological or behavioral abnormalities (just minor auditory defects). We report a novel Cntn5 knockout mouse line generated by a random transgene integration as an outcome of pronuclear microinjection. Investigation of the transgene integration site revealed that the 6Kbp transgene construct coding for the human granulocyte-macrophage colony-stimulating factor (hGMCSF) replaced 170 Kbp of the Cntn5 gene, including four exons. Reverse transcription PCR analysis of the Cntn5 transcripts in the wild-type and transgenic mouse lines showed that splicing of the transgene leads to a set of chimeric hGMCSF-Cntn5 transcript variants, none of which encode functional Cntn5 protein due to introduction of stop codons. Although Cntn5 knockout animals displayed no abnormalities in behavior, we noted that they were leaner, with less body mass and fat percentage than wild-type animals. Their cardiovascular parameters (heart rate, blood pressure and blood flow speed) were elevated compared to controls. These findings link Cntn5 deficiency to obesity and hypertension.
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Affiliation(s)
- Alexander V Smirnov
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia.
| | - Galina V Kontsevaya
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Natalia A Feofanova
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Margarita V Anisimova
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Irina A Serova
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Lyudmila A Gerlinskaya
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Nariman R Battulin
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia.,Novosibirsk State University, Novosibirsk, Russia
| | - Mikhail P Moshkin
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia
| | - Oleg L Serov
- Federal Research Center Institute of Cytology and Genetics, Siberian Division of the Russian Academy of Sciences, Novosibirsk, Russia. .,Novosibirsk State University, Novosibirsk, Russia.
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Intron V, not intron I of human thrombopoietin, improves expression in the milk of transgenic mice regulated by goat beta-casein promoter. Sci Rep 2015; 5:16051. [PMID: 26527459 PMCID: PMC4630608 DOI: 10.1038/srep16051] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Received: 07/09/2015] [Accepted: 09/25/2015] [Indexed: 11/29/2022] Open
Abstract
Introns near 5′ end of genes generally enhance gene expression because of an enhancer /a promoter within their sequence or as intron-mediated enhancement. Surprisingly, our previous experiments found that the vector containing the last intron (intron V) of human thromobopoietin (hTPO) expressed higher hTPO in cos-1 cell than the vector containing intron I regulated by cytomegalovirus promoter. Moreover, regulated by 1.0 kb rat whey acidic protein promoter, hTPO expression was higher in transgenic mice generated by intron V-TPOcDNA than in transgenic mice generated by TPOcDNA and TPOgDNA. However, it is unknown whether the enhancement of hTPO expression by intron I is decreased by uAUG7 at 5′-UTR of hTPO in vivo. Currently, we constructed vectors regulated by stronger 6.5kb β-casein promoter, including pTPOGA (containing TPOcDNA), pTPOGB (containing TUR-TPOcDNA, TUR including exon1, intron I and non-coding exon2 of hTPO gene), pTPOGC (containing ΔTUR-TPOcDNA, nucleotides of TUR from uAUG7 to physiological AUG were deleted), pTPOGD (containing intron V-TPOcDNA) and pTPOGE (containing TPOgDNA), to evaluate the effect of intron I on hTPO expression and to further verify whether intron V enhances hTPO expression in the milk of transgenic mice. The results demonstrated that intron V, not intron I improved hTPO expression.
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