Hexokinase 1 and 2 mediates glucose utilization to regulate the synthesis of kappa casein via ribosome protein subunit 6 kinase 1 in bovine mammary epithelial cells

Glucose plays a vital part in milk protein synthesis through the mTOR signaling pathway in bovine mammary epithelial cells(BMEC).The objectives of this study were to determine how glucose affects hexokinase(HK)activity in BMEC and investigate the regulatory effect of HK in kappa casein(CSN3)synthesis via the mechanistic target of rapamycin complex 1(mTORC1)signaling pathway in BMEC.For this,HK1 and HK2 were knocked out in BMEC using the CRISPR/Cas9 system.The gene and protein expression,glucose uptake,and cell proliferation were measured.We found that glucose uptake,cell proliferation,CSN3 gene expression levels,and expression of HK1 and HK2 increased with increasing glucose concentrations.Notably,glucose uptake was significantly reduced in HK2 knockout(HK2KO)BMEC treated with 17.5 mM glucose.Moreover,under the same glucose treatment conditions,the proliferative ability and abundance of CSN3 were significantly diminished in both HK1 knockout(HK1KO)and HK2KO BMEC compared with that in wild-type BEMC.We further observed that the phosphorylation levels of ribosome protein subunit 6 kinase 1(S6K1)were reduced in HK1KO and HK2KO BMEC following treatment with 17.5 mM glucose.As expected,the levels of glucose-6-phosphate and the m RNA expression levels of glycolysis-related genes were decreased in both HK1KO and HK2KO BMEC following glucose treatment.These results indicated that the knockout of HK1 and HK2 inhibited cell proliferation and CSN3 expression in BMEC under glucose treatment,which may be associated with the inactivation of the S6K1 and inhibition of glycolysis.

Comparing successful gene knock-in efficiencies of CRISPR/Cas9 with ZFNs and TALENs gene editing systems in bovine and dairy goat fetal fibroblasts

This study aimed to compare the efficiencies of clustered regulatory interspaced short palindromic repeat（CRISPR）/Cas9-mediated gene knock-ins with zinc finger nucleases（ZFNs） and transcription activator-like effector nucleases（TALENs） in bovine and dairy goat fetal fibroblasts. To test the knock-in efficiency, a set of ZFNs and CRISPR/Cas9 plasmids were designed to edit the bovine myostatin（MSTN） gene at exon 2, while a set of TALENs and CRISPR/Cas9 plasmids were designed for editing the dairy goat β-casein gene at exon 2. Donor plasmids utilizing the ZFNs, TALENs, and CRISPR/Cas9 cutting sites were constructed in theGFP-PGK-Neo R plasmid background, including a 5′ and 3′ homologous arm flanking the genes humanized Fat-1（h Fat-1） or enhanced green fluorescent protein（eGFP）. Subsequently, the ZFNs, TALENs, or CRISPR/Cas9 and thehFat-1 or eGFP plasmids were co-transfected by electroporation into bovine and dairy goat fetal fibroblasts. After G418（Geneticin） selection, single cells were obtained by mouth pipetting, flow cytometry or a cell shove. The gene knock-in events were screened by PCR across the homologous arms. The results showed that in bovine fetal fibrobalsts, the efficiencies of ZFNs-mediated eGFP andhFat-1 gene knock-ins were 13.68 and 0%, respectively. The efficiencies of CRISPR/Cas9-mediated eGFP andhFat-1 gene knock-ins were 77.02 and 79.01%, respectively. The eGFP gene knock-in efficiency using CRISPR/Cas9 was about 5.6 times higher than when using the ZFNs gene editing system. Additionally, thehFat-1 gene knock-in was only obtained when using the CRISPR/Cas9 system. The difference of knockin efficiencies between the ZFNs and CRISPR/Cas9 systems were extremely significant（P〈0.01）. In the dairy goat fetal fibroblasts, the efficiencies of TALENs-mediated eGFP andhFat-1 gene knock-ins were 32.35 and 26.47%, respectively. Theefficiencies of eGFP and hFat-1 gene knock-ins using CRISPR/Cas9 were 70.37 and 74.29%, respectively. The knock-in efficiencies difference between the TALENs and CRISPR/Cas9 systems were extremely significant（P〈0.01）. This study demonstrated that CRISPR/Cas9 was more efficient at gene knock-ins in domesticated animal cells than ZFNs and TALENs. The CRISPR/Cas9 technology offers a new era of precise gene editing in domesticated animal cell lines.