Conversion of a normal maize hybrid into a waxy version using in vivo CRISPR/Cas9 targeted mutation activity

Waxy maize is a specialty maize that produces mainly amylopectin starch with special food or industrial values. The objective of this study was to overcome the limitations of wx mutant allele acquisition and breeding efficiency by conversion of parental lines from normal to waxy maize. The intended mutation activity was achieved by in vivo CRISPR/Cas9 machinery involving desired-target mutation of the Wx locus in the ZC01 background,abbreviated as ZC01-DTM^(wx). Triple selection was applied to segregants to obtain high genome background recovery with transgene-free wx mutations. The targeted mutation was identified, yielding six types of mutations among progeny crossed with ZC01-DTM^(wx).The amylopectin contents of the endosperm starch in mutant lines and hybrids averaged94.9%, while those of the wild-type controls were significantly(P < 0.01) lower, with an average of 76.9%. Double selection in transgene-free lines was applied using the Bar strip test and Cas9 PCR screening. The genome background recovery ratios of the lines were determined using genome-wide SNP data. That of lines used as male parents was as high as98.19% and that of lines used as female parents was as high as 86.78%. Conversion hybrids and both parental lines showed agronomic performance similar to that of their wild-type counterparts. This study provides a practical example of the efficient extension of CRISPR/Cas9 targeted mutation to industrial hybrids for transformation of a recalcitrant species.

Antitumor and off-target effects of cholesterol-conjugated let-7a mimics in an orthotopic hepatocellular carcinoma xenograft nude mouse model

Objective: To explore the antitumor and potential off-target effects of systemically delivered cholesterol-conjugatedlet-7a mimics(Chol-let-7a) and control mimics(Chol-miRCtrl) on hepatocellular carcinomain vivo.Methods: The antitumor effects of two intravenous dosing regimens ofChol-let-7a on heptocellular carcinoma growth were compared using an orthotopic xenograft mouse model. Off-targets were analyzed with histopathological and ultrapathological features of heparenal tissue and cells in theChol-let-7a-, Chol-miRCtrl-, and saline-treated (blank) xenograft mice and normal control mice. Then,let-7a abundance in orthotopic tumors, corresponding paracancerous hepatic tissue, and normal liver tissue from healthy nude mice was examined by reverse transcription-polymerase chain reaction. The distribution ofChol-let-7a andChol-miRCtrl in vivo was examined by whole-animal imaging and frozen-sections observation. The experiments were approved by the Institutional Research Board of Peking Union Medical College Hospital.Results: Continuous treatment withChol-let-7a resulted in tumors that were 35.86% and 40.02% the size of those in theChol-miRCtrl and blank xenograft group (P < 0.01 andP < 0.01, respectively), while intermittent dosing withChol-let-7a resulted in tumors that were 65.42% and 56.66% the size of those in theChol-miRCtrl and the blank control group, respectively (P < 0.05 andP < 0.05). In addition, some histopathological and ultrapathological features were only observed after treatment with the two cholesterol-conjugated molecules, however mild with intermittent dosingChol-let-7a treatment, such as diffuse sinusoidal dilation and edema, primarily around the centrolobular vein in heptic tissues;mild hypercellularity with dilated capillary lumens in the renal tissue;and some organelle abnormalities found in heptic and renal cells. Furthermore, whole-animal imaging showed thatChol-let-7a andChol-miRCtrl were predominantly distributed in the liver, kidney, and bladder regions after injection, and that the concentration ofChol-let-7a andChol-miRCtrl in the kidney and the bladder decreased much slowly in the xenograft animals, especially in theChol-miRCtrl group. Finally, RT-PCR analysis showed thatlet-7a levels were significantly increased in Chol-let-7a-treated xenografts compared withChol-miRCtrl group (P=0.003) and blank xenograft group (P=0.001);however, the level was only equivalent to 50.6% and 40.7% of that in paracancerous hepatic tissue and hepatic tissue in normal mice, respectively.Conclusions: Chol-let-7a, administered either continuously or intermittently, showed effective antitumor efficacy.Chol-let-7a had some off-target effects, such as mild acute hepatitis-like inflammation and non-specific drug-induced kidney injury. The intermittent dosing regimen resulted in less damage than the continuous regimen, while maintaining relatively satisfactory antitumor efficacy, which could be useful for the investigation and possible clinical use of miRNA treatment regimens in the future.