Genetic and stochastic influences upon tumor formation and tumor types in Li-Fraumeni mouse models

This study used mice heterozygous for Tp53 mutations with different genetic backgrounds to investigate the genetic or stochastic factors that modify the penetrance of tumor formation by Tp53 mutation.

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Thank you for this interesting contribution, we look forward to publishing your paper in Life Science Alliance. This manuscript by Chan et al describes an interesting genetic study to determine possible genetic and stochastic effects on tumor formation and the type of tumors that might be due to inherited mutant p53s often identified in Li-Fraumeni syndrome (LFS) patients by employing a genetically manipulated mouse model system that harbor Li-Fraumeni syndrome-derived p53 mutants. Their results demonstrate that p53 mutants have a strong impact on tumorigenesis and the type of tumors that are formed during this process, which somewhat mimics the LFS phenotype. This genetic study is interesting and important. Addressing the following minor points might help them improve their manuscript.
1. In the Abstract, the sentence "The genetic background of mice carrying Tp53 mutations has a strong influence upon the tissue type of the tumor produced as well as the formation of multiple tumors produced in a single mouse" repeats twice. Can this claim be more concisely expressed? 2. In Table 1, the most common tumors in mice are T-cell lymphomas, which are not found in humans with Li-Fraumeni syndrome. Is this because the mice are prone to grow lymphomas independent of p53 status? An explanation would be helpful.
3. Some opinions or points in this manuscript may need their related references: 1) Introduction: "Background also makes ... are predisposed to breast cancers"; 2) Result- Figure 1: "Based upon previous observations, this was done most intensively between 11 and 20 months after birth." Please either cite the result or a reference(s); 3) Result- Figure 4: To support the reason that the experiment was stopped at 20 months after birth. 4. Some proofs would be helpful to improve their presentation (such as pictures of H&E staining slides or tissues) of anatomical observation for Figures 1, 2 and 4). In this manuscript, Hu and colleagues cross R172H mice in a C57Bl/6 background to 7 other genetic backgrounds and they analyze the incidence and timing of cancer in the different F1 progeny. They report some fascinating differences: SWR and NOD strains develop cancer the latest, but SWR also has the highest incidence of cancer. F1 progeny crossed into A/J and NOD backgrounds have dramatically different median survivals, and Balb/c mice have a phenotype most closely resemblant, to this reviewer, to Li Fraumeni in humans (high rates of sarcoma, plus quite a bit of carcinoma, as well as high numbers of mice with multiple tumors). The authors conclude that the existence of dominant genetic modifiers in these different strains is likely at play; they also conservatively and correctly conclude that other differences, such as microbiome, gender/sexual dimorphism and epigenetics may also be factors in these differences. In all this manuscript is a very useful resource for individuals using GEMM models to assess the impact of p53 mutation on cancer. Two very minor changes are requested: 1. Figure 1 and 2 differ in that they are based on observational versus histopathological data, but the figures are related; I would like the authors to use the same colors and also to label each line, as done in Figure 1, in Figure   2. Page 11"This is the reason..." paragraph should be attached to the preceding paragraph (starts with C57Bl/6 mice) 3. Table 1: re-label "Incidence of tumor types" to be "Average incidence of tumor types" 1st Authors' response to Reviewers December 14, 2020 Following is our response to the comments from reviewers.
Reviewer #1 (Comments to the Authors (Required)): This manuscript by Chan et al describes an interesting genetic study to determine possible genetic and stochastic effects on tumor formation and the type of tumors that might be due to inherited mutant p53s often identified in Li-Fraumeni syndrome (LFS) patients by employing a genetically manipulated mouse model system that harbor Li-Fraumeni syndrome-derived p53 mutants. Their results demonstrate that p53 mutants have a strong impact on tumorigenesis and the type of tumors that are formed during this process, which somewhat mimics the LFS phenotype. This genetic study is interesting and important. Addressing the following minor points might help them improve their manuscript.
1. In the Abstract, the sentence "The genetic background of mice carrying Tp53 mutations has a strong influence upon the tissue type of the tumor produced as well as the formation of multiple tumors produced in a single mouse" repeats twice. Can this claim be more concisely expressed?
Response: Thank you for this good suggestion. We revised the sentence as following: The genetic background of mice carrying Tp53 mutations has a strong influence upon the tissue type of the tumor produced as well as the number of tumors formed in a single mouse. Table 1, the most common tumors in mice are T-cell lymphomas, which are not found in humans with Li-Fraumeni syndrome. Is this because the mice are prone to grow lymphomas independent of p53 status? An explanation would be helpful.

In
Response: This is a very good suggestion. It has been observed that some of the inbred strains, such as Balb/c and C57BL/6, are predisposed to developing certain spontaneous tumors, with lymphoma often being most common, indicating that the mouse and human T cell adaptive immune systems have a differential dependence upon p53 to prevent a lymphoma or leukemia (Kohnken R., et al. Front Oncol. 2017, 7:22). We have added this explanation in Page 7, 2 nd paragraph, line 4-8.