I really would start with the protocol from the manufacturer:

https://www.thermofisher.com/au/en/home/references/protocols/nucleic-acid-purification-and-analysis/rna-protocol/genomic-dna-preparation-from-rnalater-preserved-tissues.html

The most important part of the entire process is the Proteinase K step. Make sure you digest for long enough and keep it moving as much as possible. I have received very sub-par results with incomplete digestion of the tissue.

Thank you Sophie. This protocol mentions use of 750ul of 50:50 phenol-chloroform. Does it mean we need to mix phenol and chloroform together in 1:1 ratio (375ul phenol + 375ul chloroform) and then add in the tube or we can add phenol (375ul) and chloroform (375ul) separately in equal volume in the tube? Please clarify. Thanks.

Sachin - you can do it either way. The end result is the same. Remember to perform this step in a fume hood.

Thank you Sophie. Appreciate it.

Dear Huang,

Thank you for your response. There are many column based DNA extraction kits, from Qiagen, Progmega etc. Are they all compatible with tissue stored in RNA later for DNA isolation? 

Sachin, tissue has to incuvpbated with the RNAlater at 4 Celsius overnight prior to the minus 80. It takes time fir the RNAlater to get into the tissue like lung even though its porous.

Thank you Hsiao.

hi. Dr. Sachin Kumar

i suggest you these:-

1- Genomic DNA Preparation from RNAlater™ Preserved Tissues

https://www.thermofisher.com/in/en/home/references/protocols/nucleic-acid-purification-and-analysis/rna-protocol/genomic-dna-preparation-from-rnalater-preserved-tissues.html

2-Genomic DNA extraction from tissues animal

https://www.kurabo.co.jp/bio/biodocument/eng/QuickGene_Application_Data_DA-b_Genomic%20DNA%20Extraction%20from%20Tissue%20of%20Animal.pdf

3- A simple, rapid method for isolation of high quality genomic DNA from animal tissues

https://academic.oup.com/nar/article-abstract/23/24/5087/2400744?redirectedFrom=PDF

good luck