Znanstvena istraživanja u 21. stoljeću - etički aspekti uporabe laboratorijskih životinja i alternativni modeli

U toksikološkim istraživanjima uz uporabu klasičnih (in vivo) istraživanja, primjenjuju se alternativni test sustavi. Korištenje laboratorijskih životinja, embrija, humanog i animalnog tkiva, kultura stanica i fetalnog seruma u istraživanjima smatra se etički problematičnim te se ograničava zakonima, pravilnicima i praksom. Razmatranjem načina kojima bi se neetičnost mogla izbjeći, došlo je do razvoja “3R” načela (akronim za tri pristupa koja bi se trebala provoditi pri istraživanjima na laboratorijskim životinjama), a to su: smanjenje/racionalizacija uporabe laboratorijskih životinja (engl. Reduction), načelo njihove zamjene (engl. Replacement) i poboljšanje uvjeta uzgoja, smještaja i skrbi za životinje (engl. Refinement). Većina je alternativnih testova toksičnosti još uvijek u postupku validacije. Pojedini in vitro testovi za istraživanja embriotoksičnosti (etički posebno osjetljivo područje) koja su priznala nadležna regulatorna tijela, su EST (engl. Embryonic Stem cell Test), WEC (engl. Whole- Embryo Culture) i MM (engl. MicroMass) test. Standardizacija protokola i uvođenje novih in vitro modela predstavlja važan segment napretka u toksikološkim istraživanjima. Znanstvena budućnost tu vidi mogućnost razvoja i implementacije načela etičnosti u istraživanja primjenjujući sustave koji će promišljeno i bez korištenja živih organizama dijelom nadomjestiti metode u biomedicini, veterinarskoj medicini, biotehnologiji i užem smislu - toksikologiji i farmakologiji.

Understanding the source of METTL3-independent m6A in mRNA

N6-methyladenosine (m6A) is a highly prevalent mRNA modification which promotes degradation of transcripts encoding proteins that have roles in cell development, differentiation, and other pathways. METTL3 is the major methyltransferase that catalyzes the formation of m6A in mRNA. As 30—80% of m6A can remain in mRNA after METTL3 depletion by CRISPR/Cas9-based methods, other enzymes are thought to catalyze a sizable fraction of m6A. Here, we re-examined the source of m6A in the mRNA transcriptome. We characterized mouse embryonic stem cell lines which continue to have m6A in their mRNA after Mettl3 knockout. We show that these cells express alternatively spliced Mettl3 transcript isoforms that bypass the CRISPR/Cas9 mutations and produce functionally active methyltransferases. We similarly show that other reported METTL3 knockout cell lines express altered METTL3 proteins. We find that gene dependency datasets show that most cell lines fail to proliferate after METTL3 deletion, suggesting that reported METTL3 knockout cell lines express altered METTL3 proteins rather than have full knockout. Finally, we reassessed METTL3's role in synthesizing m6A using a genomic deletion of Mettl3, and found that METTL3 is responsible for >95% of m6A in mRNA. Overall, these studies suggest that METTL3 is responsible for the vast majority of m6A in the transcriptome, and that remaining m6A in putative METTL3 knockout cell lines is due to the expression of altered but functional METTL3 isoforms.

Effect of NANOG overexpression on porcine embryonic development and pluripotent embryonic stem cell formation in vitro

Summary The efficiency of establishing pig pluripotent embryonic stem cell clones from blastocysts is still low. The transcription factor Nanog plays an important role in maintaining the pluripotency of mouse and human embryonic stem cells. Adequate activation of Nanog has been reported to increase the efficiency of establishing mouse embryonic stem cells from 3.5 day embryos. In mouse, Nanog starts to be strongly expressed as early as the morula stage, whereas in porcine NANOG starts to be strongly expressed by the late blastocyst stage. Therefore, here we investigated both the effect of expressing NANOG on porcine embryos early from the morula stage and the efficiency of porcine pluripotent embryonic stem cell clone formation. Compared with intact porcine embryos, NANOG overexpression induced a lower blastocyst rate, and did not show any advantages for embryo development and pluripotent embryonic stem cell line formation. These results indicated that, although NANOG is important pluripotent factor, NANOG overexpression is unnecessary for the initial formation of porcine pluripotent embryonic stem cell clones in vitro.