I worked with mouse model of bladder cancer, and it took us some time to grow such model in our lab (as we first tried to do so with rats). Now we had checked the expression of apoptosis proteins in the cancer, and we didn’t find anything relevant with this molecule I’ve been working on. I am now in a fourth year of my PhD and deadlines are near, so I would like to publish something so that all of the work is not in vain. My mentor is against it and I am looking for something to persuade him. What can I do?
Your negative results are important because they would contribute important evidence in the concrete research field and would stop others doing following this direction of research that would just waste money and resources. That is why it is important to publish negative results. You can look up the Lancet series on research waste, or check this article on publication bias in animal research. This should give you enough arguments for the discussion with your mentor.