It’s a surprising thing when a mother mouse kills all of her baby mice. We found a mutant line of mice displaying waddling gaits a half year ago. The mice did not show specific characters until they gave birth to baby mice. Most of the waddling mother mice did not nurse their babies; moreover, they ate their babies. At the beginning we used surrogate mothers to nurse the descendants of the waddling mice. Later on, we found some waddling mother mice would nurse her neonates if the environment was kept absolutely quiet and their cages were not disturbed at all. My assistants and I had to get into the animal room slowly, quietly and stealthily. Instead of lifting off the covers and looking down in the cages, we watched the mother mice and their babies laterally through the partially transparent cages. However, our sight was usually blocked by the mother mice or stacked beddings. It was almost impossible to learn if all the baby mice were still alive. What we could do was judge from the mother mice’s posture to determine if they were nursing their babies. The observation difficulty waned with the growth of baby mice day by day. It was a joy to see our baby mice grow bigger and find our strategy was a success. Along with the growth of the baby mice, the beddings became messy and smelly; however, we decided to keep up our ‘quiet and safe’ strategy and did not disturb them by changing the beddings.
     Everything seemed to be going well until a desperate shriek was uttered from an assistant, who found all the 12-day-old baby mice were killed by their mother. How come a mother would kill her own baby? Though this kind of mouse have been well known of poor–maternity skills, which means they have a higher chance of failing to nurse their neonates, they never kill their own babies intentionally. It was further incomprehensible that a mother mouse killed all of her babies when she had ‘loved’ and nursed them for 12 days. Tragedy seldom goes alone. The same event happened on another waddling mother mouse a few days later. The first murderous mother had her second pregnancy and gave birth to another litter of mice. Even with our full attention, she killed four of her five babies at the age of 13 days, when the pups were just going to open up their eyes.
It is very natural in the animal kingdom that mothers nurse and protect their babies. Without this kind of natural maternity, a species is impossible to survive, not to mention the act of killing babies. How could we get a line of mice with such an incredible nature? We used a method of artificial mutagenesis to induce random mutation in the genome of C57BL mice. It’s possible that a genetic code that is responsible for maternity is disrupted. Most people must be amazed by this explanation. Could the great loving character of ‘maternity’ simply be a reachable and manipulativable genetic code? I’ll try to unveil the mystery of the relationship between maternity, the act of killing babies and the genetic code.
Hong CJ