Biological Sciences

Muriel N. Nesbitt Associate Professor of Biology, UCSD e-mail: mnesbitt@ucsd.edu

     My initial research interest was in X-chromosome inactivation in the mouse. X inactivation gives rise to mosaicism arising very early in mammalian embryonic development, and my interest was in using this cell-level mosaicism to trace the fates of various cell populations during development.¹ This led to an interest in other kinds of cell-level markers, particularly in mouse chimeras made by morula aggregation, and to an expanded idea of what phenomena beyond cell migration patterns could be studied. 

In the establishment of inbred strains of mice, genetic differences affecting behavior became fixed unintentionally. Some of these behavior differences are genetically very complex. I became interested in using chimeric mice to study the cellular bases of these behavior differences (e.g., alcohol preference, open field activity) using chimeric mice derived from A/J and C57BL6/J, two strains differing markedly in behavior. Studies on a series of these chimeras yielded information about the tissues involved in the A/J vs. BL6/J differences in alcohol preference and open field activity.²,³

To complement the work on chimeras, I created a series of recombinant inbred mouse strains derived from A/J and C57BL6/J (AXB and BXA strains) and used them to attempt a genetic analysis of the same behaviors as I studied in the chimeras.  Recombinant inbred strains offer the capacity to efficiently map single loci,⁴ and they can be used to map the loci contributing to polygenic traits if relatively few loci contribute.⁵ 

My research interest has shifted from mouse to human behavioral variation, and I am in the process of tooling up to work in this area. I am particularly interested in gender, gender differentiated behaviors, and gender identity, and in the relation of these to gender stereotypes. 

      ²Nesbitt, M.N., Spence, M.A. and Butler, K. (1979). Behavior in chimeric mice combining differently behaving strains. Behav. Genet. 9:277-87. 

      ³Nesbitt, M.N., Guthrie, D., Spence, M.A. and Butler, K. (1981). Use of Chimeric Mice to Study Behavior. In: Genetic Strategies in Psychobiology and Psychiatry, Proceedings of the American College of Neuropsychopharmacology. 1979 Meeting. E.S. Gershon et al., editors. Boxwood Press. 

      ⁴Rees D., Nesbitt, M.N., Goldberg, E.H. (1994). Skn 2 is linked to Myb on chromosome 10 of the mouse. Immunogenetics 39:363-6. 

      ⁵Malkinson,A.M., Nesbitt, M.N. and Skamene, E. (1985). Susceptibility to urethan-induced pulmonary adenomas between A/J and C57BL/6J mice: Use of AXB and BXA recombinant inbred lines indicating a three-locus genetic model. JNCI 75:971-974.