| First Author | Gerritsen JA | Year | 1992 |
| Journal | Mouse Genome | Volume | 90 |
| Issue | 1 | Pages | 90-91 |
| Mgi Jnum | J:35 | Mgi Id | MGI:48576 |
| Citation | Gerritsen JA, et al. (1992) The SWV and C57BL/6 inbred strains exhibit the same difference in lateralization of handedness as the selected LO and HI lines. Mouse Genome 90(1):90-91 |
| abstractText | Full text of Mouse Genome contribution: THE SWV AND C57BL/6 INBRED STRAINS EXHIBIT THE SAME DIFFERENCE IN LATERALIZATION OF HANDEDNESS AS THE SELECTED LO AND HI LINES. JA. Gerritsen and F.G. Biddle*; Departments of Paediatrics and Medical Biochemistry, University of Calgary, Calgary, Alberta, Canada T2N 4N1 (*For correspondence) Introduction. The direction of handedness in the mouse can be measured by a left and right paw reaching task in an unbiased test chamber and direction does not appear to be a genetically determined variable (1). Within tested strains, equal numbers of mice are left and right handed and, therefore, each mouse is lateralized left or right. Within C57BL/6, hand usage is a symmetrical U-shaped distribution and the direction of hand usage does not respond to selection (2). The strength or degree of lateralization of hand usage is a genetic variable because a bidirectional selection study, starting with a constructed heterogenous population, produced both HI (highly lateralized) and LO (weakly lateralized) lines within a relatively few generations (3). The HI line is similar in strength of lateralization to C57BL/6 but the phenotype of LO line has not been reported among inbred strains. Recently, a brief note suggested the I/Ln strain is "ambidextrous" (4). We report here that handedness of the SWV inbred strain is as weakly lateralized as the selected LO line and compare it with the highly lateralized C57BL/6 strain. Materials and Methods. The SWV/Bid and C57BL/6JBid are registered inbred strains (5) and are maintained by continued sister-brother inbreeding. Currently, SWV is at the F103 generation and C57BL/6 is at the +F49 generation after being received from the Jackson Laboratory in 1979. Adult female and male mice were fasted 24-48 hours and assessed for hand usage in an unbiased testing chamber by previously described methods (3,6). Fifty paw reaches were recorded for each mouse and the number (0 to 50) of right paw entries (RPE) was used as one measure of handedness. Left-handed mice have RPE's of 0-24; right-handed mice have RPE's of 26-50; a mouse with 25 RPE would be defined as ambilateral. The strength or degree of lateralization of paw preference was measured by the "preferred paw entry" score (PPE) that is a non-monotonic transformation of the RPE score (PPE = absolute | RPE-25 | +25). The PPE score has values from 25 to 50 and is a measure of the strength of lateralization without regard to its left or right direction. Comparisons between PPE scores were made with the logit-transformed PPE values (3). Comparisons among frequencies were made with the G-test (7). The level of significance for all comparisons was alpha <= 0.05. Results and Discussion. The RPE scores for C57BL/6 (30 females, 15 males) and SWV (30 females, 10 males) are compared in Figure 1. The distribution of RPE scores of C57BL/6 is U shaped and was expected but the distribution of RPE of SWV is distinctly unimodal and was not expected. The direction of handedness was assessed using the RPE scores Table 1. The RPE's were grouped as left (0-24) or right (26-50); mice with an RPE of 25 were excluded from analysis. In the present sample, there are no significant differences in the numbers of left- and right-handed mice either between females and males within the two strains or between the two strains when tested by a G-test against the hypothesis of equal frequency. The asymmetry of handedness was assessed in two ways. First, the RPE scores were divided into three equal classes (Table 2) and there is a significant difference in the distributions between the two strains (Ghet = 10.79, 2 d.f., P < 0.005). SWV is less lateralized than C57BL/6 (Fig. 1). Second, the preferred paw entry (PPE) scores were plotted as a histogram (Fig. 2) and summarized in Table 3. The difference in the mean logit-transformed PPE (or LPPE) between C57BL/6 and SWV is significant because there is no overlap between their 95% confidence limits. The PPE equivalent to the mean LPPE is indicated in Table 3. C57BL/6 and SWV have equal frequencies of left- and right-handed individuals and are similar to other strains that have been assessed in an unbiased test (1). Our C57BL/6 is highly lateralized and is similar to other reports of C57BL/6 and the HI line that was selected for high lateralization of paw preference (mean PPE = 44; ref. 3). In contrast to these results, SWV is weakly lateralized or possibly ambilateral (Fig. 2). With a median PPE of 34, SWV may have a phenotype that is similar to or even more weakly lateralized than the LO line that was selected for low lateralization of paw preference (mean PPE = 37; ref. 3). If the "low lateralization" phenotype is found among common inbred strains such as SWV, it will be important to determine whether it is genetically similar to the selected LO line by complementation test. The difference in degree of lateralization, measured by PPE between the SWV and C57BL/6 inbred strains, appears to be as large or larger than the reported difference between the LO and HI lines that were selected from a genetically heterogeneous stock (3). If the low and high lateralization characteristics are found as discrete phenotypes among the common inbred strains, it is possible that only a few major genetic factors control this quantitative trait. We suggest this is strong impetus for a directed genetic survey of this trait among selected inbred strains of the mouse. Acknowledgements. J.A.G. was supported by an A.H.F.M.R. Summer Studentship and F.G.B. is supported by the Alberta Children's Hospital Foundation. The laboratory is supported by grants to F.G.B. from the Medical Research Council of Canada. References 1. Collins, R.L. (1968) J. Hered., 59: 9-12. 2. Collins, R.L. (1969) J. Hered., 60: 117-119. 3. Collins, R.L. (1985) In: Cerebral Lateralization in Nonhuman Species. S.D. Glick, ed. Academic Press, Orlando, pp. 41-71. 4. Lipp, H.-P. and Waanders, R. (1990) Behav. Genet., 20: 728-729 (abstract). 5. Lyon, M.F. and Searle, A.G., eds (1989) Genetic Variants and Strains of the Laboratory Mouse. Second edition. Oxford University Press, Oxford. 6. Collins, R.L. (1975) Science, 187: 181-184. 7. Sokal, R.R. and FJ. Rohlf (1969) Biometry. Freeman, San Francisco. |
