Two genetic loci control syllable sequences of ultrasonic courtship vocalizations in inbred mice

Abstract

Background: The ultrasonic vocalizations (USV) of courting male mice are known to possess a phonetic structure with a complex combination of several syllables. The genetic mechanisms underlying the syllable sequence organization were investigated.

Results: This study compared syllable sequence organization in two inbred strains of mice, 129S4/SvJae (129) and C57BL6J (B6), and demonstrated that they possessed two mutually exclusive phenotypes. The 129S4/SvJae (129) strain frequently exhibited a "chevron-wave" USV pattern, which was characterized by the repetition of chevron-type syllables. The C57BL/6J strain produced a "staccato" USV pattern, which was characterized by the repetition of short-type syllables. An F1 strain obtained by crossing the 129S4/SvJae and C57BL/6J strains produced only the staccato phenotype. The chevron-wave and staccato phenotypes reappeared in the F2 generations, following the Mendelian law of independent assortment.

Conclusions: These results suggest that two genetic loci control the organization of syllable sequences. These loci were occupied by the staccato and chevron-wave alleles in the B6 and 129 mouse strains, respectively. Recombination of these alleles might lead to the diversity of USV patterns produced by mice.

Figure 1

Syllabic composition of the USVs of 129, B6, and F1 mice. (a) up: staccato (short repeats) (red) and chevron-wave (chevron repeats) (blue) of 129 (left), B6 (center), and F1 (right). The box represents short or chevron adjacently repeated regions. down: detailed view of the area in the triangle. (b) The ratio of each syllable type. 129 and B6 exhibited different use of short and chevron. F1 had a similar syllable composition to B6, but differed from 129. down: representative sonogram for each syllable produced by 129. * p < 0.01. (c) Sniffing and total number of syllables during sniffing. * p < 0.05.

Figure 2

Syllable composition of B6 and 129 males was not affected by the female strain. (a) The ratio of each syllable type for 129 and B6 male mice stimulated by a 129 female. The syllable composition pattern was consistent with Fig. 1 (stimulated by B6 female). (b) Time spent sniffing (left) and total number of syllables (right) during sniffing behavior. B6 and 129 males stimulated by 129 female. * p < 0.01.

Figure 3

Sequential syllable structure for USVs of B6, 129, and F1 mice. (a) Syllable repetition in B6, 129, and F1 mice. The number of events of differing length was normalized with the total number of syllables. B6 and 129 mice emitted different amounts of short repetitions and chevron repetitions. B6-like phenotypes were dominant. * p < 0.01. (b) Proportions of animals with syllable repeats containing at three to six syllables.

Figure 4

F2 USVs were diversified into B6-like, 129-like, and mixed phenotypes. (a) USV patterns of F2 mice. Representative sonograms of the four types of F2 mice are shown. Chevron repeat (red) and short repeats (blue) are highlighted (box). (b) Proportions of short (x-axis) and chevron (y-axis) for each mouse are shown. One dot is one mouse. Short and chevron compositions for B6 (blue) and F1 (green) overlapped, whereas 129 USVs (red) were discrete. F2 (black) mice were B6-like and 129-like, containing both chevron and short rich repeats, while others lacked chevrons and short syllables. (c) The ratio of F2 mice with syllable repeats greater than four. Chevron-rich USVs were recessive, whereas short-rich USVs were dominant.