Limits...
Effects of body-color mutations on vitality: an attempt to establish easy-to-breed see-through medaka strains by outcrossing.

Ohshima A, Morimura N, Matsumoto C, Hiraga A, Komine R, Kimura T, Naruse K, Fukamachi S - G3 (Bethesda) (2013)

Bottom Line: Fish with the see-through phenotypes were successfully restored in the F2 generation and maintained as closed colonies.We also found that four of the five see-through mutations (b(g8), i-3, gu, and il-1 but not lf) additively decrease viability.Given that heterosis could not overwhelm the viability-reducing effects of the see-through mutations, easy-to-breed see-through strains will only be established by other methods such as conditional gene targeting or screening of new body-color mutations that do not reduce viability.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Evolutionary Genetics, Department of Chemical and Biological Sciences, Japan Women's University, Tokyo.

ABSTRACT
"See-through" strains of medaka are unique tools for experiments: their skin is transparent, and their internal organs can be externally monitored throughout life. However, see-through fish are less vital than normally pigmented wild-type fish, which allows only skilled researchers to make the most of their advantages. Expecting that hybrid vigor (heterosis) would increase the vitality, we outcrossed two see-through strains (SK(2) and STIII) with a genetically distant wild-type strain (HNI). Fish with the see-through phenotypes were successfully restored in the F2 generation and maintained as closed colonies. We verified that genomes of these hybrid see-through strains actually consisted of approximately 50% HNI and approximately 50% SK(2) or STIII alleles, but we could not obtain evidence supporting improved survival of larvae or fecundity of adults, at least under our breeding conditions. We also found that four of the five see-through mutations (b(g8), i-3, gu, and il-1 but not lf) additively decrease viability. Given that heterosis could not overwhelm the viability-reducing effects of the see-through mutations, easy-to-breed see-through strains will only be established by other methods such as conditional gene targeting or screening of new body-color mutations that do not reduce viability.

Show MeSH

Related in: MedlinePlus

Assessment of the STIII mutations on viability. (A) The numbers of backcrossed siblings (obtained by crossing F1 females to STIII males) with various phenotypes at embryonic (light gray) and adult (dark gray and black) stages. Because the il-1 phenotype only appears in adult stages, embryos were classified into eight groups. Adults were classified into 16 groups as shown by dark gray (not accompanied by the il-1 phenotype) and black (accompanied by the il-1 phenotype). (B) All of the 282 adult siblings obtained in panel A were divided into two groups according to either the i-3, lf, gu, or il-1 phenotypes, and the numbers of individuals with wild-type and mutant phenotypes are shown as dark- and light-gray bars, respectively. (C) Body length of the wild-type (dark-gray) and mutant (light-gray) groups classified in panel B. Asterisks indicate significant differences (P < 0.001; Student’s two-tailed t-test). Note the decreased number in i-3, gu, and il-1 (but not lf) siblings (B), and the decreased body length in i-3 and gu (but not lf or il-1) siblings (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
getmorefigures.php?uid=PMC3755918&req=5

fig5: Assessment of the STIII mutations on viability. (A) The numbers of backcrossed siblings (obtained by crossing F1 females to STIII males) with various phenotypes at embryonic (light gray) and adult (dark gray and black) stages. Because the il-1 phenotype only appears in adult stages, embryos were classified into eight groups. Adults were classified into 16 groups as shown by dark gray (not accompanied by the il-1 phenotype) and black (accompanied by the il-1 phenotype). (B) All of the 282 adult siblings obtained in panel A were divided into two groups according to either the i-3, lf, gu, or il-1 phenotypes, and the numbers of individuals with wild-type and mutant phenotypes are shown as dark- and light-gray bars, respectively. (C) Body length of the wild-type (dark-gray) and mutant (light-gray) groups classified in panel B. Asterisks indicate significant differences (P < 0.001; Student’s two-tailed t-test). Note the decreased number in i-3, gu, and il-1 (but not lf) siblings (B), and the decreased body length in i-3 and gu (but not lf or il-1) siblings (C).

Mentions: The i-3, lf, and gu loci of the STIII mutations are independent (Naruse et al. 2000; Fukamachi et al. 2004), but the location of the il-1 locus is unknown. If the il-1 mutation is not linked to any of the other STIII mutations, F2 fish with the STIII phenotype should appear at a frequency of 1/44 (= 1/256). By contrast, if the il-1 mutation is (closely) linked to either of the other STIII mutations, such F2 should be obtained at a higher frequency. Among the 8,011 F2 eggs that we collected, 7,723 (96.4%) embryos developed normally, 94 of which exhibited the i-3-lf-gu triple recessive phenotype (the il-1 phenotype does not appear at this stage). Interestingly, this count was close to, but significantly lower than, the expected value (7,723 × 1/64 = 120.7; P = 0.014, χ2 test). The reason is unclear, but one or a combination of the STIII mutations may slightly inhibit normal development of embryos, which could statistically be detected only when thousands are examined (note that such an effect was not detected in Figure 5A, where only 773 embryos were examined). We selectively raised these triple recessive F2 larvae, obtained 34 adult fish, and found only two males and two females with the STIII (i-3-lf-gu-il-1 quadruple recessive) phenotype. This count (i.e., four) was also significantly lower than the expected value (34 × 1/4 = 8.5; P = 0.017, χ2 test), which most likely reflects the viability-reducing effect of the il-1 mutation (described later; see Figure 5). This low count of the quadruple recessive F2s also indicates that the il-1 locus is not closely linked to the i-3, lf, or gu loci.


Effects of body-color mutations on vitality: an attempt to establish easy-to-breed see-through medaka strains by outcrossing.

Ohshima A, Morimura N, Matsumoto C, Hiraga A, Komine R, Kimura T, Naruse K, Fukamachi S - G3 (Bethesda) (2013)

Assessment of the STIII mutations on viability. (A) The numbers of backcrossed siblings (obtained by crossing F1 females to STIII males) with various phenotypes at embryonic (light gray) and adult (dark gray and black) stages. Because the il-1 phenotype only appears in adult stages, embryos were classified into eight groups. Adults were classified into 16 groups as shown by dark gray (not accompanied by the il-1 phenotype) and black (accompanied by the il-1 phenotype). (B) All of the 282 adult siblings obtained in panel A were divided into two groups according to either the i-3, lf, gu, or il-1 phenotypes, and the numbers of individuals with wild-type and mutant phenotypes are shown as dark- and light-gray bars, respectively. (C) Body length of the wild-type (dark-gray) and mutant (light-gray) groups classified in panel B. Asterisks indicate significant differences (P < 0.001; Student’s two-tailed t-test). Note the decreased number in i-3, gu, and il-1 (but not lf) siblings (B), and the decreased body length in i-3 and gu (but not lf or il-1) siblings (C).
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC3755918&req=5

fig5: Assessment of the STIII mutations on viability. (A) The numbers of backcrossed siblings (obtained by crossing F1 females to STIII males) with various phenotypes at embryonic (light gray) and adult (dark gray and black) stages. Because the il-1 phenotype only appears in adult stages, embryos were classified into eight groups. Adults were classified into 16 groups as shown by dark gray (not accompanied by the il-1 phenotype) and black (accompanied by the il-1 phenotype). (B) All of the 282 adult siblings obtained in panel A were divided into two groups according to either the i-3, lf, gu, or il-1 phenotypes, and the numbers of individuals with wild-type and mutant phenotypes are shown as dark- and light-gray bars, respectively. (C) Body length of the wild-type (dark-gray) and mutant (light-gray) groups classified in panel B. Asterisks indicate significant differences (P < 0.001; Student’s two-tailed t-test). Note the decreased number in i-3, gu, and il-1 (but not lf) siblings (B), and the decreased body length in i-3 and gu (but not lf or il-1) siblings (C).
Mentions: The i-3, lf, and gu loci of the STIII mutations are independent (Naruse et al. 2000; Fukamachi et al. 2004), but the location of the il-1 locus is unknown. If the il-1 mutation is not linked to any of the other STIII mutations, F2 fish with the STIII phenotype should appear at a frequency of 1/44 (= 1/256). By contrast, if the il-1 mutation is (closely) linked to either of the other STIII mutations, such F2 should be obtained at a higher frequency. Among the 8,011 F2 eggs that we collected, 7,723 (96.4%) embryos developed normally, 94 of which exhibited the i-3-lf-gu triple recessive phenotype (the il-1 phenotype does not appear at this stage). Interestingly, this count was close to, but significantly lower than, the expected value (7,723 × 1/64 = 120.7; P = 0.014, χ2 test). The reason is unclear, but one or a combination of the STIII mutations may slightly inhibit normal development of embryos, which could statistically be detected only when thousands are examined (note that such an effect was not detected in Figure 5A, where only 773 embryos were examined). We selectively raised these triple recessive F2 larvae, obtained 34 adult fish, and found only two males and two females with the STIII (i-3-lf-gu-il-1 quadruple recessive) phenotype. This count (i.e., four) was also significantly lower than the expected value (34 × 1/4 = 8.5; P = 0.017, χ2 test), which most likely reflects the viability-reducing effect of the il-1 mutation (described later; see Figure 5). This low count of the quadruple recessive F2s also indicates that the il-1 locus is not closely linked to the i-3, lf, or gu loci.

Bottom Line: Fish with the see-through phenotypes were successfully restored in the F2 generation and maintained as closed colonies.We also found that four of the five see-through mutations (b(g8), i-3, gu, and il-1 but not lf) additively decrease viability.Given that heterosis could not overwhelm the viability-reducing effects of the see-through mutations, easy-to-breed see-through strains will only be established by other methods such as conditional gene targeting or screening of new body-color mutations that do not reduce viability.

View Article: PubMed Central - PubMed

Affiliation: Laboratory of Evolutionary Genetics, Department of Chemical and Biological Sciences, Japan Women's University, Tokyo.

ABSTRACT
"See-through" strains of medaka are unique tools for experiments: their skin is transparent, and their internal organs can be externally monitored throughout life. However, see-through fish are less vital than normally pigmented wild-type fish, which allows only skilled researchers to make the most of their advantages. Expecting that hybrid vigor (heterosis) would increase the vitality, we outcrossed two see-through strains (SK(2) and STIII) with a genetically distant wild-type strain (HNI). Fish with the see-through phenotypes were successfully restored in the F2 generation and maintained as closed colonies. We verified that genomes of these hybrid see-through strains actually consisted of approximately 50% HNI and approximately 50% SK(2) or STIII alleles, but we could not obtain evidence supporting improved survival of larvae or fecundity of adults, at least under our breeding conditions. We also found that four of the five see-through mutations (b(g8), i-3, gu, and il-1 but not lf) additively decrease viability. Given that heterosis could not overwhelm the viability-reducing effects of the see-through mutations, easy-to-breed see-through strains will only be established by other methods such as conditional gene targeting or screening of new body-color mutations that do not reduce viability.

Show MeSH
Related in: MedlinePlus