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Expression of the lactate dehydrogenase genes of Xenopus species and interspecies hybrids during early development
Comp. Biochem. PhysioL Vol. 76B, No. 1, pp. 17 to 21, 1983 Printed in Great Britain
0305-0491/83$3.00+0.00 (C 1983PergamonPress Ltd
EXPRESSION OF THE LACTATE D E H Y D R O G E N A S E GENES OF XENOPUS SPECIES A N D INTERSPECIES HYBRIDS D U R I N G EARLY DEVELOPMENT E. VONWYL Station de Zoologie Exp~rimentale, Universit6 de Gen~ve, 154 Route de Malagnou, CH-1224 Ch~neBougeries/Geneva, Switzerland (Received 15 February" 1983)
Abstraet--1. The expression of LDH genes throughout early development of different Xenopus species, and interspecies hybrids has been compared. 2. In X. 1. victorianus oocytes the LDH-B4 polymer is synthesizedexclusivelyand is stored during early embryonic stages. For the first time at stage 27 is the embryonic LDH gene activity manifest. 3. In other species the situation is somewhat more complicated, in that additional anodal bands appear or, like in X. clivii, even cathodal polymers are formed. 4. In X. 1. vietorianus ~. x X. borealis ~ hybrids only the maternal pattern was expressed throughout the whole embryonic development. This allelic repression persisted up to metamorphosis.
INTRODUCTION
natant stored at -20°C. The samples were used for electrophoresis within a few days.
Lactate dehydrogenase (LDH) is a tetrameric enzyme composed of the two subunits A and B. Five isozymes result by random combination of the subunits (Appella and Markert, 1961; Markert, 1963). LDH is a relatively well known isozyme system in Xenopus (Kunz and Hearn, 1967; Claycomb and Villee, 1971; Kunz, 1973; Wall and Blackler, 1974; Faulhaber and Lyra, 1975a,b; Vonwyl and Fischberg, 1980a,b; Vonwyl, 1982, 1983). In X. 1. laevis 4 molecular forms exist in oocytes and persist up to the tail bud stage (Kunz and Hearn, 1967: Ciaycomb and Villee, 1971; Kunz, 1973; Faulhaber and Lyra 1975a). When myotomes begin to function (stages 25-27) a cathodal isozyme appears. In X.I. laevis × X. borealis (misidentified as muelleri; see Brown et aL, 1977) hybrids the LDH isozyme pattern of early embryos resembles that of the maternal parent (Wall and Blackler, 1974). In later stages both parents contribute to the isozyme phenotype (Wall and Blackler, 1974; Vonwyl and Fischberg, 1980b). In the present work the research was extended to other species. It was especially focused on Xenopus l. victorianus in which all LDH bands can clearly be identified. In addition a suitable hybrid combination was studied.
Polyacrylamide gel electrophoresis The isozymes were separated using the disc system of Ornstein (1964) and Davis (1964). Separation was done in long cylindrical gels (separation gel 15 cm). The resolution of this method was found to be superior to the slab gel method. Electrophoresis was carried out with a current of 1 mA/gel for 30 min followed by 4 mA/gel for about 5 hr. LDH staining Isozymes were visualized by incubating the gels at 37°C in the dark for about 30rain in the staining solution described by Dietz and Lubrano (1967) slightly modified. Determination of protein concentration The method of Lowry et al. (1951) was used. However, the more stable sodium citrate was substituted for sodium potassium tartrate (Eggstein and Kreutz, 1955).
RESULTS
The LDH isozyme pattern in early development of X. 1. victorianus is shown in Fig. 1. In oocytes and in early embryonic stages only the B4 polymer can be seen. At stage 27 gene activity is seen for the first time in embryogenesis. It appears as the A4 polymer followed by the A3B and A2B2 polymers. Thus, the gene which codes for the A subunit is first active followed by the gene which codes for the B subunit. Furthermore, from the fact that the A~B polymer follows the appearance of the A4 isozyme, it can be concluded that the B4 isozyme must be stocked in early embryonic stages and is not continuously synthesized. If B subunits were continuously synthesized then the AB 3 polymer should precede the appearance of the A2B2 polymer etc. In X. borealis there are additional anodal isozymes found in early embryonic stages (Fig. 1).
MATERIALS AND METHODS
Animals Embryos and tadpoles were staged according to Nieuwkoop and Faber (1956). The hybrids were all produced by natural fertilization. Extract preparation Seven to ten embryos or eggs were homogenized in a glass microhomogenizer filled with 0.1 M Tris-HC1 pH 7.4 buffer containing 0.25 M sucrose. The samples were centrifuged at 30,000g for 30min in a Sorvall centrifuge and the super-
CBP(B)76/1 S
17
18
E. VONWYL
A4
A4
A3B
A2B2
B.
stages >
stages
o 12 27 29 35/640 45 48
12 27 29 35/6 40 45
® Fig. 1. LDH gene activity in embryonic development of X. 1. victorianus and X. borealis.
In hybrids from the combination X. 1. victorianus x X. borealis ~ there are only the maternal isozymes expressed in early development (Fig. 2). At stage 27 the A4 polymer which has the same mobility in both parents can be seen. Up to stage 66 (end of metamorphosis) there is no indication that a X. borealis polymer containing B subunits is synthesized. Beginning stage 66 organs with X. borealis, LDH polymers containing B subunits can be found (Fig. 3). One exception was also observed in which, at stage 66, still no borealis polymer containing B subunits was synthesized. Thus allelic repression continuous at least up to metamorphosis. While the A subunit is the same for X. 1. victorianus and X. borealis, A4 subbands occur only in X. borealis (Vonwyl and Fischberg, 1980a). At stage 66 for the first time in embryogenesis a typical borealis A 4 subband can be seen in these hybrids (Fig. 2, arrow). X.I. bunyoniensis x X. ruwenzoriensis and X.I. laevis x clivii hybrids were also investigated (not
shown). Unfortunately. the isozyme patterns are difficult to interpret. The only conclusion which can be drawn is that the isozyme patterns of the early embryonic stages are those of the maternal parents. While X.I. victorianus, X.I. bunyoniensis, X. 1. laevis, X. borealis, X. tropicalis and X. ruwenzoriensis (most patterns not shown) exhibits anodal bands in oocytes and early embryonic stages, X. clivii do not behave in the same way (Fig. 4). In these species all 5 isozymes are expressed and the most cathodal isozymes are quantitatively more pronounced. DISCUSSION
X. 1. victorianus was choosen to investigate since all isozyme bands of this species are clearly defined (Vonwyl and Fischberg, 1980a). It could be concluded that the B4 homopolymer is synthesized in oocytes and stored in early development. It must be noted that it is the isozyme B4 itself which is stored.
LDH in developing Xenopus hybrids However, we can not exclude that its messenger RNA is also stored, but one would have to assume that it is not translated in early stages. The situation in other species, mostly with more than 5 isozymes, is less clear. Generally, they are characterized by the appearance of anodal bands in oocytes and early embryonic stages. This is, for example, true for X. 1. laevis (Kunz and Hearn, 1969; Claycomb and Villee, 1971; Kunz, 1973; Wall and Blackler, 1974; Faulhaber and Lyra, 1975a,b). One exception must be noted, namely X. clivii, in which cathodal isozymes are mainly expressed. In hybrids the maternal pattern was found in early embryonic stages. This is in agreement with the results of Wall and Blackler (1974). This phenomenon can be easly explained by the fact that LDH molecules are synthesized in oocytes and stored in early embryonic stages. In X. 1. victorianus ~ × X. borealis ~ hybrids tern-
19
porary allelic repression of synthesis of LDH isozymes of one species has been observed. It is known that allelic repression is at least temporary, is partially or complete and occurs mainly in early embryonic development (Castro-Sierra and Ohno, 1968; Hitzeroth et aL, 1968; Klose et al., 1969; Goldberg et al., 1969; Klose and Wolf, 1970; Pipkin and Bremner, 1970; Schwartz, 1971; Chao and Scandalios, 197l; Whitt et al., 1973; Herrera, 1979; Invanenkov, 1980). In adult Xenopus no such repression of isozymes or structural proteins has as yet been found. From two dimensional gel electrophoresis studies De Robertis and Black (1979) concluded that in X. laevis × X. borealis adult hybrids the protein coding genes of both parents are expressed. The same finding has been reported for LDH (Wall and Blackler, 1974; Vonwyl and Fischberg, 1980b). Recently, a study of hemoglobin of interspecies hybrids (Bfirki, in preparation) came to the same conclusion.
A4
A3B
A2B 2
stages
stag~
12 27 29 35/6 40 45 48 50 52' 58 66
12 27, 45
w
Fig. 2. LDH gene activity in embryonic development of the two hybrids X. 1. victorianus 2 x X. borealis d (A) and X. borealis 9 x X.I. victorianus ~ (B).
E. VONWYL
2O
A4
A4
A3B
A3B
A2B2
A2B2 AB3 B4
"O
== O. X
c
=* eel i
t::¢O tD +~. . . . .
O
¢3 ~
J~
stages
® Fig. 3. LDH isozyme patterns of X.I. victorianus, X. borealis and their hybrid combination (X. 1. victorianus ~2 × X. borealis ~) at stage 66 (adult frogs). The two organs liver and kidney have been analyzed.
Acknowledgements--The author wishes to thank Professor Dr M. Fischberg for facilities and Dr E. Biirki for critically reading the manuscript. This study has been supported by the Georges and Antoine Claraz Foundation and the Fonds National Suisse de la Recherche Scientifique.
REFERENCES
Appella E. and Markert C. L. (1961) Dissociation of lactate dehydrogenase into subunits with guanidine hydrochlordie. Biochem. biophys. Res. Commun. 6, 171-176. Brown D. D., Dawid J. B. and Reeder R. H. (1977) Xenopus borealis misidentified as Xenopus muelleri. Devl Biol. 59, 266-267. Castro-Sierra E. and Ohno S. (1968) Allelic inhibition at the autosomally inherited gene locus for liver alcohol dehydrogenase in chicken-qualine hybrids. Bioehem. Genet. 1, 323-335. Chao S. E. and Scandalios J. G. (1971) Alpha-amylase of
Fig. 4. LDH gene activity in embryonic development of X. clivii.
maize: Differential allelic expression at the amyl-I gene locus, and some physicochemical properties of the isozymes. Genetics 69, 47-61. Claycomb W. C. and Villee C. A. (1971) Lactate dehydrogenase isozymes of Xenopus laevis: Factors affecting their appearance during early development. Devl Biol. 24, 413-427. Davis B. J. (1964) Disc electrophoresis. II. Method and application to human serum proteins. Ann. N.Y. Acad. Sci. 121, 40~427. De Robertis E. M. and Black P. (1979) Hybrids of Xenopus laevis and Xenopus borealis expressed proteins from both parents. Devl Biol. 68, 334~339. Dietz A. A. and Lubrano T. (1967) Separation and quantitation of lactic dehydrogenase isoenzymes by disc electrophoresis. Analyt. Biochem. 20, 246-257. Eggstein M. and Kreutz F. H. (1955) Vergleichende Untersuchungen zur quantitativen Eiweissbestimmung im Liquor und eiweissarmen L6sungen, Klin. Wsehr. 33, 879-884.
LDH in developing Xenopus hybrids Faulhaber I. and Lyra L. (1975a) Ver~inderungen der Aktivit~t und des Isoenzymmusters der LDH (Laktatdehydrogenase) w~ihrend der Entwicklung bei Urodelen und Anuren (Triturus alpestris und vulgaris, Ambystoma mexicanum, Xenopus laevis). Wilhelm Roux Arch. 176, 191-205.
Faulhaber I. and Lyra L. (1975b) Aktivit~it und Isoenzyme der Laktatdehydrogenase in Organen von Amphibien (Xenopus laevis, Ambystoma mexicanum, Triturus alpestris und vulgaris) und der Effekt von Gonadotropin- injektionen auf das Enzym im Fettk6rper des miinnlichen Krallenfosches. Hoppe-Seyler's Z. physiol. Chem. 356, 1277-1281. Goldberg E., Cuerrier J. P. and Ward J. C. (1969) Lactate dehydrogenase ontogeny, paternal gene activation, and tetramer assembly in embryos of brook trout, lake trout, and their hybrids. Biochem. Genet. 2, 335-350. Herrera R. J. (1979) Preferential gene expression of an amylase allele in interspecific hybrids of Xiphophorus. Biochem. Genet. 17, 223-227. Hitzeroth H., Klose J., Ohno S. and Wolf U. (1968) Asynchronous activation of parental alleles at the tissuespecific gene loci observed on hybrid trout during early development. Biochem. Genet. 1, 287-300. Ivanenkov V. V. (1980) Differential expression of allelic carboxylesterase-2 genes in oocytes of loach (Misgurnus fossilis) and heterogeneity of loach oocytes and eggs for the expression of allelic carboxylesterase-2 genes. Biochem. Genet. 18, 365-375. Klose J. and Wolf U. (1970) Transitional hemizygosity of the maternally derived allele at the 6PGD locus during early development of the cyprinid fish Rutilus rutilus. Biochem. Genet. 14, 87-92. Klose J., Hitzeroth H., Ritter H., Schmidt E. and Wolf U. (1969) Persistence of maternal isoenzyme patterns of the lactate dehydrogenase and phosphoglucomutase system during early development of hybrid trout. Biochem. Genet. 3, 91-97. Kunz Y. W. (1973) Changes in lactate dehydrogenase
21
isozyme pattern during the development of Xenopus laevis (Daudin). Rev. suisse Zool. 80, 431-446. Kunz Y. W. and Hearn J. (1967) Heterogeneity of lactate dehydrogenase in the developing and adult Xenopus laevis. Experientia 23, 683-686. Lowry O. H.,, Rosebrough N. J., Farr A. L. and Randall R. J. (1951) Protein measurement with the folin phenol reagent. J. biol. Chem. 193, 265-275. Markert C. L. (1963) Lactate dehydrogenase isozymes: Dissociation and recombination of subunits. Science, N.Y. 140, 1329-1330. Nieuwkoop P. D. and Faber J. (1965) Normal Table of Xenopus laevis. North-Holland, Amsterdam. Ornstein L. (1964) Disc electrophoresis. I. Background and theory. Ann. N.Y. Acad. Sci. 121, 321-403. Pipkin S. B. and Bremner T. A. (1970) Aberrant octanol dehydrogenase isozyme patterns in interspecific Drosophila hybrids. J. exp. Zool. 175, 283-296. Schwartz D. (1971) Genetic control of alcohol dehydrogenase a competition model for regulation of gene action. Genetics 67, 411-425. Vonwyl E. (1982) Lactate dehydrogenase isozymes of two new Xenopus species. Experientia 38, 1205-1207. Vonwyl E. (1983) Lactate dehydrogenase isozymes in the genus Xenopus: Analyses of complex isozyme patterns. Comp. Biochem. Physiol. 74B, 725-733. Vonwyl E. and Fischberg M. (1980a) Lactate dehydrogenase isozymes in the genus Xenopus: Species-specific patterns. J. exp. Zool. 211, 281-290. Vonwyl E. and Fischberg M. (1980b) Expression of the lactate dehydrogenase genes in Xenopus species hybrids. DeL,I Biol. 75, 505-508. Wall D. A. and Blackler A. W. (1974) Expression of lactate dehydrogenase phenotypes in intraspecific and interspecific matings of two species of Xenopus. Devl Biol. 41, 79-109. Whitt G. S., Childers W. F. and Cho P. L. (1973) Alletic expression at enzyme loci in an intertribal hybrid sunfish. J. Hered. 64, 55-61.
0305-0491/83$3.00+0.00 (C 1983PergamonPress Ltd
EXPRESSION OF THE LACTATE D E H Y D R O G E N A S E GENES OF XENOPUS SPECIES A N D INTERSPECIES HYBRIDS D U R I N G EARLY DEVELOPMENT E. VONWYL Station de Zoologie Exp~rimentale, Universit6 de Gen~ve, 154 Route de Malagnou, CH-1224 Ch~neBougeries/Geneva, Switzerland (Received 15 February" 1983)
Abstraet--1. The expression of LDH genes throughout early development of different Xenopus species, and interspecies hybrids has been compared. 2. In X. 1. victorianus oocytes the LDH-B4 polymer is synthesizedexclusivelyand is stored during early embryonic stages. For the first time at stage 27 is the embryonic LDH gene activity manifest. 3. In other species the situation is somewhat more complicated, in that additional anodal bands appear or, like in X. clivii, even cathodal polymers are formed. 4. In X. 1. vietorianus ~. x X. borealis ~ hybrids only the maternal pattern was expressed throughout the whole embryonic development. This allelic repression persisted up to metamorphosis.
INTRODUCTION
natant stored at -20°C. The samples were used for electrophoresis within a few days.
Lactate dehydrogenase (LDH) is a tetrameric enzyme composed of the two subunits A and B. Five isozymes result by random combination of the subunits (Appella and Markert, 1961; Markert, 1963). LDH is a relatively well known isozyme system in Xenopus (Kunz and Hearn, 1967; Claycomb and Villee, 1971; Kunz, 1973; Wall and Blackler, 1974; Faulhaber and Lyra, 1975a,b; Vonwyl and Fischberg, 1980a,b; Vonwyl, 1982, 1983). In X. 1. laevis 4 molecular forms exist in oocytes and persist up to the tail bud stage (Kunz and Hearn, 1967: Ciaycomb and Villee, 1971; Kunz, 1973; Faulhaber and Lyra 1975a). When myotomes begin to function (stages 25-27) a cathodal isozyme appears. In X.I. laevis × X. borealis (misidentified as muelleri; see Brown et aL, 1977) hybrids the LDH isozyme pattern of early embryos resembles that of the maternal parent (Wall and Blackler, 1974). In later stages both parents contribute to the isozyme phenotype (Wall and Blackler, 1974; Vonwyl and Fischberg, 1980b). In the present work the research was extended to other species. It was especially focused on Xenopus l. victorianus in which all LDH bands can clearly be identified. In addition a suitable hybrid combination was studied.
Polyacrylamide gel electrophoresis The isozymes were separated using the disc system of Ornstein (1964) and Davis (1964). Separation was done in long cylindrical gels (separation gel 15 cm). The resolution of this method was found to be superior to the slab gel method. Electrophoresis was carried out with a current of 1 mA/gel for 30 min followed by 4 mA/gel for about 5 hr. LDH staining Isozymes were visualized by incubating the gels at 37°C in the dark for about 30rain in the staining solution described by Dietz and Lubrano (1967) slightly modified. Determination of protein concentration The method of Lowry et al. (1951) was used. However, the more stable sodium citrate was substituted for sodium potassium tartrate (Eggstein and Kreutz, 1955).
RESULTS
The LDH isozyme pattern in early development of X. 1. victorianus is shown in Fig. 1. In oocytes and in early embryonic stages only the B4 polymer can be seen. At stage 27 gene activity is seen for the first time in embryogenesis. It appears as the A4 polymer followed by the A3B and A2B2 polymers. Thus, the gene which codes for the A subunit is first active followed by the gene which codes for the B subunit. Furthermore, from the fact that the A~B polymer follows the appearance of the A4 isozyme, it can be concluded that the B4 isozyme must be stocked in early embryonic stages and is not continuously synthesized. If B subunits were continuously synthesized then the AB 3 polymer should precede the appearance of the A2B2 polymer etc. In X. borealis there are additional anodal isozymes found in early embryonic stages (Fig. 1).
MATERIALS AND METHODS
Animals Embryos and tadpoles were staged according to Nieuwkoop and Faber (1956). The hybrids were all produced by natural fertilization. Extract preparation Seven to ten embryos or eggs were homogenized in a glass microhomogenizer filled with 0.1 M Tris-HC1 pH 7.4 buffer containing 0.25 M sucrose. The samples were centrifuged at 30,000g for 30min in a Sorvall centrifuge and the super-
CBP(B)76/1 S
17
18
E. VONWYL
A4
A4
A3B
A2B2
B.
stages >
stages
o 12 27 29 35/640 45 48
12 27 29 35/6 40 45
® Fig. 1. LDH gene activity in embryonic development of X. 1. victorianus and X. borealis.
In hybrids from the combination X. 1. victorianus x X. borealis ~ there are only the maternal isozymes expressed in early development (Fig. 2). At stage 27 the A4 polymer which has the same mobility in both parents can be seen. Up to stage 66 (end of metamorphosis) there is no indication that a X. borealis polymer containing B subunits is synthesized. Beginning stage 66 organs with X. borealis, LDH polymers containing B subunits can be found (Fig. 3). One exception was also observed in which, at stage 66, still no borealis polymer containing B subunits was synthesized. Thus allelic repression continuous at least up to metamorphosis. While the A subunit is the same for X. 1. victorianus and X. borealis, A4 subbands occur only in X. borealis (Vonwyl and Fischberg, 1980a). At stage 66 for the first time in embryogenesis a typical borealis A 4 subband can be seen in these hybrids (Fig. 2, arrow). X.I. bunyoniensis x X. ruwenzoriensis and X.I. laevis x clivii hybrids were also investigated (not
shown). Unfortunately. the isozyme patterns are difficult to interpret. The only conclusion which can be drawn is that the isozyme patterns of the early embryonic stages are those of the maternal parents. While X.I. victorianus, X.I. bunyoniensis, X. 1. laevis, X. borealis, X. tropicalis and X. ruwenzoriensis (most patterns not shown) exhibits anodal bands in oocytes and early embryonic stages, X. clivii do not behave in the same way (Fig. 4). In these species all 5 isozymes are expressed and the most cathodal isozymes are quantitatively more pronounced. DISCUSSION
X. 1. victorianus was choosen to investigate since all isozyme bands of this species are clearly defined (Vonwyl and Fischberg, 1980a). It could be concluded that the B4 homopolymer is synthesized in oocytes and stored in early development. It must be noted that it is the isozyme B4 itself which is stored.
LDH in developing Xenopus hybrids However, we can not exclude that its messenger RNA is also stored, but one would have to assume that it is not translated in early stages. The situation in other species, mostly with more than 5 isozymes, is less clear. Generally, they are characterized by the appearance of anodal bands in oocytes and early embryonic stages. This is, for example, true for X. 1. laevis (Kunz and Hearn, 1969; Claycomb and Villee, 1971; Kunz, 1973; Wall and Blackler, 1974; Faulhaber and Lyra, 1975a,b). One exception must be noted, namely X. clivii, in which cathodal isozymes are mainly expressed. In hybrids the maternal pattern was found in early embryonic stages. This is in agreement with the results of Wall and Blackler (1974). This phenomenon can be easly explained by the fact that LDH molecules are synthesized in oocytes and stored in early embryonic stages. In X. 1. victorianus ~ × X. borealis ~ hybrids tern-
19
porary allelic repression of synthesis of LDH isozymes of one species has been observed. It is known that allelic repression is at least temporary, is partially or complete and occurs mainly in early embryonic development (Castro-Sierra and Ohno, 1968; Hitzeroth et aL, 1968; Klose et al., 1969; Goldberg et al., 1969; Klose and Wolf, 1970; Pipkin and Bremner, 1970; Schwartz, 1971; Chao and Scandalios, 197l; Whitt et al., 1973; Herrera, 1979; Invanenkov, 1980). In adult Xenopus no such repression of isozymes or structural proteins has as yet been found. From two dimensional gel electrophoresis studies De Robertis and Black (1979) concluded that in X. laevis × X. borealis adult hybrids the protein coding genes of both parents are expressed. The same finding has been reported for LDH (Wall and Blackler, 1974; Vonwyl and Fischberg, 1980b). Recently, a study of hemoglobin of interspecies hybrids (Bfirki, in preparation) came to the same conclusion.
A4
A3B
A2B 2
stages
stag~
12 27 29 35/6 40 45 48 50 52' 58 66
12 27, 45
w
Fig. 2. LDH gene activity in embryonic development of the two hybrids X. 1. victorianus 2 x X. borealis d (A) and X. borealis 9 x X.I. victorianus ~ (B).
E. VONWYL
2O
A4
A4
A3B
A3B
A2B2
A2B2 AB3 B4
"O
== O. X
c
=* eel i
t::¢O tD +~. . . . .
O
¢3 ~
J~
stages
® Fig. 3. LDH isozyme patterns of X.I. victorianus, X. borealis and their hybrid combination (X. 1. victorianus ~2 × X. borealis ~) at stage 66 (adult frogs). The two organs liver and kidney have been analyzed.
Acknowledgements--The author wishes to thank Professor Dr M. Fischberg for facilities and Dr E. Biirki for critically reading the manuscript. This study has been supported by the Georges and Antoine Claraz Foundation and the Fonds National Suisse de la Recherche Scientifique.
REFERENCES
Appella E. and Markert C. L. (1961) Dissociation of lactate dehydrogenase into subunits with guanidine hydrochlordie. Biochem. biophys. Res. Commun. 6, 171-176. Brown D. D., Dawid J. B. and Reeder R. H. (1977) Xenopus borealis misidentified as Xenopus muelleri. Devl Biol. 59, 266-267. Castro-Sierra E. and Ohno S. (1968) Allelic inhibition at the autosomally inherited gene locus for liver alcohol dehydrogenase in chicken-qualine hybrids. Bioehem. Genet. 1, 323-335. Chao S. E. and Scandalios J. G. (1971) Alpha-amylase of
Fig. 4. LDH gene activity in embryonic development of X. clivii.
maize: Differential allelic expression at the amyl-I gene locus, and some physicochemical properties of the isozymes. Genetics 69, 47-61. Claycomb W. C. and Villee C. A. (1971) Lactate dehydrogenase isozymes of Xenopus laevis: Factors affecting their appearance during early development. Devl Biol. 24, 413-427. Davis B. J. (1964) Disc electrophoresis. II. Method and application to human serum proteins. Ann. N.Y. Acad. Sci. 121, 40~427. De Robertis E. M. and Black P. (1979) Hybrids of Xenopus laevis and Xenopus borealis expressed proteins from both parents. Devl Biol. 68, 334~339. Dietz A. A. and Lubrano T. (1967) Separation and quantitation of lactic dehydrogenase isoenzymes by disc electrophoresis. Analyt. Biochem. 20, 246-257. Eggstein M. and Kreutz F. H. (1955) Vergleichende Untersuchungen zur quantitativen Eiweissbestimmung im Liquor und eiweissarmen L6sungen, Klin. Wsehr. 33, 879-884.
LDH in developing Xenopus hybrids Faulhaber I. and Lyra L. (1975a) Ver~inderungen der Aktivit~t und des Isoenzymmusters der LDH (Laktatdehydrogenase) w~ihrend der Entwicklung bei Urodelen und Anuren (Triturus alpestris und vulgaris, Ambystoma mexicanum, Xenopus laevis). Wilhelm Roux Arch. 176, 191-205.
Faulhaber I. and Lyra L. (1975b) Aktivit~it und Isoenzyme der Laktatdehydrogenase in Organen von Amphibien (Xenopus laevis, Ambystoma mexicanum, Triturus alpestris und vulgaris) und der Effekt von Gonadotropin- injektionen auf das Enzym im Fettk6rper des miinnlichen Krallenfosches. Hoppe-Seyler's Z. physiol. Chem. 356, 1277-1281. Goldberg E., Cuerrier J. P. and Ward J. C. (1969) Lactate dehydrogenase ontogeny, paternal gene activation, and tetramer assembly in embryos of brook trout, lake trout, and their hybrids. Biochem. Genet. 2, 335-350. Herrera R. J. (1979) Preferential gene expression of an amylase allele in interspecific hybrids of Xiphophorus. Biochem. Genet. 17, 223-227. Hitzeroth H., Klose J., Ohno S. and Wolf U. (1968) Asynchronous activation of parental alleles at the tissuespecific gene loci observed on hybrid trout during early development. Biochem. Genet. 1, 287-300. Ivanenkov V. V. (1980) Differential expression of allelic carboxylesterase-2 genes in oocytes of loach (Misgurnus fossilis) and heterogeneity of loach oocytes and eggs for the expression of allelic carboxylesterase-2 genes. Biochem. Genet. 18, 365-375. Klose J. and Wolf U. (1970) Transitional hemizygosity of the maternally derived allele at the 6PGD locus during early development of the cyprinid fish Rutilus rutilus. Biochem. Genet. 14, 87-92. Klose J., Hitzeroth H., Ritter H., Schmidt E. and Wolf U. (1969) Persistence of maternal isoenzyme patterns of the lactate dehydrogenase and phosphoglucomutase system during early development of hybrid trout. Biochem. Genet. 3, 91-97. Kunz Y. W. (1973) Changes in lactate dehydrogenase
21
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