Extensive heterozygosity at three enzyme loci in hybrid sunfish populations

A natural hybrid of Leuciscus cephalus and Alburnus alburnus (Pisces, Cyprinidae) from the Ibar River, Western Serbia

The hybrid Leuciscus cephalus ? Alburnus alburnus was recognized in studying structure of the ichthyofauna of the middle course of the Ibar River, a right-hand tributary of the Western Morava (system of the Danube on the territory of Serbia). It is a hybrid reciprocal to the natural hybrid Alburnus alburnus ? Leuciscus cephalus from the same river system (the Gruza River, a left-hand tributary of the Western Morava), which was described previously by the present author. The hybrid was identified on the basis of its intermediate characteristics and characteristics of the parent species such as pharyngeal bones and teeth; shape of the scales; number, form, and structure of radial canals of the scales; morphology of branchiospinae on the first gill arch; and a complex of meristic and morphometric characters. With respect to its characteristics, this hybrid, like the hybrid Alburnus alburnus ? Leuciscus cephalus, is closer to L. cephalus. However, in general appearance the hybrid more closely resembles the presumed maternal species. The phenomenon of reciprocal hybridization is discussed at some length.

Thermal stability of soluble malate dehydrogenase isozymes of subtropical fish belonging to the orders Characiformes, Siluriformes and Perciformes

Electrophoretic thermostability tests of soluble malate dehydrogenases (sMDH) isozymes in tissue extracts of 21 subtropical fish belonging to the orders Characiformes, Siluriformes and Perciformes showed three distinct results. The first, characterized by thermal stability of the slowest-migrating band or A-isoform, was detected in 52% of all species. The second, exhibited in 29% of the species analyzed, had a bidirectionally divergent pattern of their sMDH locus expression, and was characterized by a nondivergent thermostability pattern of both sMDH-A* and B*. In the third category, obtained in 19% of the species studied (the four Siluriformes species), thermostability of the fastest-migrating bands, or B-isoforms, was observed. Comparison of the effects of habitat temperature on the activity of paralogous and orthologous isoforms in tissue extracts of two of these species with different thermostability properties (Leporinus friderici - thermostable sMDH-A*, and Pimelodus maculatus - reverse thermostability properties or reverse electrophoretic pattern), collected during winter and summer months, showed that A and B subunits were present at different quantitative levels and their activities were nearly season independent. Differences in susceptibility to temperature (50°C) of both sMDH loci from tissue extracts of these species were found. In P. maculatus, these susceptibilities helped strengthen one of the hypotheses: the reverse thermostability pattern, where the fastest-migrating band or the B-isoform was the thermostable sMDH. Thus, temperature differences among orthologous homologues of sMDH seem to have occurred in these acclimatized species, where the fastest-migrating band, usually muscle specific and thermolabile in most teleosts, appeared in P. maculatus as the thermostable isoform.

Lactate dehydrogenase in teleosts. The role of LDH-C4 isozyme

1. Lactate dehydrogenase (LDH) occupies an important position in cell metabolism. 2. Teleosts possess at least three genetic loci coding for lactate dehydrogenase subunits, Ldh-A, Ldh-B and Ldh-c. LDH exists in most tissues in several isozymic forms. 3. The isozyme LDH-C4 is synthesized predominantly in regions of the nervous system concerned with the eye.

Adaptative features of enzymes from family Sciaenidae--III. Studies on lactate dehydrogenase (LDH) of fishes from the south coast of Uruguay

1. Electrophoretic analyses of lactate dehydrogenase isozyme patterns of three species of temperate fish belonging to family Sciaenidae (order Perciformes) indicates that at least three LDH loci--Ldh-A, Ldh-B and Ldh-C are active. 2. The subunits encoded by these loci occurred at different levels in the different tissues and organs analyzed. 3. The products of these loci show different response to changes in temperature. The results were obtained by electrophoretic analyses. 4. Thermostability of skeletal muscle, heart and eye lactate dehydrogenase incubated at 60 degrees C for different periods of time were examined. 5. Relative activities of LDH isozymes were compared by Klebe's method to determine pattern of divergence of duplicated gene expression in the three species studied.

Adaptative features of enzymes from family sciaenidae (Perciformes)--I. Studies on soluble malate dehydrogenase (s-MDH) and creatinine kinase (CK) of fishes from the south coast of Uruguay

1. Electrophoretic analysis of the soluble malate dehydrogenase (s-MDH) and creatine kinase (CK) isozyme patterns of three species of temperate fishes (Scianidae, Perciformes) indicates at least two loci for s-MDH, Mdh-A and Mdh-B, and four CK, Ck-A, Ck-B, Ck-C and Ck-D. 2. The subunits encoded by these loci occurred at different levels in different tissues and organs analyzed. 3. Through electrophoretic analysis the products of these loci showed different behaviour to changes in temperature. 4. Relative activities of s-MDH and CK isozymes were compared by Klebe's (1975) method to determine pattern of divergence of duplicated gene expression in the three studied species.

Adaptative features of ectothermic enzymes--I. Temperature effects on the malate dehydrogenase from a temperate fish Leiostomus xanthurus

1. Following electrophoresis the s-MDH activity of Leiostomus xanthurus and many other species of fish and amphibian appears in three sharp, equally-spaced, anodal bands. Each band is a dimer (AA, AB and BB) and two loci are active. 2. In Leiostomus tissue extracts A and B subunits are present are differing quantitative levels and their activities can be modified by changes in environment temperature. 3. Thermostability and thermal dependency tests show that, similar to what occurs during acclimatization, the AA isozyme is more stable to heat than is the BB isozyme. The BB isozyme is activated by low temperatures and is rapidly inactivated by high temperatures. 4. Extracts from a variety of fishes, amphibians, reptiles and birds suggest that when only one or two s-MDH bands are present, they behave as dose the AA homodimer in Leiostomus Xanthurus, i.e., are stable at elevated temperatures.

Synchronous allelic expression at the glucosephosphate isomerase A and B loci in interspecific sunfish hybrids

Allelic isozymes of glucosephosphate isomerase at the Gpi-A and -B loci were separated by starch gel electrophoresis in the warmouth (Lepomis gulosus) and green sunfish (L. cyanellus). The specific tissue distributions and developmental expressions of the GPI-A2, -AB, and -B2 isozymes were not different between these two species. The synchrony of allelic expression in normal intraspecific sunfish crosses was demonstrated by means of an electrophoretic variant at the Gpi-B locus. In embryos formed from warmouth x green sunfish hybrid crosses, the paternal GPI-A2 isozymes were first expressed at the same time in both reciprocal hybrids, at 21-25 hr after fertilization. The maternal and paternal GPI-B subunits were synchronously expressed in reciprocal hybrids just for prior to hatching. The parental allelic isozymes at both loci shoed codominant expression in all tissues of the mature F1 hybrids. These results are consistent with the absence of allelic asynchrony and inhibition in interspecific hybrids formed from more evolutionarily related species.

Differential gene expression in multilocus isozyme systmes of the developing green sunfish

The patterns of expression of eight multilocous isozyme systems were investigated in the differentiated adult tissues and the early embryonic stages (0-210 hours after fertilization) of the green sunfish, Lepomis cyanellus. Enzymes encoded by approximately 23 gene loci were resolved by starch-gel electrophoresis and detected by specific histochemical staining. The developmental patterns of these isozyme systems appear to be the result of the diffential expression of the multiple gene loci. Isozymic forms of glucoseophosphate isomerase (GPI-A2), malate dehydrogenase (MDH-A2), and creatine kinase (CK-C2) were present in most differentiated tissues, in the unfertilized eggs, and in all stages of embryonic development. Closely homologous forms of these isozymes (GPI-B2, MDH-B2, and CK-A2) were expressed predominantly in skeletal muscle and were first detected at around the time of hatching (38-42 hours). The similar temporal and spatial patterns of gene expressions for the GPI, LDH, MDH, and CK loci suggest that the duplicates loci encoding enzymes, diverged in their regulation to patterns of differential gene expression which are similar for each enzyme system.