The effects of temperature and chorionic gonadotropin on the functional properties of lactate dehydrogenase from oocytes of loach Misgurnus fossilis

Acclimation of loach to relatively low and high temperatures gives rise to changes in the properties of LDH from oocytes. The minimum of apparent K_m values for pyruvate of LDH from immature oocytes of fish acclimated to low temperature was registered at low assay temperatures, whereas adaptation to high temperatures leads to the enzyme showing a minimum at high temperatures. In thermal acclimation of fish the K_m minimum value drifts during 15 days. During oocyte maturation, the K_m minimum drifts during 40 hr. The differences in the kinetic features of LDH from oocytes both at thermal acclimation and during oocyte maturation are not associated with the appearance of new isozymes.     

Evidence for evolutionary changes in ontogeny: Paleontological, comparative-morphological, and molecular aspects

It has been noted that the integration of modern data of paleontology, comparative morphology, developmental biology, and molecular genetics forms the basis for understanding the mechanisms of evolutionary transformations of ontogeny. Paleontological and morphological evidence of the evolutionary changes in ontogeny are considered based on the data of cell and molecular biology and developmental genetics. It is shown that reorganizations of gene regulatory cascades (mainly Hox genes) play a key role in the evolution of the axial organization of animals and modifications of the limb structure of metazoans, whereas the formation of new types of structures was apparently determined by the emergence of new populations of stem cells in embryogenesis (for example, neural crest cells in the evolution of vertebrates).     

Differential expression of duplicated LDH-A genes during temperature acclimation of weatherfish Misgurnus fossilis. Functional consequences for the enzyme

Temperature acclimation in poikilotherms entails metabolic rearrangements provided by variations in enzyme properties. However, in most cases the underlying molecular mechanisms that result in structural changes in the enzymes are obscure. This study reports that acclimation to low (5 degrees C) and high (18 degrees C) temperatures leads to differential expression of alternative forms of the LDH-A gene in white skeletal muscle of weatherfish, Misgurnus fossilis. Two isoforms of LDH-A mRNA were isolated and characterized: a short isoform (= 1332 bp) and a long isoform ( = 1550 bp), which both have 5'-UTRs and ORFs of the same length (333 amino acid residues), but differ in the length of the 3'-UTR. In addition, these two mRNAs have 44 nucleotide point mismatches of an irregular pattern along the complete sequence, resulting in three amino acid mismatches (Gly214Val; Val304Ile and Asp312Glu) between protein products from the short and long mRNA forms, correspondingly LDH-A(alpha) and LDH-A(beta) subunits. It is expected that the beta-subunit is more aliphatic due to the properties of the mismatched amino acids and therefore sterically more restricted. According to molecular modelling of M. fossilis LDH-A, the Val304Ile mismatch is located in the subunit contact area of the tetramer, whereas the remaining two mismatches surround the contact area; this is expected to manifest in the kinetic and thermodynamic properties of the assembled tetramer. In warm-acclimated fish the relative expression between alpha and beta isoforms of the LDH-A mRNA is around 5 : 1, whereas in cold-acclimated fish expression of is reduced almost to zero. This indicates that at low temperature the pool of total tetrameric LDH-A is more homogeneous in terms of alpha/beta-subunit composition. The temperature acclimation pattern of proportional pooling of subunits with different kinetic and thermodynamic properties of the tetrameric enzyme may result in fine-tuning of the properties of skeletal LDH-A, which is in line with previously observed kinetic and thermodynamic differences between 'cold' and 'warm' LDH-A purified from weatherfish. Also, an irregular pattern of nucleotide mismatches indicates that these mRNAs are the products of two independently evolving genes, i.e. paralogues. Karyotype analysis has confirmed that the experimental population of M. fossilis is tetraploid (2n = 100), therefore gene duplication, possibly through tetraploidy, may contribute to the adaptability towards temperature variation.     

Correlation of ontogenetic and evolutionary processes in view of achievements of modern genetics: Role of gene duplication

I.I. Schmalhausen’s concept about the interrelation of individual and historical development is analyzed from the positions of modern developmental biology and molecular genetics. The role of gene duplication in evolutionary, ontogenetic, and adaptable processes is discussed. The data on mechanisms of functional diversification of duplicated genes (exon-intron structural changes and point mutations) in these processes are submitted. The modern synthesis outlook in developmental biology is regarded.     

Evolutionary mechanisms: Modularity,morphogenetic fields of gene expression,genetic regulation

Modern concepts heterochrony mechanisms, taking into account the data on modularity of ontogenetic and evolutionary processes, morphogenetic fields of gene expression are considered. In the context of evolutionary changes, features of genetic regulation of heterochronies, and also suppression of gene activity by epigenetic regulation are analyzed. Features of the origin of evolutionary novelties due to heterochronies, macromutations, and divergence of duplicated genes, which result in the formation of new genes and gene families, are discussed.     

Features of Ca<Superscript>2+</Superscript> signaling in proliferating and in differentiating murine myoblasts

The state of the Ca²⁺ signaling system has been assessed in proliferating and in differentiating C2C12 myoblasts. Proliferating myoblasts exhibit no features of a functional system: the intracellular ATP-controlled Ca²⁺ store is low (perhaps only mitochondrial) and no Ca²⁺ entry from the medium is registered upon its exhaustion, there is no cytosolic response to KCl-induced depolarization. The Ca²⁺ signaling system starts to form at the early stages of differentiation (within 10 h after transfer of cells to the differentiation medium). This is seen as appearance of capacitive and voltage-dependent Ca²⁺ entry and its accumulation in the endoplasmic reticulum. A small contribution to the ATP-evoked rise in cytosolic Ca²⁺ is also made by mitochondria.     

Regulation of Ca<Superscript>2+</Superscript> influx in proliferating and differentiating murine myoblasts with participation of L-type Ca<Superscript>2+</Superscript> channels

The basic mechanisms of regulation of Ca²⁺ influx have been studied in murine myoblasts proliferating and differentiating in culture. The presence of L-type Ca²⁺ channels in proliferating myoblasts is shown for the first time. It is also shown that the influx of Ca²⁺ through these channels is regulated by the adrenergic system. The influx of Ca²⁺ after activation of the adrenergic system by addition of adrenaline has been estimated in comparison with the contribution of reticular stocks exhausted by ATP in calcium-free medium. The Ca²⁺ influx in proliferating myoblasts is regulated by β-2 adrenergic receptors whose action is mediated by adenylate cyclase through L-type calcium channels. In differentiating myoblasts, the adrenaline-induced Ca²⁺ influx is substantially lower than in proliferating cells, and maximal influx of Ca²⁺ may be reached only upon exhaustion of reticular stocks.