D. A. Nikishin

Expression of serotonergic system components during early Xenopus embryogenesis

Despite abundant research studies on the physiological and biochemical nature of embryonic neurotransmitter function, little is known about the molecular genetic mechanisms involved. The expression of the main components of the serotonergic system during early Xenopus embryogenesis was investigated using RT-PCR, real time PCR and in situ hybridization. Transcripts encoding the serotonin receptors HTR2C and HTR7, as well as the vesicular monoamine transporter VMAT2, the serotonin transporter (SERT) and the serotonin synthesis enzymes tryptophan hydroxylase (TPH2) and aromatic amino acid decarboxylase (AAAD) were found to be expressed during the cleavage division stages, whereas the degradation enzyme monoamine oxidase A (MAOA) was absent. The main components of the serotonergic system were found to be expressed during the earliest stages of embryonic development. The embryonic transmitter mechanism, its complexity, and its variability among various species are discussed.

Ladder-shaped ion channel ligands: Current state of knowledge

Ciguatoxins (CTX) and brevetoxins (BTX) are polycyclic ethereal compounds biosynthesized by the worldwide distributed planktonic and epibenthic dinoflagellates of Gambierdiscus and Karenia genera, correspondingly. Ciguatera, evoked by CTXs, is a type of ichthyosarcotoxism, which involves a variety of gastrointestinal and neurological symptoms, while BTXs cause so-called neurotoxic shellfish poisoning. Both types of toxins are reviewed together because of similar mechanisms of their action. These are the only molecules known to activate voltage-sensitive Na+-channels in mammals through a specific interaction with site 5 of its α-subunit and may compete for it, which results in an increase in neuronal excitability, neurotransmitter release and impairment of synaptic vesicle recycling. Most marine ciguatoxins potentiate Nav channels, but a considerable number of them, such as gambierol and maitotoxin, have been shown to affect another ion channel. Although the extrinsic function of these toxins is probably associated with the function of a feeding deterrent, it was suggested that their intrinsic function is coupled with the regulation of photosynthesis via light-harvesting complex II and thioredoxin. Antagonistic effects of BTXs and brevenal may provide evidence of their participation as positive and negative regulators of this mechanism.

Transmitters in Blastomere Interactions

Normal multicellular organism develops from fertilized egg cell, although the latter may give birth for twins too. Mechanisms that lead to the realization of these variants of the development may differ greatly, however, it naturally suggests itself that such deviation as twin formation is conditioned by this or that disturbance of cellular interactions. But the very fact of the existence of such interactions after classic experiments remained disputable until now. Naturally, far less is known on the suggested mechanisms of such interactions that provide the formation of integral organism or, correspondingly, their distortion that lead to the twins formation.

Expression and functional activity of neurotransmitter system components in sea urchins’ early development

Reverse-transcription polymerase chain reaction (RT-PCR) investigation of the expression of the components supposedly taking part in serotonin regulation of the early development of Paracentrotus lividus has shown the presence of transcripts of five receptors, one of which has conservative amino acid residues characteristic of monoaminergic receptors. At the early stages of embryogenesis the expressions of serotonin transporter (SERT) and noradrenaline transporter (NET) were also recognized. The activities of the enzymes of serotonin synthesis and serotonin transporter were shown using immunohistochemistry and incubation with para-chlorophenylalanine (PСРА) and 5-hydroxytryptophan (HTP). Pharmacological experiments have shown a preferential cytostatic activity of ligands characterized as mammalian 5-hydroxytryptamine (5-HT)1-antagonists. On the basis of the sum of the data from molecular biology and embryo physiological experiments, it is suggested that metabotropic serotonin receptors and membrane transporters take part in the regulatory processes of early sea urchin embryogenesis.

Expression of transmitter receptor genes in early development of sea urchin Paracentrotus lividus

Neurotransmitters (including serotonin and acetylcholine) perform a number of prenervous functions in early sea urchin development. To detect the particular receptor components involved in these processes, we carried out a database search and nucleotide sequences homologous to serotonin receptor type 4, and the α6- and α10-subunits of nicotinic acetylcholine receptor were found among EST-clones from early Paracentrotus lividus embryos. Expression of these transcripts during early development was demonstrated using RT-PCR. These results are the first molecular biology evidence of serotonin and acetylcholine receptor expression in sea urchin early embryogenesis.

Expression of Components of the Serotonergic System in Folliculogenesis and Preimplantation Development in Mice

The functions of serotonin include the growth and development regulation of female germ cells as well as early embryo development. RT-PCR analysis of mRNA expression of the genes of the enzymes for synthesis and degradation and transporters and receptors of serotonin during folliculogenesis and preimplantation development of mice was performed to discover the particular mechanisms of these functions. The mRNA of tryptophan hydroxylase tph1 and monoaminoxidase maoa; membrane transporter sert and vesicular transporter vmat2; and serotonin receptors htr1b, htr1d, htr2a, htr5b, and htr7 were revealed in granulosa cells. The expression of mRNA of the aromatic amino acid decarboxylase ddc and the htr2b receptor additionally appears in the yellow body. The expression of mRNA of the genes of the tph2, ddc, and maoa enzymes; the sert, vmat1, and vmat2 transporters; and quite a number of receptors is observed during the preimplantation development, and it is transitory in most of them. The expression of all components and its dynamics suggest that the serotonergic signaling system is functionally active in mouse folliculogenesis and preimplantation development.

Effects of mechanical stretching of embryonic tissues on axial structure formation in Xenopus laevis

Effect of mechanical stretch on the differentiation of axial anlages and Chordin gene expression was studied in sandwich explants prepared from embryonic tissues of Xenopus laevis at the early gastrula stage in two variants: with dissected or intact dorso-medial region. In the first case, convergent cell movements were suppressed and properly organized axial organs (notochord and somites) were almost completely absent. However, they developed if the explants of such type were artificially stretched in the ventro-dorsal direction. In this case, axial organs elongated in the line of stretching, that is in the direction vertical to their normal orientation. Segmented mesoderm was always in contact with the chord anlage. In situ hybridization revealed that the area of Chordin gene expression was also extended in the direction of stretching. PCR showed that Chordin gene expression in stretched explants with disrupted dorso-medial region was statistically at the same level as in the explants with intact dorso-medial region. At the same time, the corresponding gene expression in unstretched explants with disrupted dorso-medial region was statistically higher. The obtained data indicate that mechanical stretch and associated cell movements are a necessary and sufficient condition for the formation of proper histological structure of axial organs and regulation of Chordin gene expression.

Role of gap junctions and mechanosensitive ion channels in the mechanisms of growth pulsations of Gonothyraea loveni

64 Growth and morphogenesis of all rudiments of colonial hydroid polyps occurs due to pulsation of a specialized apical portion of the colony body, the growing tips. Growth pulsation is a result of recurrent proximal–distal waves of contractions and relaxations of epi and gastrodermal cells. There is no prolifera tion within the growing tips and growth is exclusively due to cell movements [1]. The shape of a developing rudiment is directly dependent on the growth pulsa tion parameters in the course of natural or experimen tal apical growth [2]. The mechanisms underlying growth pulsation of hydroid polyps are of interest because hydroid polyps represent a simple and con trollable model of the epithelial morphogenesis, which is widely involved in organogenesis of many animals, including mammals.