Different Notch signaling in cells from calcified bicuspid and tricuspid aortic valves.

AIMS: Calcific aortic valve disease is the most common heart valve disease in the Western world. Bicuspid and tricuspid aortic valve calcifications are traditionally considered together although the dynamics of the disease progression is different between the two groups of patients. Notch signaling is critical for bicuspid valve development and NOTCH1 mutations are associated with bicuspid valve and calcification. We hypothesized that Notch-dependent mechanisms of valve mineralization might be different in the two groups. METHODS AND RESULTS: We used aortic valve interstitial cells and valve endothelial cells from patients with calcific aortic stenosis with bicuspid or tricuspid aortic valve. Expression of Notch-related genes in valve interstitial cells by qPCR was different between bicuspid and tricuspid groups. Discriminant analysis of gene expression pattern in the interstitial cells revealed that the cells from calcified bicuspid valves formed a separate group from calcified tricuspid and control cells. Interstitial cells from bicuspid calcified valves demonstrated significantly higher sensitivity to stimuli at early stages of induced proosteogenic differentiation and were significantly more sensitive to the activation of proosteogenic OPN, ALP and POSTIN expression by Notch activation. Notch-activated endothelial-to-mesenchymal transition and the corresponding expression of HEY1 and SLUG were also more prominent in bicuspid valve derived endothelial cells compared to the cells from calcified tricuspid and healthy valves. CONCLUSION: Early signaling events including Notch-dependent mechanisms that are responsible for the initiation of aortic valve calcification are different between the patients with bicuspid and tricuspid aortic valves.

[Autoinflammatory diseases and kidney involvement]. / Autovospalitel'nye zabolevaniia i porazhenie pochek.

Autoinflammatory disease (AID) is a new concept formulated from the results of studying the pathogenesis of familial periodic fevers, a heterogeneous group of genetically determined diseases characterized by causelessly recurrent exacerbations of the inflammatory process due to genetically determined disorders of innate immunity and accompanied by uncontrolled hypersecretion of interleukin-1 (IL-1). These mechanisms were a basic model for understanding a wide range of rheumatologic and other inflammatory diseases of the internal organs. The late diagnosis of AIDs and their ineffective treatment increase the risk for the development and progression of secondary AA amyloidosis. Elaboration of both clinical and effective laboratory criteria for diagnosing autoinflammation is of great importance for determining the tactics of anti-inflammatory therapy and prevention of complications.

[Serum calgranulin C is a highly sensitive autoinflammation activity indicator in patients with familial periodic fevers].

AIM: To determine the possibility of using the serum proinflammatory calcium-binding protein, or calgranulin C (S100A12), to assess activity and therapeutic efficiency in patients with periodic disease (PD) and other familial periodic fevers (FPFs). SUBJECTS AND METHODS: Thirty-five patients with PD and other FPDs, which were verified by molecular genetic study, were examined. In accordance with the disease activity, the patients were divided into 2 groups. The investigators determined the concentration of S100A12 by solid-phase enzyme immunoassay and that of other acute-phase inflammatory markers (erythrocyte sedimentation rate (ERT), neutrophil counts, and fibrinogen and C-reactive protein (CRP) concentrations). RESULTS: The serum concentration of S100A12 in the stage of disease activity was 466.7 (265.22--851.7) ng/ml, which was significantly higher than in remission (244.29 (118.93--409.85) ng/ml (p=0.000002). The highest S100A12 concentrations were noted in the patients with PD; these were 758.95 (434.80--1035.95) ng/ml; the S100A12 level in the majority of PD patients even during remission remained moderately higher. An investigation of the relationship of A100A12 to genetic variants found no differences between the patients homozygous for M694V and those with other genotypes (p=0.37). Estimation of the time course of therapy-induced changes in the serum S100A12 concentration revealed its considerable reduction (р=0.0018). However, normalization of S100A12 levels was not achieved in PD. The remaining increased S100A12 concentration in these patients may be suggestive of the activity of PD despite the absence of its clinical manifestations. S100A12 as a highly sensitive marker allows more exact evaluation of the anti-inflammatory effect of therapy. The S100A12 identification of the subclinical activity of autoinflammatory diseases made all the more important since traditional inflammatory markers, such as ERT, CRP, fibrinogen, and leukocyte counts, are less sensitive for these purposes. In our study, these markers were within the reference range in remission. No differences were found in the S100A12 levels between the groups with and without amyloidosis (p=0.62). CONCLUSION: S100A12 is a highly sensitive marker for the activity of autoinflammatory diseases and the efficiency of their therapy. The serum level of S100A12 in PD may be used to diagnose the subclinical activity of inflammation, which is of importance in monitoring the risk of amyloidosis.

[Description of a case of severe Q fever].

The paper considers a rare clinical case of severe Q fever in a young man with no compromised premorbid background. It describes and analyzes clinical manifestations and laboratory findings with consideration for the current data available in the literature. The issues of the differential diagnosis, laboratory diagnosis, and treatment of Q fever are discussed.

[Nuclear lamins regulate osteogenic differentiation of mesenchymal stem cells].

Nuclear lamins are the major proteins of nuclear envelope and provide the strength of nuclear membrane as well as the interaction of extra-nuclear structures with components of cell nucleus. Recently, it became clear that lamins not only play a structural role in the cell, but could also regulate cell fate, for example lamins could influence cell differentiation via interaction with components of the Notch signaling pathway. Human mutations in LMNA, encoding lamin A/C lead to diseases commonly referred to as laminopathies. Different mutations cause tissue specific phenotypes that affect predominantly a tissue of mesenchymal origin. The nature of this phenomenon, as well as the mechanisms by which lamins regulate cell differentiation remain poorly understood. The aim of this study was to investigate the effect of different mutations of the LMNA on human mesenchymal stem cell (MSC) osteogenic differentiation, and to explore a possible interaction of lamins and Notch signaling pathway. We modified human MSC with mutant LMNA bearing known mutations with tissue specific phenotype associated with different laminopathies. We have shown that mutations associated with different diseases have different effects on the efficiency of MSC osteogenic differentiation and on the expression of specific osteogenic markers SPP1, IBSP and BGLAP. We have also shown that one of the mechanisms involved in the regulation of MSC differentiation may be an interaction of lamins A/C with components of Notch signaling.

[Human babesiasis].

The paper describes a case of imported babesiasis caused by Babesia microti. This is an account of the second case of babesiasis in the Russian-language medical literature. Its clinical picture and laboratory data in the course of the disease are depicted and analyzed. Its clinical differential diagnosis with malaria and an update on the diagnosis and treatment of babesiasis are discussed.

[Muckle-Wells syndrome caused by a new cryopyrin mutation: effective treatment with interleukin-1 antagonist].

A significant progress in the field of molecular-biological investigations resulted in definition of a new group of systemic diseases referred to as autoinflammatory. This group comprises familial periodic fevers: periodic disease (mediterranean fever), Muckle-Wells syndrome, others cryopirinopathy, TRAPS-syndrome. As shown by case reports, Muckle-Wells syndrome is not a rare disease, its sporadic forms are encountered as well as a less severe variant of cryopirinopathy - nonallergic cold urticaria. Awareness of the physicians in respect of this pathology is essential especially because early diagnosis enables control of this disease with use of biological preparations the spectrum of which tends to expansion. Moreover, arrest of inflammation is necessary for prevention of development and progression of such prognostically poor complication as AA-amyloidosis.

[Genetic polymorphism of flax Linum usitatissimum based on use of molecular cytogenetic markers].

Using a set of approaches based on the use of molecular cytogenetic markers (DAPI/C-banding, estimation of the total area of DAPI-positive regions in prophase nuclei, FISH with 26S and 5S rDNA probes) and the microsatellite (SSR-PCR) assay, we studied genomic polymorphism in 15 flax (Linum usitatissimum L.) varieties from different geographic regions belonging to three directions of selection (oil, fiber, and intermediate flaxes) and in the k-37 x Viking hybrid. All individual chromosomes have been identified in the karyotypes of these varieties on the basis of the patterns of differential DAPI/C-banding and the distribution of 26S and 5S rDNA, and idiograms of the chromosomes have been generated. Unlike the oil flax varieties, the chromosomes in the karyotypes of the fiber flax varieties have, as a rule, pericentromeric and telomeric DAPI-positive bands of smaller size, but contain larger intercalary regions. Two chromosomal rearrangements (chromosome 3 inversions) were discovered in the variety Luna and in the k-37 x Viking hybrid. In both these forms, no colocalization of 26S rDNA and 5S rDNA on the satellite chromosome was detected. The SSR assay with the use of 20 polymorphic pairs of primers revealed 22 polymorphic loci. Based on the SSR data, we analyzed genetic similarity of the flax forms studied and constructed a genetic similarity dendrogram. The genotypes studied here form three clusters. The oil varieties comprise an independent cluster. The genetically related fiber flax varieties Vita and Luna, as well as the landrace Lipinska XIII belonging to the intermediate type, proved to be closer to the oil varieties than the remaining fiber flax varieties. The results of the molecular chromosomal analysis in the fiber and oil flaxes confirm their very close genetic similarity. In spite of this, the combined use of the chromosomal and molecular markers has opened up unique possibilities for describing the genotypes of flax varieties and creating their genetic passports.

[Methodological issues of cognitive impairment studies in pediatric multiple sclerosis patients]. / Metodologicheskie problemy issledovaniia kognitivnykh narushenii u detei i podrostkov s rasseiannym sklerozom.

The article provides a review of the characteristics of cognitive impairment in multiple sclerosis (MS) and methods for its assessment in children. The features of the most frequently used neuropsychological batteries, with consideration of specifics of cognitive impairment in MS, and data on assessment of a state of cognitive functions obtained using neuropsychological tests are presented. The authors also discuss the issue of a long-term impact of the disease on a state of cognitive functions. Clinical factors, which can lead to cognitive impairment (type of multiple sclerosis, age at manifestation, number of relapses), are described.

SNF472, a novel anti-crystallization agent, inhibits induced calcification in an in vitro model of human aortic valve calcification.

The purpose of the present study was to investigate whether SNF472, the hexasodium salt of myo-inositol hexaphosphate (IP6 or phytate): 1. Inhibits induced calcification in cultured aortic valve interstitial cells (VIC) as an in vitro model of aortic valve stenosis and 2. Whether inhibition is different in VIC obtained from healthy and calcified aortic valves. VIC from healthy (n = 5) and calcified (n = 7) human aortic valves were seeded in basic growth medium, osteogenic differentiation medium alone, or in osteogenic medium with SNF472 (3, 10, and 30 µM) and cultivated for 3 weeks. Calcification was quantified spectrophotometrically after Alizarin Red staining. In VIC from calcified valves, a complete inhibition of calcification was observed with SNF472 concentrations of 10 and 30 µM (p < .01), significantly stronger than in VIC from healthy valves. When SNF472 was added to VIC after 1 week in osteogenic medium, 30 and 100 µM SNF472 inhibited the progression of ongoing calcification by 81 and 100% (p < .01), respectively. The same concentrations of SNF472 given after 2 weeks reduced calcification by 35 and 40% respectively (not significant). SNF472 inhibited both the formation and the progression of calcification with the strongest effect in VIC from calcified valves.

Investigating patterns and processes of demographic variation: environmental correlates of pre-breeding survival in red-billed choughs Pyrrhocorax pyrrhocorax.

1. Quantifying the pattern of temporal and spatial variation in demography, and identifying the factors that cause this variation, are essential steps towards understanding the structure and dynamics of any population. 2. One critical but understudied demographic rate is pre-breeding survival. We used long-term colour-ringing data to quantify temporal (among-year) and spatial (among-nest site) variation in pre-breeding survival in red-billed choughs (Pyrrhocorax pyrrhocorax) inhabiting Islay, Scotland, and identified environmental correlates of this variation. 3. Random-effects capture-mark-recapture models demonstrated substantial temporal and spatial process variance in first-year survival; survival from fledging to age 1 year varied markedly among choughs fledged in different years and fledged from different nest sites. Spatial variance exceeded temporal variance across choughs fledged from well-studied nest sites. 4. The best-supported models of temporal variation suggested that first-year survival was higher in years following high tipulid larvae abundance and when weather conditions favoured increased invertebrate productivity and/or availability to foraging choughs. These variables explained up to 80% of estimated temporal process variance. 5. The best-supported models of spatial variation suggested that first-year survival was higher in choughs fledged from nest sites that were further from exposed coasts and closer to flocking areas, and surrounded by better habitat and higher chough density. These variables explained up to 40% of estimated spatial process variance. 6. Importantly, spatio-temporal models indicated interactive effects of weather, tipulid abundance, local habitat and local chough density on first-year survival, suggesting that detrimental effects of poor weather and low tipulid abundance may be reduced in choughs fledged from nest sites surrounded by better foraging habitat and lower chough density. 7. These analyses demonstrate substantial temporal and small-scale spatial variation in pre-breeding survival, a key demographic rate, and indicate that this variation may reflect interactive effects of weather, prey abundance, habitat and geography. These patterns illustrate the value of holistic models of demographic variation, and indicate environmental factors that may limit the growth rate of Islay's protected chough population.

[A study of DNA depolyploidization and depolytenization of the heterochromatized gonosomal chromatin bodies in the secondary giant trophoblast cells of the field vole Microtus rossiaemeridionalis using cytophotometry].

A study was made of the distribution of the heterochromatized gonosomal chromatin bodies (GCB) material in the course of nuclear fragmentation of secondary giant trophoblast cells resulting in polykaryocyte formation at the late stage of their differentiation. A simultaneous DNA cytophotometry in GCBs and nuclear fragments showed a progressive GCB DNA content decrease proportional to that of DNA content in nuclear fragments. DNA contents in the nuclear fragments corresponded to 2c, 4c and 8c. In most cases 1-2 GCBs were found in the nuclear fragments of different ploidy levels. Both the total DNA content in GCBs and the DNA content in separate GCBs well correlated with the ploidy levels of fragments. The data obtained demonstrate a regular, whole-genome distribution of chromosomal materials into the nuclear fragments exemplified by sex chromosome distribution in compliance with the ploidy of nuclear fragments. We discuss a possible mechanism of nuclear fragmentation that may ensure substantially a balanced genome of nuclear fragments without leading to mitotic cycle renewal in the giant trophoblast cell population.

[Epidemiology and risk factors of chronic renal diseases: a regional level of the problem].

AIM: Assessment of chronic renal disease (CRD) prevalence and morbidity rate and approaches to early CRD in one of the regions of the RF (Tyva Republic). MATERIAL AND METHODS: A population study in the Tyva Republic performed from 01.07.2003 to 30.06.2004 included patients with glomerular filtration rate (GFR) < 30 ml/min, nephrosclerosis signs at autopsy, terminal GFR < 30 ml/min, on replacement renal therapy (RRT). CRD prevalence and morbidity were estimated (stage IV-V). Examination of 374 Tyva citizens was made for estimation of early CRD and risk factors of developing CRD (the sectional study). The participants of the sectional study were examined clinically and biochemically with measurement of albuminuria, calculation of urine albumin/creatinine (ACR) and study of some molecular-genetic characteristics. RESULTS: Prevalence of CRD stage IV-V in Tyva population was 493 cases per million, prevalence of RRT--126 cases per million. Elevated ACR was found in 4.7% of healthy subjects and 15.9% of hypertensive subjects. Initial lowering of GFR occurred in some healthy subjects and in 1 of 12 hypertensive patients. Significant predictors of albuminuria were serum albumin concentration (p < 0.00001), GFR (p < 0.0002), a male sex (p < 0.004), diabetes mellitus (DM) (p = 0.0057) and left ventricular myocardial mass index (p = 0.0253). GFR depended significantly on age (p < 0.000001), male sex (p < 0.000001), uric acid concentration in the serum (p < 0.000001), presence of DM (p = 0.000019), ACR (p = 0.0059), diastolic pressure (p = 0.0347), triglyceridemia (p = 0.0369). Citizens of Tyva had more frequently than citizens of other regions of Russia IlI-genotype of angiotensin 1-converting enzyme (ACE) (p < 0.0001), T-allele of methylentetrahydrofolatereductase (p < 0.0001), E3-allele of gene of apoprotein E (p < 0.0001). Prevalence of aa, ab, bb genotypes of eNO-synthetase was 82.3%, 15% and 2.7% in the group of Tyva examinees vs 62, 31 and 7% in European Russians (p < 0.01). CONCLUSION: Prevalence of both early and advanced stages of CRD among population of Tyva Republic is rather high. CRD morbidity may depend, besides conventional risk factors, some genetic specific features. Screening studies require continuation for early detection of CRD and timely planning of therapeutic and preventive measures.

[Assessment of the intensity of lymphocyte blast transformation in the crypts of the palatal tonsils by using DNA cytophotometry]. / Otsenka intensivnosti blastnoi transformatsii limfotsitov v kriptakh nebnykh mindalin s pomoshch'iu tsitofotometrii DNK.

Cell fractions isolated from lacunae of palatine tonsils with different functional activities were taken from 40 children 6-15 years of age. The cell fractions were examined using vital phase-contrast microscopy, light microscopy of Pappenheim-stained smears and the Feulgen cytophotometry. Lymphocytes with signs of immunological involvement were shown to constitute 95 per cent of the whole cell lacunar population of the active functional tonsils. 35 per cent of lymphocytes, being in different stages of blast transformation, were found. The most intense blast transformation was revealed in patients with tonsil inflammation. 5-13 per cent of lacunar nuclei with DNA content above the diploid level were found in these patients. Some multicellular islets accumulating small lymphocytes, lymphocytes at different stages of blast transformation, and macrophages were revealed to imitate the cooperation of immunocompetent cells. The data obtained can be helpful in the practical surgery of palatine tonsils.

[Cytophotometric analysis of the protein and nucleic acid content of the nucleus and cytoplasm of resting and proliferation-activated hepatocytes in the mouse]. / Tsitofotometricheskii analiz soderzhaniia belkov i nukleinovykh kislot v iadre i tsitoplazme pokoiashchikhsia i aktivirovannykh k proliferatsii gepatotsitov myshi.

Mouse hepatocytes, quiescent and activated to proliferation after hepatectomy, were investigated using cytophotometry in the ultraviolet region of selective absorbtion of nucleic acids, and then were examined in the visible region of spectrum after cytochemical reaction for total protein. Some features of RNA and protein accumulation were revealed in the nucleus and cytoplasm of activated cells of different ploidy. The activation resulted in the reduction of histone content and in the increase in the nucleus: cytoplasm ratio in cells of all the ploidy classes.

[Cytophotometric study of the DNA in the lymphocytes from human lymph nodes in culture]. / Tsitofotometricheskoe issledovanie DNK v limfotsitakh iz limfaticheskikh uzlov cheloveka v kul'ture.

In the suspension culture of lymph node cells taken from patients with exzemic erythroderma, an active blast-transformation of lymphocytes starts in 24 hours, whereas in patients with mycosis fungoides this begins only in 48 hours. In lymphocytes taken from patients with mycosis fungoides, a tendency to a slower increase in DNA quantity was noticed compared to that in patients with exzemic erythrodermy. The differences observed may be used for diagnostic purposes.

[Cytophotometric and electron microscopic studies of chronic human skin lymphomas. II. Research on lymph node involvement]. / Tsitofotometricheskoe i élektronno-mikroskopicheskoe issledovaniia khronicheski protekaiushchikh limfom kozhi cheloveka. II. Issledovanie porazheniia limfaticheskikh uzlov.

Results of electron microscopic and cytophotometric studies of biopsy material from lymph nodes of patients with cutaneous lymphomas with low degree of malignancy are discussed, with special reference to early diagnostic criteria of the disease. Specific characteristics of tumor tissue involve the presence of atypical lymphocytes with marginal condensed chromatin extrusions of nuclear material, deep invaginations of the nuclear membrane, nuclear pockets, excess of the mean DNA content per nucleus above the diploid standard level, more than 5% of nuclei being in the hyperdiploid area. Electron microscopic and cytophotometric methods allowed to diagnose the tumor injury of lymph nodes, when the traditional histological techniques revealed no signs of malignancy.

[Nature of the orientation of the tryptophan residues in the myosin and actin from striated muscle fiber]. / O kharaktere orientatsii triptofanovykh ostatkov v miozine i aktine poperechnopolosatogo myshechnogo volokna.

The mode of tryptophan residue orientation in myosin and action myofilaments of the muscle fiber was studied using polarized ultraviolet (UV) fluorescent microscopy of the muscle fiber was studied using polarized ultraviolet (UV) fluorescent microscopy technique. During an elective extraction of proteine from thick and thin myofillaments changes in UV fluorescence anisotropy of muscle fibers were detected, thus suggesting that tryptophanil residues in myosin may be oriented by their own short axes mostly parallel, but in actin--perpendicular to the muscle fiber axis. The use of acrylamide, an UV fluorescence quencher, is proposed for the control of extraction electivity of proteins from muscle fibers.

[Study of structural changes of contractile muscle proteins with the aid of polarization ultraviolet fluorescence microscopy. 1. Conformational changes of F-actin in the muscle fiber caused by ATP and its analogs]. / Izuchenie strukturnykh izmenenii sokratitel'nykh belkov myshechnogo volvokna s pomoshch'iu poliarizatsionnoi ul'trafioletovoi fluorestsentn*56i mikroskopii. 1. Konformatsionnye izmeneniia F-aktina v myshechnom volokne, vyzvannye ATF i ego analogami.

Increase of anisotropy of F-actin fluorescence of balanus and rabbit muscle fibers under the influence of ATP, AMP and pyrophosphate in EGTA presence was detected by means of the polarized ultraviolet (UV) fluorescent microscopy methods. The fluorescence anisotropy changes are assumed to be associated with the conformational changes in the actin. ATP cause more noticeable changes of actin structure, than pyrophosphate and AMP. The conformational changes in the actin of balanus and rabbit muscle fibres were similar. ATP and its analogs induced also decrease of UV fluorescence anisotropy of A-band which appears to be associated with conformational changes in myosin. It was siggested that the changes in fluorescence of anisotropy of A-bands are due to structural changes in both HMM and LMM parts of myosin molecule.

[Quantitative investigation of reproduction of condensed chromatin of sex chromosomes during trophoblast cell polyploidization and endoreduplication in the East European field vole Microtus rossiaemeridionalis]. / Kolichestvennoe issledovanie reproduktsii kondensirovannogo khromatina polovykh khromosom pri poliploidizatsii i éndoreduplikatsii kletok trofoblasta vostochonoevropeiskoi polevki Microtus rossiaemeridionalis.

Simultaneous measurement of DNA content in cell nuclei and condensed chromatin bodies formed by heterochromatized regions of sex chromosomes (gonosomal chromatin bodies, GCB) has been performed in two trophoblast cell populations of the East-european field vole Microtus rossiaemeridionalis, namely in the proliferative population of trophoblast cells of the junctional zone of placenta and in the secondary giant trophoblast cells. One or two gonosomal chromatin bodies have been observed in trophoblast cell nuclei of all embryos studied (perhaps both male and female), In the proliferative trophoblast cell population, characterized by low ploidy levels (2c-16c), and in the highly polyploid population of secondary giant trophoblast cells (16c-256c), the total DNA content in GCB increased proportionally to the ploidy level. In separate bodies, the DNA content rose also in direct proportion with the ploidy level seen in the nuclei with both one and two GCBs in the two trophoblast cell populations. A certain increase in percentage of the nuclei with 2-3 GCBs was shown in the nuclei of the junctional zone of placenta; this may be accounted for by genome multiplication via uncompleted mitoses. In the secondary giant trophoblast cell nuclei (16c-256c), the number of GCBs did not exceed 2, and the share of nuclei with two GCBs did not increase, thus suggesting the polytene nature of sex chromosome in these cells. At different poloidy levels, the ratio of DNA content in the nucleus to the total DNA content in GCB did not change significantly giving evidence of a regular replication of sex chromosomes in each cycle of genome reproduction. In all classes of ploidy, the mean total DNA content in trophoblast cell nuclei with single heterochromatic body was less than in the nuclei with two and more GCBs. This may indicate that a single GCB in many cases does not derive from the fusion of two GCBs. To put it another way, in the nuclei with one GCB and in those with two or more GCBs, different chromosome regions may undergo heterochromatization. The regularities observed here are, most probably, associated with the peculiarities in the structure of X- and Y-chromosomes in a range of species of Microtus (M. agrestis, M. rossiaemeridionalis, M. transcaspicus). As a result, gonosomal chromatin bodies may include large blocks of both constitutive heterochromatin of X- and Y-chromosomes (in male and female embryos) and inactivated euchromatin of "lyonized" X-chromosome in female embryos. Therefore the presence of two or more GCBs in trophoblast cells of M. rossiaemeridionalis may be accounted for by both polyploidy and functional state of the nucleus, in which gonosomal constitutive heterochromatin and inactivated euchromatin form two large chromocenters rather than one. The differences in DNA content in GCBs in the nuclei with one and two GCBs seem to be an indirect indication that the two chromocenters may be formed by two different gonosomes, with the extent of their heterochromatization being higher than that in the nuclei with one GCB. GCBs in the trophoblast cells of M. rossiaemeridionalis are observed not only at the early developmental stages, as it was observed in rat at the first half of pregnancy (Zybina and Mosjan, 1967), but also at the later stages, up to the 17th day of gestation. At these stages, the nuclei with non-classical polytene chromosomes rearrange to those with a great number of endochromosomes, probably because of disintegration of chromosomes into oligotene fibrils. However, it does not seem unlikely that this process may involve heterochromatized gonosomal bodies, since only one or two large GCBs can be seen in the nuclei as before. The presence of prominent blocks of constitutive heterochromatin seems to favor a closer association of sister chromatids in polytene chromosomes, which prevents their dissociation into endochromosomes with the result that polyteny of sex chromosomes in the field vole trophoblast is probably retained during a longer period of embryonic development.