Polytene chromosomes in mammalian cells.

This article deals with the structural and functional organization of polytene chromosomes in mammals. Based on cytophotometric, autoradiographic, and electron microscopic data, the authors put forward a concept of nonclassic polytene chromosomes, with special reference to polytene chromosomes in the mammalian placenta. In cells with nonclassic polytene chromosomes, two phases of the polytene nucleus cycle are described, such as the endointerphase (S phase) and endoprophase (G phase). The authors generalize that the main feature of nonclassic polytene chromosomes is that forces binding the sister chromatids are much weaker than in the Diptera classic polytene chromosomes. This concept is confirmed by comparative studies of human, mink, and fox polytene chromosomes. The final step of the trophoblast giant cell differentiation is characterized by a transition from polyteny to polyploidy, with subsequent fragmentation of the highly polyploid nucleus into fragments of low ploidy. Similarities and dissimilarities of pathways of formation and rearrangement of nonclassic polytene chromosomes in mammals, insects, plants, and protozoans are compared. The authors discuss the significance of polyteny as one of the intrinsic conditions for performance of the fixed genetic program of trophoblast giant cell development, a program that provides for the possibility of a long coexistence between maternal and fetal allogenic organisms during pregnancy.

[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.

Polyploidization in the trophoblast and uterine glandular epithelium of the endotheliochorial placenta of silver fox (Vulpes fulvus Desm.), as revealed by the DNA content.

Dynamics of genome multiplication during establishment of interrelations between trophoblast and glandular epithelium of the endometrium has been studied in the course of formation of placenta in the silver fox. During formation of the placenta, penetration of the trophoblast into the zone of the endometrial glandular epithelium and of endometrial blood vessels into the zone of expanding trophoblast occurs. The trophoblast, which gradually replaces epithelium and a part of the stroma of the endometrium, closely adjoins endometrial vessels but does not disrupt them, thereby the endotheliochorial placenta is formed. Cytophotometric measurements of the DNA content in trophoblast nuclei have shown that most of them are polyploid: predominantly 4-64c, occasionally 128c and 256c. Polyploidy of the trophoblast may be a consequence of various types of polyploidizing mitoses. Cytophotometric measurements of the DNA content in mitotic figures have revealed the presence of mitoses of diploid cells, i.e. with the DNA amount of 4c (2n), and polyploid cells, i.e. 8c (4n), and 16c (8n), therefore trophoblast cells in the silver fox placenta are able to enter mitosis up to the octaploid level. Higher degrees of polyploidy in the trophoblast cells seem to be achieved by endoreduplication. Polyploidization of the uterine glandular epithelial cells during placentation in the silver fox occurs until the level of 8c. Thus, the tissue-specific response of the uterus to the implanting embryo consists of active proliferation and polyploidization of the glandular epithelium, which may compensate formation of prominent population of decidual cells (i.e., connective tissue cells). In the endotheliochorial placenta of the silver fox the regularity is confirmed that cells of both maternal and fetal origin are, as a rule, polyploid in sites of their contact in placenta, which may be of protective significance in the contact of allogenic organisms.

[Phagocytosis during mitotic and endomitotic chromosome replication in the trophoblast of the grey vole]. / Osobennosti fagotsitoza pri mitoticheskoi i éndomitoticheskoi replikatsii khromosom v trofoblaste seroi polevki

Phagocytosis was studied in three populations of trophoblast cells of the grey vole: primary and secondary giant cells, and spongiotrophoblast. In the two former, the cell growth is accomplished by endomitotic polyploidization only, whereas the spongiotrophoblast cells divide mitotically for a long time. The phagocytosis of these differs from that in giant cells. No more than 1--2 erythrocytes were phagocyted by the spongioblast diploid cells, while giant cells were able to phagocyte over several dozens of erythrocytes. The spongioblast cells are haemophagous and phagocyte only anucleate blood cells -- erythrocytes; unlike, giant cells, when ingrowing within the uterus mucose, are capable of taking up and digesting, in addition to erythrocytes, leukocytes, decidual and endothelial cells.

[Phagocytic activity and reproduction of the trophoblast cells in the embryo of albino rat]. / Fagotsitarnaia aktivnost' i reproduktsiia kletok trofoblasta u zarodyshei beloi krysy

The phagocytic activity of primary and secondary giant cells of the white rat's trophoblast was studied in the course of differentiation. The highest activity occurs in the initial period of the foetus implantation to last within a limited time for 5--6 days. Both quantitative and qualitative differences were detected in phagocytic activities of the trophoblast cells during their growth. A question is discussed of the time synchronism between the phagocytic activity and the trophoblast cells polyploidization.

[An electron microscopic study of lamp-brush chromosomes and the products of their activity during rabbit oogenesis]. / Elektronnomikroskopicheskoe issledovanie khromosom tipa lampovykh shchetok i produktov ikh aktivnosti v oogeneze krolika

An ultrastructural study of the rabbit oocyte nucleus was started from the early diplotene and extended to the large growth period to include the bilaminar follicle stage. During the large growth, the rabbit oocytes do not develop to the dictyate or "resting" stage, but remain at the diplotene. At the period preceeding the large growth (the early diplotene) lampbrush chromosomes are revealed made of the central axis 50 nm in diameter wish lateral fibrils. The aggregation of long loosely arranged fibrils makes the chromosome matrix. In the fibrillar zone of the chromosome, numerous roundish granules ca 45 nm in diameter and dense granule accumulations ca 0.15 mkm in diameter were visualized. Large fibrogranular bodies (1--2 mkm in diameter) are seen in association wish chromosomes. All these extra-nuclear bodies that appear on chromosomes differ in their size and pattern. These, likely as the nucleoli, may be considered as morphological expression of the genic activity of lampbrush chromosomes.

[Electron microscopic study of endopolyploid nuclei in rat trophoblast giant cells. III. Nucleolus and its fibrillary center at different stages of the endoreplication cycle]. / Elektronno-mikroskopicheskoe issledovanie éndopoliploidnykh iader v gigantskikh kletkakh trofoblasta krysy. III. Iadryshko i ego fibrilliarnyi tsentr na razlichnykh stadiiakh tsikla éndoreplikatsii.

The fine structure of the nucleolus and nucleolus-forming chromaosomes has been studied in the course of the endomitotic cycle of the trophoblast giant cells on the 12th and 13th days of the foetus development. The nucleolar ultrastructure was regarded in relation to the degree of chromatin condensation in the nucleus. In the nucleus with dispersed chromatin (endointerphase), the nucleoli have the nucleoneme structure and involve the four components: fibro-granular threads and accumulations (with granules 20 nm in diameter), round zones of fibres with moderate electron density surrounded by dense fibrillar material (fibrillar centres), and lacunar spaces. In contact with the nucleolus are thin chromatinous fibres of the karyoplasm which penetrate into the open lacunae on the periphery of the nucleus to be running, presumably, through the whole nucleus. The fibrillar centres either run deep into the lacunar spaces of the nucleolus, or attach to it. In the nuclei with condensed chromtin (endoprophase), the nucleoli are surrounded with a well developed layer of perinucleolar chromatin running along lacunae deep into the nucleolus. The nucleoli here made of the same components as nucleoli in the nuclei with dispersed chromatin, but are the prominent electron dense fibrillar component is getting more obvious, the number of granules in the fibro-granular component is reduced, it lacunae display regions of the nucleolus-organizer not only as fine scattered chromatinous fibres, but also as small compact blocks. A question is discussed of the fibrillar centres of the nucleolus as being places of the nucleolus organizer, and of its changes within the cycle of mitosis and endomitosis.

[Electron microscopic study of endopolyploid nuclei in rat trophoblast giant cells. IV. Changes in nucleolar ultrastructure during cell differentiation]. / Elektronno-mikroskopicheskoe issledovanie éndopoliploidnykh iader v gigantskikh kletkakh trofoblasta krysy. IV. Izmenenie ul'trastruktury iadryshka v khode differentsirovki kletok.

The ultrastructure of the nucleolus of highly differentiated trophoblast giant cells has been studied on the 17th day of the foetus development. Changes in its morphology have been followed in relation to the degree of nuclear chromatin condensation and to the cell differentiation level. The nucleoli have a reticular structure in the nuclei with dispersed and condensed chromatin. In both the cases the nucleoli involve the four components: fibro-granular, fibrillar (of moderate and normal density) and lacunar regions; fibrillar centres are distinguished within the regions. In the nucleoli with condensed chromatin, unlike those with dispersed chromatin, the perinuclear chromatin is clearly seen, and the penetration of nucleolus-organizer threads along lacunae and deep into the nucleolus can be easily followed. The fibrillar centres are more obvious. With the run of a progressive differentiation of the trophoblast cells, the number of granules is reduced; first, the fibro-granular component covers a significant part of the nucleolus, then granules become visible only in the cortical zone of the nucleolus; in the nuclei with strongly condensed chromatin no granules are seen in the nucleolus.

[Fragmentation of polyploid nuclei in rat trophoblast giant cells. II. Formation of deep folds in the nuclear envelope--the beginning of fragmentation]. / Fragmentatsiia poliploidnykh iader v gigantskikh kletkakh trofoblasta krysy. II. Formirovanie glubokikh skladok iadernoi obolochki--nachalo fragmentatsii.

Using light and electron microscopy, the nuclear envelope (NE) of the trophoblast giant cells has been examined at the beginning of the spontaneous fragmentation of nuclei on the last days of pregnancy (not long before their degeneration). In the course of the polyploid nucleus division, deep and narrow invaginations appear in the NE, frequently running through the whole nucleus, from one pole towards the other, and separating it into fragments. Short finger-like outgrowings are seen extending from the long invaginations perperdicularly or at a certain angel. Both the nuclear membrances, having numerous nuclear pores, are involved in the formation of these invaginations and shorter extentions. Local enlargements are seen produced in the perinuclear space, mainly in the area of NE invaginations. Narrow folds, separating the giant nucleus into fragments, are filled with the cytoplasm rich in ribosomes. In the nuclear fragments so produced, association between the earlier dispersed chromatin and the NE becomes stronger. Large accumulations of the condensed chromatin are mainly distributed under the NE, only a few minute chromatin blocks being found in the center of the nucleus filled up with diffuse chromatin.

[Electron microscopic study of the endopolyploid nuclei of the giant cells of the rat trophoblast. I. The ultrastructure of polytene chromosomes and their activity products at different stages of the endoreplicative cycle]. / Elektronno-mikroskopicheskoe issledovanie éndopoliploidnykh iader v gigantskikh kletkakh trofoblasta krysy. I. Ul'trastruktura politennykh khromosom i produktov ikh aktivnosti na raznykh stadiiakh tsikla éndoreplikatsii.

The fine structure of the rat trophoblast giant cell nuclei (on the 12--14th days of the foetus development) has been studied at the two stages of endomitotic cycle--endointerphase and endoprophase. In the endointerphasic nuclei, no large accumulations of condensed chromatin occur, the peripheral chromatin is poorly seen, thin chromatin threads are evenly distributed over the karyoplasm, with their rather clear orientation from the nucleolus towards the nuclear envelope. Among decondensed chromonemes and in association with them, a lot of interchromatinous granules are seen, perichromatinous granules being of a rare occurrence; sometimes small nucleolus-like structures are met. In the endoprophasic nuclei, chromatinous elements are seen as large blocks of condensed chromatin, having various shapes, often elongated, with uneven outlines and zones of decondenced chromatin between them. The peripheral and preinucleolar chromatin is clearly identified. Chromatin blocks near the nucleolus are similar in their size and arrangement to discs of dipterian polytene chromosomes, the interdisc spaces being like the puff zones. The latter are made of loosely arranged fibres 10--20 nm thick and granules 20--30 nm in diametre; part of the puff zones is of fibrillar structure. In the nuclei with condensed chromatin, nucleolus-like fibrillo-granular bodies (1--1.5 mkm) are recognized, in addition to large masses of condensed chromatin with numerous perichromatinuous granules inside and large masses having a comb-honey structure. The revealed morphological differences in structures, formed on endointerphase chromosomes and polytene chromosomes of the endoprophase, may point to the various nature of the products of gene activity produced at different periods of the nuclear cycle.

[Intranuclear and cytoplasmic annulate lamellae in the polyploid giant cells of the trophoblast]. / Vnutriiadernye i tsitoplazmaticheskie poristye plastinki v poliploidnykh gigantskikh kletkakh trofoblasta.

Intranuclear and cytoplasmic annulate lamellae in polyploid giant cells of the trophoblast have been studied in rat placenta on days 12--17 of development. The annulate lamellae are present in the cytoplasm within a limited time, being visible on day 12 only. These are arranged in bundles near the nucleus to be moving then to the cytoplasm. The end parts of annulate lamellae are broadened to make cisterns of rough endoplasmic reticulum. Unlike the cytoplasmic annulate lamellae, those found within the nucleus are seen in part of the nuclei investigated throughout the whole period examined to look as single structures (not gathered in bundles), they can be branching, separating closed spaces within the nucleus (making local swellings in the loci of branching; the latter having electron dense or transparent vesicles). Association with nuclear chromatin in some regions is a peculiar feature of the intranuclear annulate lamellae. This association is especially obvious at endoprophase in the cycle ofthe polytene nucleus during the somatic conjugation--chromonemes unite in a bundle and condense. Ultrastructural changes of the annulate lamellae is noted throughout the polytene nucleus cycle and during the cell differentiation. It is supposed that in the case of temporary labile chromosome polyteny in the nuclear cycle, which is characteristic of mammalian trophoblasts, annulate lamellae can well compare, in their function, with the synaptonemal complex--these prevent from too tight associations of homologues in the course of somatic conjugation of chromosomes.

[Different modes of cell reproduction in the placental differentiation of mammals]. / Razlichnye puti reproduktsii kletok pri differentsirovke platsenty mlekopitaiushchikh.

Summarized is the total evidence on the role of various modes of cell reproduction in the course of differentiation of various trophoblast population cells. The giant trophoblast cells, reaching a tremendously high (for mammals) degree of ploidy (512-4096c), blast cells, reaching a tremendously high for (mammals) degree of ploidy (512-4096c), give an example of cells that display a "non-classical" form of polyteny with not regular polyteny in chromosomes. For the trophoblast cells, a period of easy recognition with not regular, polyteny in chromosomes. For display a "non-classical form of polyteny with not regular polyteny in chromosomes. For the trophoblast cells, a period of easy recognition polytene chromosome has been established timed to definite stages of cell differentiation and of the polytene nucleus cycle. The start of phagocytic activity in trophoblast cells coincides in time with their transition to endoreduplication, both the processes terminating also simultaneously. It does not seem unlikely that such that each a correlation may appear due to a strict programmed appearance of numerous features of trophoblast cells, including their lifespan both in situ and under condition of -transplantation to different organs. Biological importance of various ways of reproduction in trophoblast cells (mitosis, non-completed polyploidizing mitosis, endoreduplication) in various parts of placenta is discussed in relation to their roles in development and functioning of this organo.

[Plication of the nuclear membrane and its derivatives in the polyploid cell nuclei of the rat trophoblast]. / Izuchenie skladchatosti iadernoi obolochki i nekotorykh ee proizvodnykh v iadrakh poliploidnykh kletok trofoblasta krysy.

Folding pattern of the nucleus envelope and intranuclear membrane structures in trophoblast giant cells and in trophoblast of the intermediate region of the rat placenta have been studied. Cells of the intermediate region of the placenta demonstrate deep invaginations resulting in the appearance of lobulated nuclei. Invaginations of the nuclear envelope pass on a narrow fold made by an inner nuclear membrane. The polyploid nuclei of trophoblast giant cells have superficial folds and deeper finger-like invaginations in their envelopes. Such folding trophoblast nuclei in two populations examined are met throughout the whole ontogenesis of the cell. In the giant cells, individual intranuclear tubes or their accumulations are seen. The tubes are made by a unit membrane and are surrounded with a matrix. The nuclear chromatin, diffuse or condenced, is in association with the tube surface. The tubes are met near the nucleolus and on its surface, where these are surrounded with the granular component of the nucleolus. In the trophoblast of the intermediate region of the placenta, intranuclear concentric membranes have been found; made of paired membranes, intramembranous space being filled with electron dense matrix. The concentric membranes lie separately in the karyoplasm, not being associated with the chromatin.

[Fragmentation of polyploid nuclei in the giant cells of the rat trophoblast. I. The ultrastructure of the nuclear fragments]. / Fragmentatsiia poliploidnykh iader v gigantskikh kletkakh trofoblasta krysy. I. Ul'trastruktura iadernykh fregmentov.

Electron microscope study of the nuclear fragments in the rat trophoblast has demonstrated that the division of the trophoblast giant nucleus results first in the formation of a multinuclear cell. Each nuclear fragment is covered with its own nuclear envelope made of two membranes with numerous pore complexes. The chromatin in these nuclear fragments is condenced with various degrees of condensation, which depends on the step of placenta development, cell differentiation and the degree of nuclear fragmentation. The nuclear ultrastructure in nuclear fragments also depends on the degree of nuclear fragmentation and on the level of chromatin condensation. The nucleolus has no granular component. On large fragments, with lower chromatin condensation the nucleolus is not homogenous being made of fragments of more and of less electron dense fibrilles. Small light lacunae are seen in the nucleolus where chromatin threads and strands pass on. With a high chromatin condensation in the nucleus, round small nucleoli look homogenous being made of moderately electron dense fibrilles. Products of chromosome activity have been found in the nuclear fragments: accumulations of minute granules (d = 15--20 nm), perichromatinous granules (d = 35--40 nm), and fibrillar nucleolus-like bodies. In the multinuclear cell, made as the result of fragmentation of the initially giant nucleus, all the small nuclei are first arranged very close to each other, so that the contours of the neighbouring nuclei coincide.

[A quantitative study of Ag-positive nucleolar segments revealed by silver staining in the interphase nuclei of trophoblast cells from the rat placental connective zone]. / Kolichestvennoe izuchenie Ag-polozhitel'nykh uchastkov iadryshek, vyiavliaemykh v interfaznykh iadrakh kletok trofoblasta soedinitel'noi platsenty krysy metodom serebreniia.

A cytomorphological study was made of silver stained nucleoli in interphasic nuclei of trophoblast cells from the rat placenta connective zone, in addition to calculation of Ag-positive spherules in the nucleoli. The prevalent number of Ag-positive nucleolar spherules in the nuclei was 6, corresponding to the number of nucleolar organizers (NOR's) in the diploid chromosome complement of the rat. The mean number of Ag-positive spherules in the nucleoli progressively increase in the course of polyploidization from 2c to 32c; variability of the spherule number also increasing. The mean area of nucleoli is found to increase in proportion to the ploidy degree. A high correlation is found between the number of Ag-positive spherules and the area of nucleoli in the nucleus (r = 0.78). This appropriateness is exhibited at all the ploidy levels. The number of Ag-spherules and the area of nucleoli are found to depend slightly on the number of nucleoli. The possibility to use the number of Ag-positive spherules as a criterion of the activity of the NOR in interphasic nuclei is discussed.

[Ultrastructural features of the nucleus and cytoplasm of rat trophoblast cells of the connective zone of the placenta and labyrinth]. / Osobennosti ul'trastruktury iadra i tsitoplazmy kletok trofoblasta soedinitel'noi zony platsenty i labirinta krysy.

Ultrastructural organization of the rat trophoblast cells in the connective zone of placenta and labyrinth was investigated on the 12-14th days of gestation. A clear distinction was revealed in the cytoplasm ultrastructure of two cell subpopulations within the connective zone of placenta, i.e. glycogen and trophospongium cells. The former display a well defined network of long thin channels of granular endoplasmic reticulum situated mainly around the glycogen clusters. On the contrary, the latter are rich in the smooth endoplasmic reticulum but lacking glycogen accumulation. Differences in the nucleolar ultrastructure in these two cell subpopulations are not very considerable. A characteristic feature of glycogen cells is the presence of numerous round or oval small-fibrillar nucleolus-like bodies with the diameter of granules 20 nm. The trophoblast cells of the labyrinth are heavily laden with polysomes, which sometimes attach to short channels of the granular endoplasmic reticulum. Not often there occur short profiles of the agranular endoplasmic reticulum. Nucleolus-like bodies are found in all the cell types examined. This means that the nucleolus-like bodies may arise not only on the lampbrush chromosomes in the oocytes or polytene chromosomes, but also in the somatic cells which are capable of dividing mitotically.

[A comparative study of the main components of the nucleolus in different populations of rat trophoblast cells during differentiation. I. The nucleoli of the trophoblast cells in the labyrinth section of the placenta]. / Sravnitel'noe izuchenie osnovnykh komponentov iadryshka v raznykh populiatsiiakh kletok trofoblasta krysy v khode differentsirovki. I. Iadryshki kletok trofoblasta labirintnogo otdela platsenty.

The nucleolus undergoes some steps of structural transformation during differentiation of the labyrinth trophoblast cells. Primarily (on day 13 of gestation) the nucleolar components become rather disjoined. The nucleolus is composed of a loose net of strands of granulofibrillar and dense fibrillar components bearing fibrillar centers (FCs). Strands are separated by large lacunae. This rare-occurring type of nucleoli is replaced on the next (14th) day by the nucleolonemal type and later--by the compact nucleolar type. FCs with dense fibrillar component strands become extended into the masses of granulofibrillar component. Such transformations of nucleolar structure seem to be an expression of a fast-proceeding differentiation of the labyrinth trophoblast cells.

[A comparative study of the main components of the nucleolus in different populations of rat trophoblast cells during differentiation. II. The nucleoli of the trophospongium cells, the glycogen cells and the secondary giant cells]. / Sravnitel'noe izuchenie osnovnykh komponentov iadryshka v raznykh populiatsiiakh kletok trofoblasta krysy v khode differentsirovki. II. Iadryshki kletok trofospongiuma, glikogenovykh kletok i vtorichnykh gigantskikh kletok.

A comparative study was performed of the arrangement of different nucleolar components during differentiation of trophoblast cell populations in the junctional zone of placenta (glycogen cells and trophospongium) and in the secondary giant cells. Each cell type is characterized by specific interrelation of nucleolar components. Some glycogen cells show signs of segregation of nucleolar components: strands of nucleolar components with fibrillar centers (FCs) are displaced to the periphery of the nucleolus and contact with the perinucleolar chromatin. Large reticular nucleoli in trophospongium cells contain many FCs which are gathered into several "chains" by strands of dense fibrillar component. Such a "chain" has also been found in nucleoli of secondary giant cells, with greater number of FCs in each "chain". Relationship between the arrangement of nucleolar components and the level of cell differentiation is discussed.

[A study of the polyploid nuclei of the giant trophoblast cells of several species of rodents using phase contrast microscopy]. / Izuchenie poliploidnykh iader gigantskikh kletok trofoblasta nekotorykh vidov gryzunov s pomoshch'iu fazovokontrastnoi mikroskopii

Patterns of chromosome morphology in high polyploid trophoblast nuclei of placenta were compared in the rat, rabbit and Microtus arvalis. In the rat and rabbit placenta two types of nuclei were recognized. Some nuclei have ribbon-like chromosomes, while others display thin oligotene fibrils with paired chromomers evenly distributed throughout all karyoplasm. In the latter case, the polytenic structure of chromosomes is seen preserved only near the nucleoli. In the rat and rabbit trophoblast nuclei, the ribbon-like polytene chromosomes could be distinguished only with phase contrast microscopy. In the trophoblast nuclei of Microtus arvalis polytene chromosomes were found only at early stages of embryonic development (9 day old embryo). On later stages of cell differentiation, the chromosomes or chromosome rosetts are seen. Similarities in mechanisms of polyploidization in the high polyploid nuclei of Diptera and in trophoblast nuclei of rodents are discussed.

[Comparative study of normal and degenerating oocytes in the golden hamster in the early stages of postnatal development. Polyovular follicules and multinuclear oocytes]. / Sravnitel'noe issledovanie normal'nykh i degeneriruiushchikh ootsitov zolotistogo komiachka v nachale postnatal'nogo razvitiia. Poliovuliarnye follikuly i mnogoiadernye ootsity.

Oocyte atresia in the golden hamster ovarium was followed at successive stages of the postnatal development, from a 5th to a 40th day. Oocyte degeneration may occur in various ways: by formation of so to say Z cells (in the pachynema stage oocytes) or by nuclear pycknosis (in the pachynema and diplonema stage oocytes, and after ovarial follicles formation - at the stage of primordial and one-layered follicle). In growing ovarial follicles, the degeneration begins from the picnosis of follicular cell nuclei, or changes in zona lucida. The oocyte nucleus is not pycknosized, but undergoes series of rearrangement quicker, than in the norm, and is able to enter into meiotic divisions I and II. A mass degeneration is followed in golden hamster oocytes at the pachynema stage, being then much reduced due, probably, to a slower process of atresia in ovarial follicles. Two-or tree-nucleated oocytes with a far developed degeneration are observed. A comparative study of uni- and polyovular follicles at progessive stages of ovarium development in juvenile females has shown that the follicles develop synchronously. Unlike occytes of uniovular follicles, all the oocytes of polyovular follicles enter into the large growth period from the beginning of their formation.