Boshnakova, E.

Marinova, Tz.

English

Varna Medical University Press: Journals

SOME U L T R A S T R U C T U R A L P E C U L I A R I T I E S OF T H E N U C L E I OF THYMUS E P I T H E L I A L C E L L S Tz. Marinova, E . Boshnakova Thymus humoral factors wi th exclusively important biological ac t iv i ty are synthesized in thymus epithelial cells. Tha t is why these cells have been always the object of numerous investigations. However, as a matter of fact, there are no certain data of their cytological bases and functional ac t iv i ty . Thorough study of the fine structure of epithelial cells (including their nuclei) is obligatory for the detailed histological analysis . U n t i l now we have ul tra-structural information only for the size, form and number (10, 11, 13, 14, 17). Therefore, our investigation aims further study by electron-microscope tech-nique. Material and methods Thymus particles taken of 13 ki l led four-month old conventional mice (Swiss-race) were prepared for electron-microscope study by using the standard method: prefixation in 5% glutaraldehyde, postfixation in 1% osmium tetra-oxide, dehydration in ascendant alcohols and incorporation in Durcupan A C M . Double contrast wi th uranyl acetate and plumbum nitrate was applied to ultra thin cuts. Electron-microscope J E M 7 A was used in our study. Results and discussion Nuclei of epithelial cells from the three regions of a thymus lobe (core, cortico-medullar and medulla) were investigated. A l l of them possess certain common features. Their size is relat ively large. The form is usually irregular: star-like in cortical epithelial cells or rounded and ellipse in medullar cells. One cell possesses (as a rule) one nucleus. The light (shining) appearance of the nucleus is due to the dispersed chromatin (euchromatin) in greater number of epithelial cells, whereas the compact chromatin (heterochromatin) is a scantily located thin layer-stripe near to the inner surface of nuclear membrane. Considerable electron-microscope differences are registered simultaneously wi th the aforementioned ones, mainly refering to the characteristics of some non-chromatin nuclear structures, outlines and width of perinuclear space. Thei r combination makes us suggest 2 basic groups of nuclei . F i r s t group nuclei are: w i th 1 or more reticular spotted nucleoli showing wel l outlined f ibr i l lar and granular components (fig. l a , l b ) . They have as an exception nucleoli wi th variable morphology (compact and ret icular) . Nuclear bodies (sphere-l ike) are often detected. They are scarce inordered fibriles surrounded by a halo. Some of them are just near to the nucleolus and connected to the peri-nuclear chromatin. More rare the special components of the nuclear corpuscles are grouped in a definite order. The nuclear membrane of some epithelial cells forms surface or deeper invaginations. The perinuclear space is wider and communicates wi th broad cisterns of granular endoplasmatic ret iculum. The Some ultrastructural peculiarities of the nuclei of thymus. 21 Fig. 1-b: Part of reticular and mixed-type (compact and reticular) nucleolus 22 Tz. Marinova, Е. Boshnakova latter involve greater part of cytoplasma, often possess electron-lighter homo­geneous content and neighbour many polysomes, mitochondria, we l l formed and developed Goldj i apparatus, etc. The nuclei from the second group are characterized wi th the single or nu­merous compact temporary (between compact and reticular) nucleoli wi th rounded or irregular form. More rare single nuclear corpuscles are found sometimes. The nuclear contours are usually smooth. Perinu­clear space shows no deviation; it is combi­ned w i t h narrow cisterns of granular endo-plasmatic reticulum, vacuollar and wel l form­ed Goldj i complex, excess of mitochondria and secondary lysosomes. The variety of va-r£ W % *j cuollas and the present intracellular cysts is Щ the possible reason of eccentric nuclear loca-W tion in these cells. " > ф ^ More rare but interesting findings in a l l three zones were: nuclei wi th prevailing dis-X* ^ S K persed chromatin and compact or ring-like . f t nucleolus; nuclei of epithelial cells in mi­tosis; binuclear epithelial cells (fig. 2); nu-* clear incorporations l ike myelo-formations wi th no nuclear membrane. Our results show that the nuclei of epi-Fig. 2: Part of bi-nuciear epithe- thelial cells in every zone of the thymus have Hal cell common ultrastructural features: they are single, large and light. These peculiarities are s imilar to those establiched by other authors (10, 11, 13, 14, 17) and support the differentiation of epithelial cells apart from mesenchymal reticular and lymphoidal cells. We also established some other regional fea­tures concerning most of a l l nuclear form. The different form corresponds to the total construction of the cell reticulum formed by epithelial cells in the core and medulla of the thymus lobe. Certain interest arouses the presence of some peculiarities in the fine structure of the nuclei whose combination, s imilar in a l l three regions of the thymus, is an important key to the question of the functional ac t iv i ty of epi­thelial cells. Thus , the nuclei of first group show a homogeneously dispersed chromatin combined wi th a presence of a reticular nucleolus, also often several nuclear corpuscles in a microscope cut (the morphology is related to type I or «simple» nuclear corpuscles after Dupuy-Coin, A . M . and M . B o u t e i l l e — 1972), widened perinuclear space and nuclear invaginations. The combination of these features is regarded to a certain 'cytologic sign of nuclear ac t iv i ty ( 1 , 7, 8) and due to the exclusively developed granular endoplasmatic reticu­lum and excess of other cell organels it shows an intensive protein synthesis, mainly for a cell export ( 1 , 2, 3, 6, 7, 15). These data, together wi th the fact that a l l thymus humoral factors are most of a l l wi th protein origin (5), makes us suggest that epithelial cells of the three regions (zones) of the thymus are engaged (involved) in the synthesis of thymus factors. However, the finely dispersed chromatin in the eccentrically located in the cell nuclei of second group, together wi th the excess of vesicullar structures and intracellular cysts Some ultrastructural peculiarities of the nuclei of thymus. 23 in cytoplasma (objects of our previous investigations — 4, 12) support the idea of their participation in the synthesis of products wi th non-protein origin (mucopolysaccharides). The prevail ing condensed chromatin and the presence of r ing-like or compact nucleolus are signs of low or even absent functional ac t iv i ty (2, 3) . The same features established in our present study indicate that small number of epithelial cells do not take part or are not s t i l l involved in the synthesis of thymus factors. The mitotic ac t iv i ty 'o f certain epithelial cells is also interesting concern­ing the opinion of S . Marie (1964): by mitosis there is a possibility to restore the number of degenerated epithelial cells incorporated in Hassa l i i corpuscles ( in medulla) or of transformed epithelial ( in lymphoid) cells ( in core). J . Scheiff (1976) reports multinuclear epithelial cells in preparations of mice. According to him the increase in number of the nuclei relates to the age involution of thymus which requires further our investigations of mice Swiss concerning age. The established and reported peculiarities of the fine structure of nuclei support and prove our previous conclusions for a definite morphological hetero-genicity of thymus epithelial cells being the base of their various functional a c t i v i t y . R E F E R E N C E S 1. В а с и л е в , H. Б. Ядрени нехроматинови структури при реактивни и ту-морни процеси в лимфните възли (Електр.-микроск. изсл.), Канд. дисерт., София, 1977. — 2. В ъ л к о в, И в . Патология на лимфните възли. С , Мед. и физк., 1975, 233. — 3. В ъ л к о в, И в . Експериментална медицина и морфология, 1975, 2, 65—74. —• 4. М а р и н о в а , Ц., Е. Б о ш н а к о в а . Микробиологични проблеми, 7, 1979, 9—16. — 5. П е т р о в, Р. В. — Имунология и имуногенетика. С , Мед. и физк., 1978, 298. — 6. Х р и с т о л ю б о в а , Н. Б. Функциональная морфология цитоплазмати-ческих органелл. Новосибирск, Наука, 1977, 188. — 7. A n d r e , J . Problems d'ultra-structures et de functions nucleares. Paris, Mass. & Cie, 1959, 221. — 8. D u p u y - C o i n , A. M. е t a 1. / . Ultrastr. Res., 38, 1972, 174—187. — 9. D u p u y - C o i n , A. M., M. В о u t е i 1 1 e. J. Ultrastr. Res., 40, 1972, 55. — 10. G a г а с i , Е. е t a 1. Cli­nical immunology and immunopathology, 11, 1978, 157—167. — 11. M a n d е 1, Т. Austr-J. Exp. Biol. Med. Sci., 47, 1969, 153—155. — 12. M а г i n о v a, T z., E . В о s h n a -k o v a . Scr. Sci. Med., Sof., 16, 1979, 37—42. — 13. О 1 a h, L . , P. R 6 h 1 i с h, I . Т о г о . Ultrastructure of lymphoid organs. Budapest, Akad. Kiado, 1975 (atlas). — 14. P е r е i r a, G . , I . C l e r m o n t . Anat. Res., 169, 1971, 613—626. — 15. R e d ­m a n , С. M., M. G . С h е r i a n. / . Cell. Biol., 52, 2, 1972, 231—245. — 16. S a i n -t e - M a r i e , G . , C. P. L е b 1 о n d. Blood, 23, 1964, 275—299. — 17. S с h е i f f. J . M. / . M. Cell. Tiss. Res., 170, 1976, 305—314. Tz. Marinova, Е. Boshnakova Н Е К О Т О Р Ы Е ОСОБЕННОСТИ У Л Ь Т Р А С Т Р У К Т У Р Н О Й Х А Р А К Т Е Р И С Т И К И Я Д Е Р Э П И Т Е Л Ь Н Ы Х К Л Е Т О К В И Л О Ч К О В О Й Ж Е Л Е З Ы Ц. Маринова, Е. Бошнакова Р Е З Ю М Е Исследована тонкая структура ядер эпительных клеток вилочковой железы 13 че­тырехмесячных мышей породы Swiss, забитых посредством декапитации. Описаны уль­траструктурные характеристики, общие для всех ядер. Наряду с ними обноружены и определенные различия в тонкой структуре ядер эпительных клеток, принадлежащих к различным областям вилочковой дольки, с одной стороны, и к одной и той же области, с другой. Эти различия связаны главным образом с формой ядра, характеристикой не­которых из нехроматиновых ядерных структур, ядерным контуром, а так же и с широ­той перинуклеарного пространства. Установлена закономерность в сочетании особен­ностей тонкой структуры ядра и цитоплазмы, которая связана с функциональной актив­ностью эпительных клеток. 

SOME ULTRASTRUCTURAL PECULIARITIES OF THE NUCLEI OF THYMUS EPITHELIAL CELLS

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SOME ULTRASTRUCTURAL PECULIARITIES OF THE NUCLEI OF THYMUS EPITHELIAL CELLS

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