Ультраструктура необластов у турбеллярии Geocentrophora wagini Timoshkin, 1984 (Lecithoepitheliata: Plathelminthes)

И.М. Дробышева

Труды Зоологического института РАН, 2016, 320(2): 176–192 · https://doi.org/10.31610/trudyzin/2016.320.2.176

Резюме

Ацеломорфа и плоские черви (Acoelomorpha и Plathelminthes) обладают уникальной системой стволовых клеток – необластов, которые, как полагают, составляют единый пролиферативный компартмент для соматических клеток и клеток зародышевой линии. Между тем на электронно-микроскопическом уровне эти клетки остаются не изученными в большинстве таксонов ресничных червей. В этой работе описывается ультраструктура необластов у турбеллярии из таксона Lecithoepitheliata (Plathelminthes): байкальского эндемика Geocentrophora wagini Timoshkin, 1984. Необластоподобные клетки G. wagini определяются высоким ядерно-цитоплазматическим соотношением. Цитоплазма обнаруживает черты недифференцированных клеток: она содержит свободные рибосомы и митохондрии, тогда как другие органеллы редки и встречаются не во всех необластах. На основании цитоплазматической и ядерной организации в паренхиме выделены три основных типа необластов. В типе 1 ядра имеют сложную, разветвленно-отростчатую конфигурацию. Периферический гетерохроматин не выражен. В цитоплазме встречается крупная рыхлая структура фиброзной природы, а также миниатюрный аппарат Гольджи с несколькими секреторными гранулами. Ядра необластов типа 2, несмотря на отдельные выросты или инвагинации, имеют более простые и обычные контуры, чем таковые типа 1. Наблюдается слабое развитие периферического конденсированного хроматина, а плотность распределения отдельных сгустков гетерохроматина по всему пространству ядра обычно выше по сравнению с типом 1. Вблизи оболочки ядра со стороны цитоплазмы иногда можно видеть кластер мелких плотных гранул или небольшое рыхлое тельце. Для необластов типа 3 характерны наиболее компактные ядра с гетерохроматином в виде крупных неправильных блоков предельно высокой электронной плотности. Многие из этих блоков соединяются друг с другом и с мембраной ядра. Скудная цитоплазма содержит только митохондрии и рибосомы. Недифференцированные клетки в гастродермисе демонстрируют сходство с необластами типа 2 в паренхиме. Впервые за пределами Tricladida в цитоплазме необластов отмечены особые структуры: рыхлые фиброзные тельца и кластеры гранул, которые, вероятно, могут быть функционально тождественны хроматоидным тельцам планарий. Полученные результаты вносят свой вклад в сравнительную морфологию стволовых клеток у плоских червей и базовых Bilateria и подтверждают гетерогенность пролиферативного компартмента у турбеллярий.

Ключевые слова

Lecithoepitheliata, Plathelminthes, стволовые клетки

Поступила в редакцию 14 июля 2015 г. · Принята в печать 4 марта 2016 г. · Опубликована 24 июня 2016 г.

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