Morphofunctional transformations of the yolk syncytial layer during zebrafish development

Abstract

The yolk syncytial layer (YSL) is a provisory extraembryonic structure of teleost fishes and representatives of some other taxa with meroblastic cleavage. The YSL of teleosts is a symplast with polymorphous polyploid nuclei. It is known to perform nutritional, morphogenetic, immune, and, probably, other functions. Data about the YSL organization, functioning and regulation is fragmentary. Although gene expression patterns and other aspects of YSL functioning have been studied in Danio rerio, the morphology of its YSL has not been described in detail. The study of zebrafish YSL structure on sequential developmental stages is necessary to recognize specific features of this important polyfunctional system in this model organism and to extend our knowledge about provisory systems. The thickness of the YSL and the distribution of its nuclei are not uniform on each stage and change during development. During oblong and sphere stages the internal YSL (I-YSL) is filled with yolk inclusions; interphase yolk syncytial nuclei (YSN) and mitotic asters can be seen. During doming and epiboly the external YSL (E-YSL) is thicker than I-YSL. On the subsequent stages the YSL is thickened caudally. The dorsal YSL part is thickened during early segmentation stages and becomes the thinnest YSL region later. The anterior part of the YSL is thin, but enlarges during larval period. The YSN of different size and diverse forms, from regular to lobed, are present and form clusters. The number of irregular-shaped nuclei increases during development. The YSL thickens in the end of endotrophic and in the course of endo-exotrophic period, and its cytoplasm contains numerous yolk inclusions. After yolk exhaustion the YSL is flat. As the YSL degrades, the YSN become pycnotic, and the YSL remnant probably is cleared by phagocytes.

When bigger is better: the role of polyploidy in organogenesis

“…This layer contains syncytial nuclei that become polyploid as gastrulation proceeds, a frequent property of yolk nuclei [37]. Although the function of increased ploidy within the yolk nuclei has yet to be evaluated, given the role that the yolk appears to play in the morphological movements associated with epiboly and gastrulation, it will be interesting to explore if the size of nuclei influences these events.…”

Structure of the yolk syncytial layer in Teleostei and analogous structures in animals of the meroblastic type of development

“…7d and 8a. The apop tosis features were observed in the YSL of the zebrafish only after the yolk deposits disappeared (Kondakova and Efremov, 2014a). We propose that the remnants of the YSL and the apoptotic bodies are utilized by the phagocytes in both species studied (Fig.…”

“…6a-6c). The distributional pattern of the YSN of the zebrafish was described earlier (Kondakova and Efremov, 2014a). The groups of the YSN are visible in the anterior and caudal areas (Figs.…”

Морфологические особенности черноморского калкана (Scophthalmus maeoticus) в период эмбрионального развития

“…В данном описании эмбриогенеза калкана мы придерживаемся терминологии и интервалов развития (оплодотворение, дробление, бластуляция, гаструляция, органогенез, начало мышечной моторики и подготовка к вылуплению) согласно приведённым в работе Махотина [7]. В связи с тем, что описание развития эмбриональных структур калкана рассматривали в диапазоне оптимальных температур +14…+16°C, при которых длительность разных этапов значимо отличается, хронология появления и трансформации морфологических структур в процессе эмбриогенеза калкана приведена в относительных единицах (относительном возрасте эмбриона в процентах от общей продолжительности эмбриогенеза, % RT) [22], аналогично безразмерной характеристике τ 0 [7].…”

“…Перибласт становится симпластом (тканью, характеризующейся отсутствием границ между клетками и расположением ядер в сплошной цитоплазме) непрерывной системы протопластов, связанных плазмодесмами и ограниченных клеточной стенкой с полиморфными полиплоидными ядрами [22]. Перибласт контролирует эпиболию, структурирование, спецификацию клеток и морфогенез слоёв зародыша в процессе гаструляции.…”