Ultrastructural changes and programmed cell death of trophocytes in the gonad of Isohypsibius granulifer granulifer Thulin, 1928 (Tardigrada,Eutardigrada, Isohypsibiidae)

The studies on the fates of the trophocytes, the apoptosis and autophagy in the gonad of Isohypsibius granulifer granulifer have been described using transmission electron microscope, light and fluorescent microscopes. The results presented here are the first that are connected with the cell death of nurse cells in the gonad of tardigrades. However, here we complete the results presented by Węglarska (1987).The reproductive system of I. g. granulifer contains a single sack-like hermaphroditic gonad and a single gonoduct. The gonad is composed of three parts: a germarium filled with proliferating germ cells (oogonia); a vitellarium that has clusters of female germ cells (the region of oocytes development); and a male part filled with male germ cells in which the sperm cells develop. The trophocytes (nurse cells) show distinct alterations during all of the stages of oogenesis: previtello-, vitello- and choriogenesis. During previtellogenesis the female germ cells situated in the vitellarium are connected by cytoplasmic bridges, and form clusters of cells. No ultrastructural differences appear among the germ cells in a cluster during this stage of oogenesis. In early vitellogenesis, the cells in each cluster start to grow and numerous organelles gradually accumulate in their cytoplasm. However, at the beginning of the middle of vitellogenesis, one cell in each cluster starts to grow in order to differentiate into oocyte, while the remaining cells are trophocytes. Eventually, the cytoplasmic bridges between the oocyte and trophocytes disappear. Autophagosomes also appear in the cytoplasm of nurse cells together with many degenerating organelles. The cytoplasm starts to shrink, which causes the degeneration of the cytoplasmic bridges between trophocytes. Apoptosis begins when the cytoplasm of these cells is full of autophagosomes/autolysosomes and causes their death.     

沙蚕科的性成熟及精卵发生

就沙蚕性成熟的调控机制、性信息素以及卵子发生、精子发生等方面进行了综述.关于性成熟的调控机制,分别从激素和M期的促进因子（MPF）来讨论沙蚕的性成熟的调控机制,目前认为激素对沙蚕性成熟具有重要影响,而且发育早期影响比较明显,而MPF则通过调控减数分裂来影响性成熟.沙蚕性信息素具有性别辨认和群浮同步性的作用,文中讨论了性信息素的主要成份以及功能.对于精卵的研究,分别就卵子发生、精子发生以及油细胞在卵子发生和精子发生中的作用来探讨沙蚕中的研究概况,通过已有的资料,综述精卵发生细胞学及显微结构.