A unique mechanism of nuclear division in Giardia lamblia involves components of the ventral disk and the nuclear envelope

The fine structure of the binucleate, parasitic protist Giardia lamblia during interphase and divisional stages was studied by serial thin sectioning and three-dimensional reconstructions. The earlier sign of nuclear division is the development of a few peripheral areas of densely packed chromatin directly attached to the inner nuclear envelope. An intracytoplasmic sheet of ventral disk components grows from the cell periphery towards one of the nuclei, apparently constricting this nucleus, which becomes located at a ventral bulge. After the basal bodies become duplicated, a full nuclear division occurs in trophozoites, giving two pairs of parent-daughter nuclei. This full division occurs in a dorsal-ventral direction, with the resulting nuclear pairs located at the sides of the two sets of basal bodies. A new ventral disk is formed from the disk-derived sheets in the cell harboring the four nuclei. Cytokinesis is polymorphic, but at early stages is dorsal-to-dorsal. Encysting trophozoites show the development of Golgi cisternae stacks and dense, specific secretory granules. 3-D reconstructions show that cysts contain a single pair of incompletely strangled nuclei. The dividing Giardia lacks a typical, microtubular spindle either inside or outside the nuclei. The nuclear envelope seems to be the only structure involved in the final division of the parent-daughter nuclei.

Ultrastructural study of rabbit metrial gland

An ultrastructural study has been made of the rabbit metrial gland in an attempt to identify the nature and the possible function of this gland. Six pregnant rabbits were used in this work at 15, 20 and 27 days of pregnancy. Two-types of cells were identified, granulated and fibroblast-like stromal cells. They differ from each other by the presence of the granules and paleer staining cytoplasm of the former. By the end of pregnancy phagocytic activities of the granulated cells were noticed

Estudo morfológico, morfométrico, topoquímico subcelular e em réplicas de criofratura da célula acinosa pancreática do rato durante a vida fetal / Morphological, morphometric, subcellular topochemical and freeze-fracture studies of the rat pancreatic acinar cell during the fetal life

A diferenciaçäo morfológica terminal das células acinosas pancreáticas do rato, durante o desenvolvimento fetal, foi estudada morfometricamente em cortes semi-finos e ultra-finos. As modificaçöes morfométricas observadas nas estruturas intra-celulares e no plasmalema baso-lateral e luminal, foram monitoradas por estudos morfológicos qualitativos, topoquímicos subcelulares e de réplicas de criofratura. A massa pancreática no período estudado de 18 e 22 dias de vida pré-natal, exibiu um crescimento exponencial (Y = 0,00004 e 0,60x), com um tempo de duplicaçäo T= 1,15 dias. A análise morfométrica mostrou que durante o processo de diferenciaçäo, as células acinosas aumentam substancialmente o seu volume citoplasmático (com um incremento de 1.316 por cento, entre os dias 19 e 22). Este aumento de volume citoplasmático, ocorre principalmente devido ao exuberante acúmulo de gräos de zimogênio. O volume e superfície totais dessas estruturas intracelulares, crescem, respectivamente, de 410,5 por cento e 1.400 por cento, durante o intervalo evolutivo de 18 a 22 dias de vida pré-natal. A análise gráfica mostrou que os crescimentos volumétrico, superficial e numérico dos gräos de zimogênio, säo todos do tipo exponencial. A comparaçäo da evoluçäo dos diferentes parâmetros morfométricos dos gräos de zimogênio, sugere que durante o desenvolvimento, grânulos de zimogênio pré-existentes aumentam o seu tamanho individual. O volume e superfície totais do retículo endoplasmático granular (REG), também aumentam significantemente, principalmente no período de 19 a 21 dias de vida gestacional, quando crescem, respectivamente, de 156,4 por cento e 147,5 por cento...