MAST CELLS OF LYMPH HEARTS DURING ONTOGENESIS OF FROGS RANA TEMPORARIA
M. I. Krylova
Institute of Cytology RAS, St. Petersburg;
e-mail: heartdev@mail.cytspb.rssi.ru
Electron microscopic observations of the lymph hearts of tadpoles and yearling frogs of Rana temporaria
showed that mast cells (MCs) were present not only between muscle fibers (population of resident MCs), but in
the cavities of lymph heart (population of circulating MCs), too. There were some differences in the ultrastructure
of the resident MCs at each studied stage of larval development. The first recognizable MCs were revealed
in the lymph hearts at premetamorphosis (stages 39—41). MCs presented as mononuclear relatively small and
slightly elongated cells with a few immature secretory granules and numerous free ribosomes, polysomes and
short cisternae of rough endoplasmic reticulum (RER) in the cytoplasm. Chromatin of their nuclei was poorly
condensed; the Golgi apparatus was moderately developed. At pro-metamorphosis (stages 44—45), we revealed
MCs at different levels of their differentiation. Some MCs demonstrated an active process of granulogenesis in
their cytoplasm. Among densely packed cytoplasmic organelles, immature secretory granules were closely associated
with cisternae of RER and free ribosomes. Other MCs appeared as more differentiated cells. They were
characterized by a predominantly heterochromatic nuclei and cytoplasm filled with polymorphic and heterogeneous
granules. MCs also showed a reduction in the number of free ribosomes and cisternae of RER in the cytoplasm.
On the contrary, the Golgi apparatus was well developed. Stacks of Golgi cisternae, detaching vacuoles,
and progranules occupied the perinuclear region. The majority of the outlines above ultrastructural features
of differentiated MCs were typical for MCs of yearling frogs. At metamorphic climax (stages 52—53), MCs often
tightly contacted with macrophages. We did not reveal apoptotic MCs. However, some MCs exhibited morphological
features typical for programmed necrosis-like death, which was characterized by mitochondria swelling,
dilatation of cisternae of RER and nuclear envelope, plasma membrane rupture and subsequent loss of intracellular
contents. Electron microscopical immunocytochemistry revealed the localization of atrial natriuretic
peptide (ANP), substance S (SP) and heat shock protein (Hsp70) in the secretory granules of the resident and
circulating MCs at different stages of tadpole development and in yearling frogs.
Key words: resident and circulating mast cells, development, ANP, SP, Hsp70, immunolocalization,
lymph heart, frog
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