Ultrastructural aspects of the intercellular bridges between female bee germ cells

Abstract

The germline cells in the ovary of the female bee are interconnected by intercellular bridges kept open by cytoskeletal reinforcements in the plasmic membrane. These bridges among the germline cells display a dynamic behavior and probably act in the determination of the oocyte among the cells of the clone formed by the premeiotic mitoses, subsequently forming a pathway that enables the products synthesized by the nurse cells to reach the oocyte during its maturation. The cytoskeletal elements in the intercellular bridges of bee gonads are basically microfilaments and microtubules, but another type of filament (thick, of non-defined nature, associated with elements of the endoplasmic reticulum) is present in the bridges between the premeiotic cystocytes. This filament crosses the bridge, using microfilaments to fasten itself to the plasmic membrane. These filaments appear to control the span of the bridge. Upon completion of the proliferation phase the cystocytes take on a rosette shape, and a fusome formed by the convergence of the bridges appears at their center. The thick filaments are not present in this conformation. The differentiation of the oocyte and the nurse cells leads to a new change, in which the bridges are reoriented to convey the content of the future nurse cells to the oocyte.Keywords: nurse cells, cyst, cytoskeleton, oocyte. RESUMO Aspectos ultra-estruturais das pontes intercelulares entre as células germinativas das fêmeas de abelhasNo ovário das abelhas as células germinativas e as células foliculares são interconectadas por pontes intercelulares mantidas abertas por reforços do citoesqueleto na membrana plasmática. As pontes entre as células germinativas têm comportamento dinâmico e provavelmente atuam na determinação do ovócito entre as células do clone formado pelas mitoses pré meióticas formando posteriormente uma via de transporte para que os produtos sintetizados pelas células nutridoras atinjam o ovócito durante sua maturação. Os elementos do citoesqueleto presentes nas pontes intercelulares das gônadas das abelhas são basicamente microfilamentos e microtúbulos, mas nas pontes entre os cistócitos pré-meióticos outro tipo de filamento (espesso de natureza não definida, associado a elementos do retículo endoplasmático) está presente, atravessando a ponte e prendendo-se através dos microfilamentos à membrana plasmática. Estes filamentos aparentemente controlam o vão da ponte. Terminada a fase de proliferação os cistócitos tomam a forma de uma roseta e um fusoma, formado pela convergência das pontes, aparece no centro desta. Nesta conformação os filamentos grossos não estão presentes. Nova mudança ocorre com a diferenciação do ovócito e das células nutridoras, com a reorientação de todas as pontes de maneira a canalizar o conteúdo das futuras células nutridoras para o ovócito.Palavras-chave: célula nutridora, cisto, citoesqueleto, ovócito. 310 PATRÍCIO, K. and CRUZ-LANDIM, C.

Cytoskeletal organization of bee ovarian follicles during oogenesis

“…Again, this location is consistent with the sites where ultrastructural studies have found the presence of microtubules (Patrício and Cruz-Landim, 2006;Staurengo-da-Cunha, 1988). The RNA that passes from the nucleus into the nurse cell cytoplasm through the nuclear pore and from one nurse cell the another until reach the oocyte.…”

“…The tubulin in the bridges may be the remains of mitotic spindle and therefore located in the fusome, as has been revealed in transmission electron microscopy images (Patrício and Cruz-Landim, 2006). Impaired development of fusome hinders oocyte growth (Cuevas et al, 1996;Hartfeler and Steinbück, 1997;Patrício and Cruz-Landim, 2006;Tanaka and Hartfelder, 2004).…”

“…Its distribution in the germarium suggests a main role as a mechanical component of cytoskeleton that keeps open the intercellular bridges forming the so-called ring canals (Cassidy and King, 1969;King et al, 1982;Theurkauf and Hazelrigg, 1998), thus allowing for the transfer of substances among the cystocytes. Although the main role of actin in this part of the ovariole is structural, Patrício and Cruz-Landim (2006) suggested an additional function concerning the motility needed for cystocyte rearrangements in the cyst during oocyte differentiation. In the vitellarium, F-actin was observed mostly in follicles of early vitellogenic oocytes with a characteristic distribution in each type of cell.…”

“…The tubulin in the bridges may be the remains of mitotic spindle and therefore located in the fusome, as has been revealed in transmission electron microscopy images (Patrício and Cruz-Landim, 2006). Impaired development of fusome hinders oocyte growth (Cuevas et al, 1996;Hartfeler and Steinbück, 1997;Patrício and Cruz-Landim, 2006;Tanaka and Hartfelder, 2004). The role of the circulation of substances among cystocytes, as well the direction of their flow, is essential in determining which cystocyte will become the oocyte (Büning, 1994;Cuevas et al, 1996;Telfer, 1975;Theurkauf et al, 1992).…”

“…Accordingly, in the bee germline cysts, the bridges interconnecting the proliferating germ cells are reinforced by microfilaments and microtubules occupy the open spaces of the bridges (Bilinsky and Jaglarz, 1999). During the differentiation of cystocytes into oocyte and germ cells, the oocyte consistently occupies a basal position in relation to the nurse cells (Patrício and Cruz-Landim, 2006).…”