Mucinoprotein is a universal constituent of stable intercellular bridges inDrosophila melanogaster germ line and somatic cells

Abstract

Intercellular bridges formed by incomplete cytokinesis may be important in a variety of processes, including synchronization of mitotic and meiotic divisions in animal cells. Using specific antibodies against a mucin‐type glycoprotein (Kramerov et al. 1996 FEBS Lett. 378:213–218) from Drosophila melanogaster cultured embryonic cells, we showed that this glycoprotein is located in all cytoplasmic bridges found in various germline and somatic tissues. In the ovary, immunostaining of ring canals connecting germ cells can be detected in the very early stages at the germarium region 1 where first gonial divisions take place, and the immunostaining appears to persist through late stages when transport of cytoplasm from nurse cells to a growing oocyte occurs. Each ring canal is made up of an outer and an inner rim. Mucin glycoprotein appears to be one of the first proteins localized to the outer rim, which is a derivative of the arrested cleavage furrow. The known ring canal proteins, phosphotyrosine‐containing protein(s), F‐actin, hts‐ and kelch proteins, are localized to the inner rim at a later developmental time. Similarly, mucin glycoprotein is recruited early to ring canals connecting mitotic primary spermatocytes in both larval and adult testes. Mucin glycoprotein was found to be present in intercellular bridges (small ring canals) in somatic cells, including follicular epithelium in ovary and imaginal disc cells. Intercellular bridges were observed for the first time in a subset of cells in the larval brain. Thus, mucin glycoprotein is the only protein hitherto found in all known types of stable intercellular bridges and may be an important constituent of a backbone needed for assembly and preservation of this particular type of cell‐cell contact. Dev Dyn 1999;216:349–360. ©1999 Wiley‐Liss, Inc.

Analysis of the gene expression profile of mouse male meiotic germ cells

“…2). Interestingly, another component of the mucosal glycocalyx, contributing to anti-adhesive and protective cell functions, mucin1, has been reported to be expressed in maturing germ cells of the human testis (Franke et al, 2001), and a mucin glycoprotein was found to be an universal constituent of stable intercellular bridges in the Drosophila melanogaster germ line (Kramerova and Kramerov, 1999). Few receptors for potential growth factors were found to be expressed in spermatocytes through the microarray analysis.…”

Intercellular protein movement in syncytialDrosophilafollicle cells

“…Vsg is a predicted sialomucin protein with a single transmembrane domain and multiple predicted extracellular O-linked glycosylation sites. Its localization to somatic ring canals is highly reminiscent of Mucin-D localization (Kramerova and Kramerov, 1999); however, we were unable to confirm this directly because Mucin-D antibodies are no longer available. Vsg (and Mucin-D) are also present in ring canals of larval imaginal disc and brains.…”

“…Several other proteins have been reported in follicle cell or imaginal disc ring canals based on confocal microscopy: Pavarotti kinesin-like protein (Pav-KLP) (Minestrini et al, 2002), Anillin (de Cuevas and Spradling, 1998), Mucin-D (Kramerova and Kramerov, 1999), Visgun (Vsg) Nystul and Spradling, 2007), Nasrat and Polehole (Jimenez et al, 2002). Recent work confirmed the presence of Pav-KLP and Anillin in Drosophila somatic ring canals, as well as another protein called Cindr, using a combination of immunoEM and confocal microscopy (Haglund et al, 2010).…”

Bridging the divide

“…[8][9][10] Somatic RCs in all these tissues were consistently found to have an electron dense backbone 50 nm thick with an average lumenal diameter of approximately 250 nm. The variety of tissues containing RCs make Drosophila an interesting and technically accessible system for studying the formation and function of RCs.…”