Formation of gap and tight junctions between reaggregated blastomeres of the killifish, Fundulus

Abstract

Blastomeres from eggs of the killifish, Fundulus, were mechanically dissociated and reaggregated by pelleting in a simple saline solution. Formation of gap and tight junctions was followed by electron microscopy of freeze-fracture replicas. Five to eight min after pelleting, neither new nor old junctions were observed. After 10-15 min, small gap junctions were found, but these were not associated with distinct formation plaques. Larger gap junctions were observed after 45 min, and the images were consistent with growth by accretion of intramembrane particles. In aggregates, after 20 min or more, tight junctions were much more commonly found than in intact blastulae, and it seemed likely that they were being formed by cells that were not doing so in the intact embryo. Initial stages consisted of short strands that appeared to grow in length. Also, more elaborate junctions were seen than occur in situ. Particle-free membrane often occurred near incomplete junctions, and large junctions like those in situ separated particle-rich from particle-free membrane. In this system, the formation of both gap and tight junctions occurs with shorter latency, and is more precisely timed, than heretofore described.

Regulation of connexin43 expression and function by prostaglandin E 2 (PGE 2 ) and parathyroid hormone (PTH) in osteoblastic cells

“…Our results confirm and extend these observations, demonstrating that PGE 2 increases gap junctional communication between osteoblastic cells, but without changes in total Cx43 protein levels in whole cell extracts. Earlier work demonstrated that gap junctions may in fact be induced to aggregate without active protein synthesis [Ne'eman et al, 1980;Epstein et al, 1977], a phenomenon that has been recently described in more detail in mammary tumor cells stimulated by cAMP analogs [Atkinson et al, 1995]. This effect of cAMP occurred as early as 30 min of pharmacologic treatment, a time-course comparable to our findings.…”

Origin, form and function of extraembryonic structures in teleost fishes

“…The osmotic seal provided by the EVL helps to establish intra-embryonic conditions distinct from the surrounding environment [274,278] and is therefore essential for normal development. This protective function depends on the close lateral apposition of epithelial cells mediated by circumapical tight junctions, adherens junctions, desmosomes and gap junctions [59,177,178,182,[282][283][284][285][286], with the former playing the most critical permeability barrier role [182,282,283,286]. Indeed, studies in zebrafish demonstrate that disruption of tight junctions affects the barrier function of the EVL, as revealed by increased surface permeability of low molecular weight tracers, and compromised osmoregulation leading to increased sensitivity to osmotic stress and embryo rupture [286].…”

Η Διακυτταρική Επικοινωνία Στη Φυσιολογία Των Οστικών Κυττάρων

“…Παρόµοιος µηχανισµός δύο φάσεων φαίνεται να υπάρχει και για τη παραθορµόνη. Παλαιότερες µελέτες έχουν δείξει ότι είναι πράγµατι δυνατός ο σχηµατισµός νέων χασµοσυνδέσµων, χωρίς να προηγηθεί de novo σύνθεση κοννεξινών188,189 . Το φαινόµενο αυτό δεν περιορίζεται αποκλειστικά στα κύτταρα UMR106-01128,190 , αλλά είναι ιδιότητα και άλλων οστεοβλαστικών κυττάρων128,190 .…”