Synchronized ATP oscillations have a critical role in prechondrogenic condensation during chondrogenesis

The skeletal elements of embryonic limb are prefigured by prechondrogenic condensation in which secreted molecules such as adhesion molecules and extracellular matrix have crucial roles. However, how the secreted molecules are controlled to organize the condensation remains unclear. In this study, we examined metabolic regulation of secretion in prechondrogenic condensation, using bioluminescent monitoring systems. We here report on ATP oscillations in the early step of chondrogenesis. The ATP oscillations depended on both glycolysis and mitochondrial respiration, and their synchronization among cells were achieved via gap junctions. In addition, the ATP oscillations were driven by Ca2+ oscillations and led to oscillatory secretion in chondrogenesis. Blockade of the ATP oscillations prevented cellular condensation. Furthermore, the degree of cellular condensation increased with the frequency of ATP oscillations. We conclude that ATP oscillations have a critical role in prechondrogenic condensation by inducing oscillatory secretion

The Golgin GMAP210/TRIP11 Anchors IFT20 to the Golgi Complex

Eukaryotic cells often use proteins localized to the ciliary membrane to monitor the extracellular environment. The mechanism by which proteins are sorted, specifically to this subdomain of the plasma membrane, is almost completely unknown. Previously, we showed that the IFT20 subunit of the intraflagellar transport particle is localized to the Golgi complex, in addition to the cilium and centrosome, and hypothesized that the Golgi pool of IFT20 plays a role in sorting proteins to the ciliary membrane. Here, we show that IFT20 is anchored to the Golgi complex by the golgin protein GMAP210/Trip11. Mice lacking GMAP210 die at birth with a pleiotropic phenotype that includes growth restriction, ventricular septal defects of the heart, omphalocele, and lung hypoplasia. Cells lacking GMAP210 have normal Golgi structure, but IFT20 is no longer localized to this organelle. GMAP210 is not absolutely required for ciliary assembly, but cilia on GMAP210 mutant cells are shorter than normal and have reduced amounts of the membrane protein polycystin-2 localized to them. This work suggests that GMAP210 and IFT20 function together at the Golgi in the sorting or transport of proteins destined for the ciliary membrane

Calcium ion currents mediating oocyte maturation events

During maturation, the last phase of oogenesis, the oocyte undergoes several changes which prepare it to be ovulated and fertilized. Immature oocytes are arrested in the first meiotic process prophase, that is morphologically identified by a germinal vesicle. The removal of the first meiotic block marks the initiation of maturation. Although a large number of molecules are involved in complex sequences of events, there is evidence that a calcium increase plays a pivotal role in meiosis re-initiation. It is well established that, during this process, calcium is released from the intracellular stores, whereas less is known on the role of external calcium entering the cell through the plasma membrane ion channels. This review is focused on the functional role of calcium currents during oocyte maturation in all the species, from invertebrates to mammals. The emerging role of specific L-type calcium channels will be discussed

Intercellular communication in spheroids

This chapter has shown that the response of spheroid cells to gap junctional communication may lead to certain metabolic and cell physiological changes. It has also become apparent that the functions of the gap junctions are very complex. They may, for example, be related to the fundamental effects of cAMP and/or Ca 2+. These lines of evidence should be pursued further. However, further insight into these functions may also be gained from a study of the structure and function of the gap-junctional proteins, as well as from a genetic approach (e.g., Willecke et al. 1982, 1983). In this context, the spheroids are of particular importance as test systems, since they perfectly simulate the three dimensional arrangement of cells encountered in a tissue. Indeed, the results presented in the sections "Biophysical and Biochemical Effects Associated with Intercellular Communications" and "Intercellular Communication and Radiosensitivity" have revealed clear cut differences between cells growing as spheroids or as monolayers in response to communication dependent processes, which indicate that the response of the monolayers could be somewhat trivial. The advantage of multicellular spheroid systems with three-dimensional growth over monolayer cultures is unquestionable. Cells growing in three-dimensional multicell spheroids may re-establish their regulatory activities and, therefore, match the in vivo conditions more closely. Multicell spheroids allow in vitro investigations on differentiating systems and on interactions between normal and malignant cells, thus substituting costly in vivo experiments

TMEM107 recruits ciliopathy proteins to subdomains of the ciliary transition zone and causes Joubert syndrome

The transition zone (TZ) ciliary subcompartment is thought to control cilium composition and signalling by facilitating a protein diffusion barrier at the ciliary base. TZ defects cause ciliopathies such as Meckel–Gruber syndrome (MKS), nephronophthisis (NPHP) and Joubert syndrome1 (JBTS). However, the molecular composition and mechanisms underpinning TZ organization and barrier regulation are poorly understood. To uncover candidate TZ genes, we employed bioinformatics (coexpression and co-evolution) and identified TMEM107 as a TZ protein mutated in oral–facial–digital syndrome and JBTS patients. Mechanistic studies in Caenorhabditis elegans showed that TMEM-107 controls ciliary composition and functions redundantly with NPHP-4 to regulate cilium integrity, TZ docking and assembly of membrane to microtubule Y-link connectors. Furthermore, nematode TMEM-107 occupies an intermediate layer of the TZ-localized MKS module by organizing recruitment of the ciliopathy proteins MKS-1, TMEM-231 (JBTS20) and JBTS-14 (TMEM237). Finally, MKS module membrane proteins are immobile and super-resolution microscopy in worms and mammalian cells reveals periodic localizations within the TZ. This work expands the MKS module of ciliopathy-causing TZ proteins associated with diffusion barrier formation and provides insight into TZ subdomain architecture

Gap junctional communication and development

Embryonic development requires extensive interaction between cells; cell-to-cell communication through gap junctions may be one mechanism involved. Much correlative evidence suggests gap junctions are involved in cellular interactions during development. Recently, the biological role of junctions has been investigated using antibodies prepared against the major rat liver gap junction protein. Disrupting normal patterns of intercellular communication with such antibodies can drastically perturb development. Recent experiments emphasize, in particular, the importance of gap junctional communication for patterning processes

Modulation of gap junction transcript and protein expression during pregnancy in the rat

Abstract. The expression of three different gap junction transcripts, or, (Cx43), B ~ (Cx39, and B2 (Cx26) was examined in several organs during pregnancy in the rat. In all of the organs that were examined-uterus, ovary, heart, and liver-there was a strong correlation between levels of gap junction mRNA and gap junction antigens that were detected at different stages of pregnancy. A striking change in o ~ transcript levels (a 5.5-fold increase) was detected in the uterine myometrium on the day before parturition. This elevation of the c~, transcript is thought to be associated with the formation of gap junctions that are required for synchronizing the contractility of the myometrial cells during parturition. 2 d before parturition, there was a detectable elevation of/32 transcripts and protein in th