The cell adhesion molecule nectin-1 is critical for normal enamel formation in mice.

Nectin-1 is a member of a sub-family of immunoglobulin-like adhesion molecules and a component of adherens junctions. In the current study, we have shown that mice lacking nectin-1 exhibit defective enamel formation in their incisor teeth. Although the incisors of nectin-1-null mice were hypomineralized, the protein composition of the enamel matrix was unaltered. While strong immunostaining for nectin-1 was observed at the interface between the maturation-stage ameloblasts and the underlying cells of the stratum intermedium (SI), its absence in nectin-1-null mice correlated with separation of the cell layers at this interface. Numerous, large desmosomes were present at this interface in wild-type mice; however, where adhesion persisted in the mutant mice, the desmosomes were smaller and less numerous. Nectins have been shown to regulate tight junction formation; however, this is the first report showing that they may also participate in the regulation of desmosome assembly. Importantly, our results show that integrity of the SI-ameloblast interface is essential for normal enamel mineralization.

Effects of age on morphology, protein synthesis and secretagogue-evoked secretory responses in the rat lacrimal gland.

This study investigated changes in the morphology and protein synthesis and protein and peroxidase secretion due to peptidergic and aminergic stimulation from rat lacrimal gland acinar cells of 3-5, 9, 12, 20 and 24 month old rats. There was a marked reduction in the presence of Golgi apparatus in the acinar cells of glands from the 24 month old rats coupled to dilatation and degeneration of rough endoplasmic reticulum, when compared to that in the acinar cells of glands from 3-5 and 12 month old rats. Following incorporation of tritiated leucine for 360 min (6 h), the amount of newly synthesised protein in acinar cells of the 12 month old rats was significantly (p < 0.01) higher than that in the acinar cells of 3-5 month old animals. However, at 20 months the amount of newly synthesised protein in these acinar cells was significantly (p < 0.01) reduced to less than that in acinar cells of both the 3-5 and 12 month old animals. Immunohistochemical and immunofluorescence studies identified the presence of substance P (SP), vasoactive intestinal peptide (VIP), histamine and 5-hydroxytryptamine (5-HT) in the lacrimal glands of 3-5 month old rats. Stimulation by either SP, VIP, histamine or 5-HT resulted in significant increases in total protein output and peroxidase release from acinar cells of the 3-5 month old rats. However, all responses to the secretagogues were reduced with ageing from 3-5 to 24 months of age. The results indicate that ageing is associated with alteration in the ability of acinar cells to synthesise and secrete proteins.

Defective cell cycle control underlies abnormal cortical development in the hydrocephalic Texas rat.

There is a significant body of evidence to suggest a physiological role for the CSF in both the developing and adult brain. Our recent studies suggest a critical role for this fluid in the developing brain of the hydrocephalic Texas (H-Tx) rat. A key feature of the foetal-onset hydrocephalus in this rat is obstruction in the flow and/or absorption of fluid that is associated with abnormal development of the cerebral cortex resulting in a reduction in the number of neuronal precursors generated. Cells from the affected cerebral cortex do proliferate in vitro and show dose-dependent responses to growth factor stimulation, suggesting that germinal cells are under inhibitory influences in vivo. We tested the hypothesis that the CSF of the affected brains was responsible for the abnormal development. Cells analysed at the time of extraction from affected brains showed an accumulation of cells in the S-phase of the cell cycle, which was reflected in a concentration of cells containing high levels of DNA in the germinal matrix of histological sections of affected brains. CSF from the lateral ventricle of affected foetal brains not only inhibited in vitro proliferation of normal neuronal progenitors, but it also resulted in an accumulation of cells in the S-phase of the cell cycle mimicking the situation in vivo. Fluid from normal foetal brains did not have this effect. From the work detailed here on the mechanistic basis of the deficient cortical development in the foetal hydrocephalic rat brain, we conclude that the content of the CSF is critical in maintaining germinal matrix function and output and, therefore, that the CSF has a vital role in brain development.

Deficient cortical development in the hydrocephalic Texas (H-Tx) rat: a role for CSF.

The objectives of this study were to demonstrate the presence and nature of abnormal cortical development in a rat model of hydrocephalus, the hydrocephalic Texas (H-Tx) rat, and to test the hypothesis that the obstruction of CSF flow in affected animals can be linked to this effect. CSF is secreted continuously by the choroid plexus, located in the lateral, third and fourth ventricles. The fluid flows through the ventricular system, passing over all regions of germinal activity. In the H-Tx rat, obstruction and eventual blockage of CSF flow occurs in the cerebral aqueduct, between the third and fourth ventricles, at embryonic day 18. Prior to obstruction, neurogenesis and migration occur as in normal rats. Here we show that, following obstruction of fluid flow, neurogenesis from the germinal epithelium becomes abnormal. Cell proliferation decreases and proliferating cells are not retained in the germinal layer, as they appear to be in the normal brain. Cell migration is apparently unaffected, although a decrease in the number of migrating cells does occur after CSF obstruction. These data from our study indicate that a rapid primary effect of CSF obstruction, prior to any mechanical effects of fluid accumulation, is to alter the activity of cells in the germinal epithelium of the developing cortex. Further evidence for this is gained from in vitro studies. Once removed from their in vivo environment, cortical cells from the H-Tx rat have the ability to proliferate as normal. CSF extracted from the enlarged ventricles of affected brains is able to inhibit the proliferation of normal cells. Thus, we hypothesize that CSF has a potential role in the developmental process. The damming up and accumulation of CSF, whatever the cause, may result in abnormal cortical development through accumulation of CSF factors that are, or become, inhibitory to normal neuronal proliferation.