To define the structural requirements of the parathyroid hormone (PTH)/PTH-related protein (PTHrP) receptor necessary for activation of phospholipase C (PLC), receptors with random mutations in their second cytoplasmic loop were synthesized, and their properties were assessed. A mutant in which the wild type (WT) rat PTH/PTHrP receptor sequence EKKY (amino acids 317-320) was replaced with DSEL had little or no PTH-stimulated PLC activity when expressed transiently in COS-7 cells, but it retained full capacity to bind ligand and to generate cAMP. This phenotype was confirmed in LLC-PK1 cells stably expressing the DSEL mutant receptor, where both PTH-stimulated PLC activity and sodium-dependent phosphate co-transport were essentially abolished. Individual mutations of these four residues point to a critical role for Lys-319 in receptor-G protein coupling. PTH-generated IPs were reduced to 27 ؎ 13% when K319E, compared with the WT receptor, and PLC activation was fully recovered in a receptor revertant in which Glu-319 in the DSEL mutant cassette was restored to the WT residue, Lys. Moreover, the WT receptor and a mutant receptor in which K319R had indistinguishable properties, thus suggesting that a basic amino acid at this position may be important for PLC activation. All of these receptors had unimpaired capacity to bind ligand and to generate cAMP. To ensure adequacy of G␣ q -subunits for transducing the receptor signal, G␣ q was expressed in HEK293 and in LLC-PK1 cells together with either WT receptors or receptors with the DSEL mutant cassette. PTH generated no inositol phosphates (IPs) in either HEK293 or LLC-PK1 cells, when they expressed DSEL mutant receptors together with G␣ q . In contrast, PTH generated 2-and 2.5-fold increases in IPs, respectively, when these cells co-expressed both the WT receptor and G␣ q . Thus, generation of IPs by the activated PTH/PTHrP receptor can be selectively abolished without affecting its capacity to generate cAMP, and Lys-319 in the second intracellular loop is critical for activating the PLC pathway. Moreover, ␣-subunits of the G q family, rather than ␤␥-subunits, transduce the signal from the activated receptor to PLC, and the PLC, rather than the adenylyl cyclase, pathway mediates sodium-dependent phosphate cotransport in LLC-PK1 cells.Signals from the parathyroid hormone (PTH) 1 /PTH-related peptide (PTHrP) receptor are transduced by G proteins. The lack of sequence homology between PTH/PTHrP receptors and all but a few of the other G protein-coupled receptors, however, justifies classifying them as members of a distinct family (1), which includes two mammalian receptors each for PTH or PTHrP (2, 3), vasoactive intestinal peptides (4, 5), and corticotrophin-releasing hormone (6), and receptors for secretin (7), calcitonin (8), glucagon-like peptide 1 (9), growth hormonereleasing hormone (10), glucagon (11), pituitary adenylyl cyclase-activating peptide (12), gastric inhibitory peptide (13), and an orphan receptor in brain similar to the calcitonin receptor (14). Recep...

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Around the onset of labor, uterine sensitivity to oxytocin (OT) increases tremendously. Although this is considered to reflect OT receptor (OTR) augmentation in myometrium, neither spatial expression of OTR nor the level of the receptor message during the course of pregnancy have been investigated at the molecular level. We examined the localization and expression of the OTR in human myometrium by means of in situ hybridization, immunohistochemistry, and Northern and Western blotting. In the term pregnant myometrium, OTR expressing smooth muscle cells are observed diffusely and heterogeneously. Some of the smooth muscle cells were expressed high levels of the receptor at the messenger RNA and protein level, and they were surrounded with cells weakly positive for the OTR or negative. The level of OTR transcripts increased according to the course of pregnancy. The receptor messenger RNA level reached over 300-fold at parturition compared with the nonpregnant myometrium. In the myometrium at 32 weeks of gestation and not in labor, a relatively large amount (about 100-fold) of the receptor message was expressed. In the nonpregnant myometrium, significant amount of the receptor protein was revealed by Western blotting. We also found that the receptor protein was augmented at term and after the onset of labor. These findings indicated that the expression of OTR changes dynamically at the transcription and protein level during pregnancy and that its expression is heterogeneous in the term myometrium.

Despite the importance of precisely regulating stem cell division, the molecular basis for this control is still elusive. Here, we show that surface glia in the developing Drosophila brain play essential roles in regulating the proliferation of neural stem cells, neuroblasts (NBs). We found that two classes of extracellular factors, Dally-like (Dlp), a heparan sulfate proteoglycan, and Glass bottom boat (Gbb), a BMP homologue, are required for proper NB proliferation. Interestingly, Dlp expressed in perineural glia (PG), the most outer layer of the surface glia, is responsible for NB proliferation. Consistent with this finding, functional ablation of PG using a dominant-negative form of dynamin showed that PG has an instructive role in regulating NB proliferation. Gbb acts not only as an autocrine proliferation factor in NBs but also as a paracrine survival signal in the PG. We propose that bidirectional communication between NBs and glia through TGF-β signaling influences mutual development of these two cell types. We also discuss the possibility that PG and NBs communicate via direct membrane contact or transcytotic transport of membrane components. Thus, our study shows that the surface glia acts not only as a simple structural insulator but also a dynamic regulator of brain development.

Intestinal stem cells (ISCs) are required for maintenance of the proper cell composition in the adult intestine. To ensure permanent recruitment of newly differentiated cells, the ISC undergoes asymmetric cell division that generates an ISC itself and a progenitor cell. In the Drosophila midgut, cell fate for the absorptive cell is determined by Notch (N) signal in the progenitor cells that receive a ligand Delta (Dl) produced by the ISCs. Although most of the ISCs and progenitor cells are distantly located, they should retain their attachment when N is activated because the Dl–N interaction requires cell adhesion. Furthermore, N cannot be activated before completion of cell division. Thus, the moment after cell division and before cell separation should be prolonged for certain N activation, although the mechanism for this remains unclear. Here, we demonstrate that E‐cadherin (E‐cad) is required for stable attachment between the two cells. When E‐cad does not function, N is not activated and cell differentiation is attenuated. We also show that the ISC tumor by N inactivation is assisted by a defect in E‐cad down‐regulation. These findings reveal one of the normal N functions used to inhibit tumorigenesis through lowering of E‐cad for proper midgut cell turnover.

Oxytocin (OT) is widely used to induce labor in the clinical setting. However, its physiological role in normal human parturition remains unclear. We demonstrated the enhanced expression of OT receptor (OTR) mRNA in chorio-decidual tissue, using the polymerase chain reaction after the reverse transcriptase reaction (RT-PCR)

SUMMARYIn Drosophila, ligands of the Unpaired (Upd) family activate the Janus kinase/signal transducers and activators of transcription (JAK/STAT) pathway. The JAK/STAT pathway controls many developmental events, including multiple functions in the ovary. These include an early role in the germarium for specification of stalk cells and a later role in the vitellarium to pattern the follicular epithelium surrounding each cyst. In this latter role, graded JAK/STAT activation specifies three distinct anterior follicular cell fates, suggesting that Upd is a morphogen in this system. Consistent with the JAK/STAT activation pattern in the vitellarium, Upd forms a concentration gradient on the apical surface of the follicular epithelium with a peak at its source, the polar cells. Like many morphogens, signaling and distribution of Upd are regulated by the heparan sulfate proteoglycans (HSPGs) Dally and Dally-like. Mutations in these glypican genes and in heparan sulfate biosynthetic genes result in disruption of JAK/STAT signaling, loss or abnormal formation of the stalk and significant reduction in the accumulation of extracellular Upd. Conversely, forced expression of Dally causes ectopic accumulation of Upd in follicular cells. Furthermore, biochemical studies reveal that Upd and Dally bind each other on the surface of the cell membrane. Our findings demonstrate that Drosophila glypicans regulate formation of the follicular gradient of the Upd morphogen, Upd. Furthermore, we establish the follicular epithelium as a new model for morphogen signaling in complex organ development.

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