Cyclic AMP-dependent activation of rhodopsin gene transcription in cultured retinal precursor cells of chicken embryo

Cyclic AMP-dependent regulation of tyrosine hydroxylase mRNA and immunofluorescence levels in rat retinal precursor cells

Stimulation of tyrosine hydroxylase (TH) gene transcription by cyclic AMP (cAMP) has been clearly established in adrenal medula cells and neural-crest-derived cell lines but information on this mechanism is still lacking in dopaminergic neurons. Because they are easily amenable to in vitro experiments, dopaminergic amacrine cells of the retina might constitute a valuable model system to study this mechanism. We have used real-time reverse transcription with the polymerase chain reaction to quantify TH mRNA levels in the rat retina during post-natal development and in retinal precursor cells obtained from neonatal rats and cultured for 3 days in serum-free medium. Whereas the TH mRNA concentration remains consistantly low in control cultures, treatment with cAMP-increasing agents (forskolin, membrane depolarization, phosphodiesterase inhibitors) is sufficient to raise it to the level observed in adult retina (15-fold increase). Treatment of the cultured cells can be delayed by up to 2 days with identical results at the TH mRNA level, thus ruling out a survival-promoting effect of cAMP. TH immunofluorescence has confirmed cAMP-dependent regulation of TH expression at the protein level and indicates that the frequency of TH-positive cells in the cultures is similar to that observed in the adult retina. Selective phosphodiesterase inhibitors suggest that PDE4 is the major subtype involved in the dopaminergic amacrine cell response. Our data clearly establish the cAMP-dependent regulation of TH mRNA and immunofluorescence levels in retinal precursor cells. The possible role of this regulation mechanism in the developmental activation of TH gene expression is discussed.

Visual photoreceptor subtypes in the chicken retina: melatonin-synthesizing activity and in vitro differentiation

The chicken retina contains five visual photoreceptor subtypes, based on the specific opsin gene they express. In addition to the central role they play in vision, some or all of these photoreceptors translate photoperiodic information into a day-night rhythm of melatonin production. This indolic hormone plays an important role in the photoperiodic regulation of retinal physiology. Previous studies have stopped short of establishing whether melatonin synthesis takes place in all the photoreceptor spectral subtypes. Another issue that has been left unsettled by previous studies is when during development are retinal precursor cells committed to a specific photoreceptor subtype and to a melatoninergic phenotype? To address the first question, in situ hybridization of the five opsins was combined with immunofluorescent detection of the melatonin-synthesizing enzyme hydroxyindole O-methyltransferase (HIOMT, EC.2.1.1.4). Confocal microscopy clearly indicated that all photoreceptor spectral subtypes are involved in melatonin synthesis. To tackle the second question, retinal precursor cells were dissociated between embryonic day 6 (E6) and E13 and cultured in serum-free medium for 4 days to examine their ability to autonomously activate the expression of opsins and HIOMT. Real-time PCR on cultured precursors indicated that red-, green- and violet-sensitive cones are committed at E6, rods at E10 and blue-sensitive cones at E12. HIOMT gene expression was programmed at E6, probably reflecting the differentiation of early cones. The present study provides a better characterization of photoreceptor subtypes in the chicken retina and describes a combination of serum-free culture and real-time PCR that should facilitate further developmental studies.

Interaction of profilin-1 and F-actin via a β-arrestin-1/JNK signaling pathway involved in prostaglandin E(2)-induced human mesenchymal stem cells migration and proliferation

Although many previous reports have examined the function of prostaglandin E(2) (PGE(2)) in the migration and proliferation of various cell types, the role of the actin cytoskeleton in human mesenchymal stem cells (hMSCs) migration and proliferation has not been reported. The present study examined the involvement of profilin-1 (Pfn-1) and filamentous-actin (F-actin) in PGE(2)-induced hMSC migration and proliferation and its related signal pathways. PGE(2) (10(-6) M) increased both cell migration and proliferation, and also increased E-type prostaglandin receptor 2 (EP2) mRNA expression, β-arrestin-1 phosphorylation, and c-Jun N-terminal kinase (JNK) phosphorylation. Small interfering RNA (siRNA)-mediated knockdown of β-arrestin-1 and JNK (-1, -2, -3) inhibited PGE(2)-induced growth of hMSCs. PGE(2) also activated Pfn-1, which was blocked by JNK siRNA, and induced F-actin level and organization. Downregulation of Pfn-1 by siRNA decreased the level and organization of F-actin. In addition, specific siRNA for TRIO and F-actin-binding protein (TRIOBP) reduced the PGE(2)-induced increase in hMSC migration and proliferation. Together, these experimental data demonstrate that PGE(2) partially stimulates hMSCs migration and proliferation by interaction of Pfn-1 and F-actin via EP2 receptor-dependent β-arrestin-1/JNK signaling pathways.