Cyclic-nucleotide phosphodiesterase: an early defect in inherited retinal degeneration of C3H mice

Photoperiodic effects on monoamine signaling and gene expression throughout development in the serotonin and dopamine systems

Photoperiod or the duration of daylight has been implicated as a risk factor in the development of mood disorders. The dopamine and serotonin systems are impacted by photoperiod and are consistently associated with affective disorders. Hence, we evaluated, at multiple stages of postnatal development, the expression of key dopaminergic (TH) and serotonergic (Tph2, SERT, and Pet-1) genes, and midbrain monoamine content in mice raised under control Equinox (LD 12:12), Short winter-like (LD 8:16), or Long summer-like (LD 16:8) photoperiods. Focusing in early adulthood, we evaluated the midbrain levels of these serotonergic genes, and also assayed these gene levels in the dorsal raphe nucleus (DRN) with RNAScope. Mice that developed under Short photoperiods demonstrated elevated midbrain TH expression levels, specifically during perinatal development compared to mice raised under Long photoperiods, and significantly decreased serotonin and dopamine content throughout the course of development. In adulthood, Long photoperiod mice demonstrated decreased midbrain Tph2 and SERT expression levels and reduced Tph2 levels in the DRN compared Short photoperiod mice. Thus, evaluating gene × environment interactions in the dopaminergic and serotonergic systems during multiple stages of development may lead to novel insights into the underlying mechanisms in the development of affective disorders.

The occurrence of tarsal injuries in male mice of C57BL/6N substrains in multiple international mouse facilities

Dislocation in hindlimb tarsals are being observed at a low, but persistent frequency in group-housed adult male mice from C57BL/6N substrains. Clinical signs included a sudden onset of mild to severe unilateral or bilateral tarsal abduction, swelling, abnormal hindlimb morphology and lameness. Contraction of digits and gait abnormalities were noted in multiple cases. Radiographical and histological examination revealed caudal dislocation of the calcaneus and partial dislocation of the calcaneoquartal (calcaneus-tarsal bone IV) joint. The detection, frequency, and cause of this pathology in five large mouse production and phenotyping centres (MRC Harwell, UK; The Jackson Laboratory, USA; The Centre for Phenogenomics, Canada; German Mouse Clinic, Germany; Baylor College of Medicine, USA) are discussed.

Sequential Photoperiodic Programing of Serotonin Neurons, Signaling and Behaviors During Prenatal and Postnatal Development

Early life stimuli during critical developmental time frames have been linked to increased risk for neurodevelopmental disorders later in life. The serotonergic system of the brain is implicated in mood disorders and is impacted by the duration of daylight, or photoperiod. Here we sought to investigate sensitive periods of prenatal and postnatal development for photoperiodic programming of DRN serotonin neurons, midbrain serotonin and metabolite levels along with affective behaviors in adolescence (P30) or adulthood (P50). To address these questions we restricted the interval of exposure to prenatal development (E0-P0) for Long summer-like photoperiods (LD 16:8), or Short winter-like photoperiods (LD 8:16) with postnatal development and maturation then occurring under the opposing photoperiod. Prenatal exposure alone to Long photoperiods was sufficient to fully program increased excitability of DRN serotonin neurons into adolescence and adulthood, similar to maintained exposure to Long photoperiods throughout development. Interestingly, Long photoperiod exposure can elevate serotonin and its’ corresponding metabolite levels along with reducing affective behavior, which appear to have both pre and postnatal origins. Thus, exposure to Long photoperiods prenatally programs increased DRN serotonin neuronal excitability, but this step is insufficient to program serotonin signaling and affective behavior. Continuing influence of Long photoperiods during postnatal development then modulates serotonergic content and has protective effects for depressive-like behavior. Photoperiodic programing of serotonin function in mice appears to be a sequential process with programing of neuronal excitability as a first step occurring prenatally, while programing of circuit level serotonin signaling and behavior extends into the postnatal period.

Genetic complexity of absence seizures in substrains of C3H mice

Absence epilepsy is a common form of idiopathic generalized epilepsy whose etiology is poorly understood because of genetic and phenotypic heterogeneity. The inbred mouse strain C3H/He exhibits spontaneous absence seizures characterized by spike and wave discharges (SWD) on the electroencephalogram concomitant with behavioral arrest. Previous studies using the C3H/HeJ (HeJ) substrain identified a mutation in the Gria4 gene as a major susceptibility locus. In the present study, we found that two closely related substrains C3H/HeOuJ (OuJ) and C3H/HeSnJ, which have a similar SWD incidence as HeJ, do not contain the Gria4 mutation. Further analysis of backcross mice segregating OuJ and C57BL/6J alleles shows that, unlike the HeJ substrain, OuJ does not have a major locus for SWD but has suggestive loci at best that would explain only a fraction of the phenotypic variance. These results illustrate how the genetic etiology of a common neurological disorder can differ between substrains with similar phenotypes. We infer that all C3H strains are sensitized to SWD and that additional mutations affecting SWD arose or were fixed independently in the years since the substrains diverged.

Evolving neurovascular relationships in the RCS rat with age

PURPOSE

To examine the course of development of vascular disorders in the Royal College of Surgeons (RCS) rat and how these may lead to retinal ganglion cell loss.

METHODS

Whole-mount retinae from RCS rats were first stained for neurofilament protein and then for NADPH-diaphorase staining. A separate group of RCS rats was injected with Type II Peroxidase and the retinae were subsequently processed for peroxidase histochemistry.

RESULTS

The first changes in the deep vascular plexus occur as the photoreceptor layer is lost and it comes into close proximity to the retinal pigment epithelial (RPE) cell layer. RPE cells migrate onto retinal vessels, and at such locations vascular complex develop. These are first found ventral to the optic nerve head and then gradually progress over most of the retina. The inner retinal vessels that supply the complexes cross the optic nerve fiber layer and appear to be under tension. They ligate axons, which leads to retinal ganglion cell loss.

CONCLUSIONS

These observations show vascular changes can have secondary repercussions for neurons distant from the primary lesion.

PCR analysis of DNA from 70-year-old sections of rodless retina demonstrates identity with the mouse rd defect

Rodless retina (gene symbol, r) was discovered in mice by Keeler 70 years ago and was first described in this journal as an autosomal recessive mutation leading to "the absence of the visual cells (rods), the external nuclear layer, and the external molecular layer" [Keeler, C. E. (1924) Proc. Natl. Acad. Sci. USA 10, 329-333]. The mutation was studied by Keeler and others in the United States and Europe over the next decade, but Keeler's stock was destroyed in 1939, and mice definitively related to his by pedigree and progeny tests also appeared to have been lost by the end of World War II. In the early 1950s Brückner in Basel recognized mice with a similar retinal phenotype. Investigators in London and Strasbourg analyzed descendants of Brückner's mice and concluded, on the basis of different pathogenesis from r, that they carried a new mutation, which came later to be called retinal degeneration, rd. The relationship of r and rd has been unsettled ever since. Now that the rd phenotype is known to be due to a nonsense mutation in the rod photoreceptor cGMP phosphodiesterase beta-subunit gene, we hoped to settle the question by direct analysis of r DNA. DNA was liberated from 70-year-old histological sections of +/r and r/r eyes, the only extant r DNA, and the regions encompassing the nonsense mutation amplified by the polymerase chain reaction (PCR). Sequence analysis of the PCR products revealed the presence of the same nonsense mutation and two intron polymorphisms in r DNA. PCR and direct sequence analysis of 11 strains of mice known to carry rd (or a similar allele) also revealed the presence of the nonsense mutation and the same intron polymorphisms. The fact that all r and rd mice contain an identical defect and intron polymorphisms in the phosphodiesterase beta-subunit gene settles beyond reasonable doubt that a single mutation arising > 70 years ago is now widely distributed through inbred mouse strains. Because of the extensive use of the name in publications of the past 40 years, we propose that the gene continue to be designated retinal degeneration, rd.

Apoptosis: final common pathway of photoreceptor death in rd, rds, and rhodopsin mutant mice

Mutations in the retinal degeneration, retinal degeneration slow(/peripherin) and rhodopsin genes cause photoreceptor degeneration in humans and mice. Although the phenotypes arising from these mutations are different, suggesting different mechanisms of pathogenesis, we present evidence that apoptosis may be the final common pathway of the disease process linking genotype to phenotype. We observed internucleosomal cleavage of retinal DNA by gel electrophoresis and fragmented DNA at the single cell level by labeling the nicked DNA ends with biotinylated poly(dU). In retinal degeneration mice, DNA fragmentation occurred during the period of photoreceptor degeneration. In retinal degeneration slow mice and in transgenic mice expressing a mutant (Pro347Ser) rhodopsin gene, DNA fragmentation occurred after normal histogenetic cell death (also apoptosis) had ceased. Since DNA fragmentation by internucleosomal cleavage is a cardinal feature of apoptosis, our data suggest that all three of these genetic mutations lead to apoptosis.

Developmental expression of a synaptic ribbon antigen (B16) in mouse retina

We investigated the developmental expression of the synaptic antigen B16 in the outer and inner plexiform layers in the retina. We compared the expression of this protein with published accounts of retinal ribbon synaptogenesis. The time course of B16 expression was found to be similar, if not identical, to the time course of synaptogenesis in the photoreceptor terminal, supporting our idea of the synaptic nature of the B16 protein. This study provides further evidence which suggests that the B16 antigen is a ribbon associated protein. The morphology, location, and developmental expression of this antigen is coincident with the structure and development of the ribbon synaptic elements located in both the photoreceptor and bipolar terminals. The emergence of the B16 protein was also examined in retina from mice homozygous for the retinal degeneration (rd) mutation which affects photoreceptor synaptogenesis. The B16 expression in the rd retina parallels that in the wild-type retina at early stages of development. However, significant changes in the morphology and staining pattern of the B16 antigen in the rd retina occurring at later postnatal stages are consistent with the degeneration observed in the photoreceptor terminals.

High-affinity cAMP phosphodiesterase and adenosine localized in sensory organs

Odorant-stimulated formation of cAMP in olfactory receptor neurons may mediate olfactory signal transduction. The response is short and desensitization occurs rapidly, possibly by induction of cyclic nucleotide phosphodiesterase (PDE) activity. Previously, we showed that two low Km PDEs regulate hydrolysis of cAMP in olfactory cilia. One PDE is Ca2+/calmodulin-dependent and non-selective for both cAMP-PDE and cGMP; the other is Ca2+/calmodulin-independent, sensitive to rolipram and selective for cAMP. We have localized cAMP-selective PDE in olfactory, gustatory and retinal sensory systems by autoradiography with the selective inhibitor [3H]rolipram. We observe dense binding over olfactory neurons, particularly over olfactory nerve bundles and olfactory cilia. In the tongue apical regions of taste buds of the circumvallate papillae are strongly labeled as well as portions of the glossopharyngeal nerve. Retinal binding is most dense over the inner plexiform layer, ganglion cells and the optic nerve but is also substantial over the inner nuclear layer. The pattern of [3H]rolipram-binding in retina is reminiscent of adenosine localization. Accordingly, adenosine was immunohistochemically localized in olfactory, gustatory and retinal tissues. Adenosine immunoreactivity is observed in olfactory neurons, in the basal regions of taste buds and in retinal ganglion cells.

Retinitis pigmentosa

Retinitis pigmentosa is a clinically and genetically heterogeneous group of hereditary disorders in which there is progressive loss of photoreceptor and pigment epithelial function. The prevalence of retinitis pigmentosa is between 1/3000 and 1/5000 making it one of the most common causes of visual impairment in all age groups. The natural history, differential diagnosis, diagnostic clinical and electrophysiologic findings are reviewed. Generalization about the different genetic subtypes of retinitis pigmentosa are reviewed along with the uses of DNA probes for linkage studies. Syndromes in which retinitis pigmentosa is a manifestation are summarized.

Retinal dystrophy: development retarded by galactose feeding in spontaneously hypertensive rats

Retinal photoreceptor cell dystrophies have been widely observed in humans and in animals, but pathogenetic mechanisms are known in only a few such disorders, and successful therapeutic intervention has been reported in fewer still. Spontaneously hypertensive albino rats develop a retinal photoreceptor cell dystrophy with onset late in the first year or early in the second year of life. Between 60 and 70 percent of the animals are affected. A substantial reduction in the prevalence and severity of the dystrophy occurred in such animals whose diet contained 30 percent (by weight) D-galactose. Neither an inhibitor of the enzyme aldose reductase, present in the diet, nor diabetes mellitus, induced by streptozotocin, had any statistically significant influence on the dystrophy. Ambient light and systolic blood pressure levels also did not seem to influence the course of the disorder. The mechanism by which galactose exerts its effect is unknown, but a mutant enzyme with an elevated Michaelis constant (Km) for galactose is plausible.

Soluble retinal proteins associated with photoreceptor cell death in the rd mouse

In the mouse, the homozygous presence of the rd gene results in the genetically programmed death of the photoreceptor cells of the retina. Using congenic strains of mice and a novel, sensitive, immunological approach for visualizing unique retinal proteins, we identified four bands of protein whose concentrations are regulated by the homozygous presence of the gene for retinal degeneration. Since these proteins (with apparent molecular weights of 23, 33, 55, and 69 kD) are present in normal adult mouse retinas and absent from rodless retinas, and from other mouse non-retinal tissues including brain, heart, kidney and liver, the data support the identification of these proteins as being retina specific. These proteins are not peculiar to the normal mouse retina; but rather, all four (23, 33, 55 and 69 kD) are common to rat retina; three (23, 33, and 55 kD) are common to bovine retina; and presently at least two, 23 and 69 kD, are clearly detectable in normal, adult human retina. The temporal appearance and disappearance of the four retinal specific protein bands coincide with the morphological maturation and degeneration of the photoreceptor cell population. Collectively, the present data suggest that one or more may be photoreceptor specific. These observations present the first step in the identification and characterization of specific soluble proteins correlated with the biochemical phenotype of the rd gene and the death of photoreceptor cells of the retina.

Enhancement of (polyA+)RNA synthesis in light in isolated intact photoreceptor cells of the rat

Incorporation of [3H]-cytidine into messenger RNAs (polyadenylated RNAs) was enhanced in light in isolated intact photoreceptor cells of the rat. The increase in polyadenylated (PolyA+)RNAs appeared selective relative to other photoreceptor RNAs since incorporation of [3H]-cytidine into this fraction was up to 10-fold higher while labeling of total cellular RNAs was only two- to three-fold higher in light compared with dark. The photoreceptor cells were isolated in vivo through destruction of inner retina neurons with injections of combinations of neurotoxic substances during early postnatal development. The photoreceptor cells attained normal adult morphology and function: the alpha-wave of the electroretinogram, as well as the thickness of the outer nuclear layer and the length of photoreceptor inner and outer segments, were found to be within the normal range at 4 and 10 weeks of age. In addition to RNA synthesis, such photoreceptor cell preparations when incubated in vitro demonstrated a capacity for regulating light-dependent sodium fluxes comparable to that within the intact retina. The potential usefulness of this model for exploring the molecular biology of photoreceptor cells is discussed.

Studies on hereditary retinal degeneration. The rd gene in the mouse

Stearic, oleic, linoleic, arachidonic, and docosahexaenoic acids can be detected regularly in the eyes and retinae of mice. During the period of maturation of the outer segments of the rod, the amount of each fatty acid increases, the most striking feature of which is the accumulation of docosahexaenoic acid in the retina, which might reflect the growth of rod outer segments. In rd/rd mice, fatty acid synthesis is reduced and the change characteristic of docosahexaenoic acid is absent. Analysis of the structure of outer segment disc membranes by the freeze fracturing technique, however, shows that the structure of the membrane is probably not affected by the rd gene.

Cyclic nucleotide content and phosphodiesterase activity in the rds mouse (020/A) retina

Cyclic nucleotide metabolism was examined in the retina and in the retinal pigment epithelium (RPE)-choroid complex of the rds mouse (020/A), a mutant in which discrete photoreceptor outer segment disc structures fail to develop. In retinas of both rds and control (Balb/c) mice, cyclic AMP levels peak at 10-15 days (20-25 pmol mg-1 protein). The level drops to about 10 pmol mg-1 at about one month in normal retinas but remains high in affected retinas. Cyclic GMP levels increase five-fold in Balb/c retinas as ROS develop whereas, in affected retinas, the levels remain constant and low (about 5 pmol mg-1). In RPE-choroid, cyclic nucleotide levels are similar in control and affected mice. Cyclic AMP phosphodiesterase (PDE) activity is somewhat higher in affected than in control retinas; conversely, cyclic GMP-PDE is lower. Both cyclic AMP-PDE and cyclic GMP-PDE activities are different in normal and affected RPE-choroid. Thus, although the rds (020/A) mouse belongs to the early-onset photoreceptor dysplasia group of hereditary retinal degenerations on a morphological basis, it does not exhibit high retinal cyclic GMP levels and thus appears to be distinct from other animals exhibiting early postnatal photoreceptor dysfunction.

Cytidine metabolism in photoreceptor cells of the rat

During brief (30-min) incubations, isolated rat retinas accumulated [3H]cytidine, converted it to cytidine triphosphate (CTP), and incorporated it into RNA and cytidine diphosphate-diacylglyceride (CDG), a phospholipid precursor of phosphatidylinositol (Pl). Labeled CTP, RNA, and CDG contents were found to be two- to three-fold higher in photoreceptor cells than in cells of the inner retina. Autoradiograms showed that, within photoreceptor cells, silver grains representing RNA were concentrated over the nuclei in dark and light, while silver grains representing CDG were concentrated over the inner segments only after incubation in dark. The formation of labeled CTP and the synthesis of RNA were enhanced in light, while labeled CDG levels became reduced in light concurrent with an increase in the incorporation of labeled inositol into Pl. The 3H-labeled CDG content, however, was increased two- to fourfold in light in the presence of actinomycin D, and autoradiograms show a heavy concentration of silver grains over the inner segments of photoreceptor cells. These findings establish a role for cytidine nucleotides in photoreceptor cell metabolism and in light-dependent increases in RNA and Pl synthesis. Furthermore, the observations indicate that a competition may exist in light for cytidine or CTP and suggest that availability of cytidine for CDG synthesis may have a regulatory role in Pl metabolism within the photoreceptor cells.

Light enhances the turnover of phosphatidylinositol in rat retinas

Light stimulation of isolated rat retinas is shown to enhance the turnover of phosphatidylinositol (PI) as demonstrated by a light-dependent increase in [3H]inositol incorporation and concurrent hydrolysis of existing PI. Studies with rat retinas incubated with [3H]inositol and then microdissected at the level of the outer plexiform layer into photoreceptor cell and inner retina layers indicated that the light-enhanced incorporation of [3H]inositol was associated with the photoreceptor cell layer. The rate of PI hydrolysis in retinas prelabeled in vivo with [3H]inositol was higher in light than in dark incubations and was higher in the photoreceptor cell layer than within the inner retina. Within the photoreceptor cell layer. PI turnover involved 2%/min of the total PI content in dark and 6-8%/min in light. In contrast to what has been reported for stimulus-enhanced turnover of PI in some tissues, this light-enhanced turnover of PI in the retina was not associated with detectable reductions in PI content. Parallel studies of sodium (22Na) uptake demonstrated that the photoreceptor cells remained functional during these incubations as they retained the capacity to restrict the entry of 22Na in light but not in dark.

Retinal degeneration in the pcd cerebellar mutant mouse. II. Electron microscopic analysis

The cerebellar ataxia in Purkinje cell degeneration (pcd) mutant mice results from the rapid loss of Purkinje cells between 3 and 5 weeks after birth. The loss of photoreceptors in these mutants begins about the same time but proceeds slowly, with most photoreceptors being lost by 1 year of age. In this study the retinas of pcd/pcd mice and their littermate controls from the age of 10 postnatal days to 15 months were analyzed by electron microscopy. The first signs of photoreceptor cell degeneration are apparent in the region of photoreceptor inner segments as early as postnatal day 13, and more prominently at day 18. During this time, the degeneration is characterized by a large number of vesicles, ranging in diameter from 150 to 350 nm, which are located in the extracellular space adjacent to the photoreceptor inner segments. Analysis of serial sections shows that most of these membrane-bound degeneration profiles are tubular in shape and some are continuous with the cell membrane of the inner segment. Therefore, these "profiles" are thought to arise from tubular outpocketings of the inner segments which cleave off to form isolated membrane-bound profiles. This represents a new and unusual form of photoreceptor degeneration. While the most obvious abnormality in the retina is degeneration of photoreceptor cells, Müller cells also appear to be affected, with swollen apical processes often seen coursing through the outer nuclear layer.

A heat-stable protein inhibitor of cyclic 3',5'-nucleotide phosphodiesterase

A heat-stable, non-dialyzable inhibitory factor of cyclic nucleotide phosphodieterase was detected in and partially purified from bovine retina. The factor appears to be a protein, since the inhibitory activity was abolished by trypsin digestion but not by DNAase or RNAase treatment. The protein inhibitor from bovine retina effectively inhibits the Ca2+-independent phosphodiesterase from several sources, including bovine retina, bovine rod outer segment, and a human lymphoblastic leukemia cell line, indicating lack of tissue and species specificity.

Protein activator of cyclic AMP phosphodiesterase and cyclic nucleotide phosphodiesterase in bovine retina and bovine lens. Activity, subcellular distribution and kinetic parameters

We have examined the activity of cyclic AMP phosphodiesterase, cyclic GMP phosphodiesterase and the protein activator of cyclic AMP phosphodiesterase in various anatomic and subcellular fractions of the bovine eye. Cyclic GMP hydrolysis was 1.6--12 times faster than hydrolysis of cyclic AMP in the subcellular fractions of the retina and in the precipitate of the rod outer segment. An opposite pattern was seen in the bovine lens, where the hyrolysis of cyclic AMP occurred 17 and 169 times faster than that of cyclic GMP in the supernatant and precipitate of lens, respectively. The activity of cyclic AMP phosphodiesterase was not affected by ethylene-glycol bis(beta-aminoethylether)-N,N'-tetraacetic acid in any fractions except in the retinal supernatant, suggesting that the phosphodiesterase exists primarily as a Ca2+-independent, activator-independent form. However, the protein activator of cyclic AMP phosphodiesterase existed in all fractions examine. A complex kinetic patternwas observed for both cyclic AMP and cyllic GMP hydrolysis by the 105000 times g lens supernatant. The Michaelis constants for both cyclic AMP (1.3-10(-6) and 9.I-10(-6) M) and cyclic GMP (1.04-10(6) AND 1.22 10(-5) M) appeared to be similar.

Studies of visual function and its decay in mice with hereditary retinal degeneration

Functional implications of mouse hereditary retinal degeneration have been studied at the level of the superior colliculus and visual cortex in the C57BL/6J-le rd strain. On autoradiography at a light-microscopic level, following eye injection with radioactive compounds, central visual structures appeared normal. A slight reduction in ipsilateral retinal projection was probably related to reduced retinal pigmentation associated with the light ear (le) mutation. In recordings from visual cortex and tectum in rd mice older than five months the cells discharged with highly rhythmic maintained activity. This ongoing activity depended on retinal input, since temporary asphyxia of the eye stopped it immediately. The frequency of the rhythm was influenced by the anesthesia. In these older mice no visual receptive fields could be mapped, but in a few tectal recordings it was possible to suppress the maintained activity by diffuse, very intense illumination. As in normal mice, no auditory or somatosensory responses were observed in the visual cortex or upper tectal layers. In recordings from tectum before the age of three weeks retinotopic topography and receptive fields were normal. By day 24 no receptive fields could be recorded from parts of the tectum representing the central 90--100 degrees of the visual field, whereas within a peripheral ring responses were still roughly normal under photopic conditions. Over the following four months these peripheral responses faded away slowly. Incremental thresholds, especially in the scotopic range, were elevated, rising slowly to unmeasurable values. Similarly during dark adaptation the thresholds fell to values several log units above those reached in normal mice; these values of dark adapted thresholds in rd mice rose with age. This is consistent with morphological changes known to occur in the retina as a consequence, of the rd mutation the rods degenerating before the cones.

Cyclic nucleotide metabolism in solid tumor tissues

The examination of the regulation of the system of 3'-5' cyclic nucleotide monophosphates has only begun in cancer tissues. In human cancers, these studies are notably non-existent. However, in animal cancers, especially the Morris hepatomas, enough data has been gathered that, while risky, certain trends seem to begin to appear. Cyclic AMP is constant or lowered, while cyclic GMP is elevated in the fast growing hepatomas. Regulation of adenylate cyclase by protein hormones is reduced, while regulation by epinephrine may be increased. Binding of glucagon is decreased in the fast growing hepatomas. Guanylate cyclase, while being predominantly cytoplasmic in the normal liver, is predominantly membrane bound in the tumors. The liver enzyme is also readily stimulated by several chemical carcinogens. The cyclic GMP phosphodiesterases are decreased in these tumors; while the cAMP phosphodiesterases are increased. Although the cyclic nucleotide dependent protein kinases (histone as substrate) are altered in the hepatomas, observations of unique cyclic nucleotide binding proteins or cAMP independent protein kinases in cancer tissues may be of even greater significance for the development of or the maintenance of the neoplastic state of cells.

Laser induced phagocytosis in the pigment epithelium of the Hunter dystrophic rat

The retinae of 14-day-old Hunter dystrophic rats have been subjected to low-energy irradiation by a pulsed ruby laser. Fifteen days after exposure, pigment epithelial cells had proliferated and repopulated the irradiated areas. In all such areas the subretinal photoreceptor debris had been reduced or lost.

Cyclic nucleotide phosphodiesterases in uterine development

Activities of cyclic nucleotide phosphodiesterase were studied in rat uterus as a function of age, DNA and protein content. Linear kinetics were observed for uterine homogenate cyclic GMP (cGMP) phosphodiesterase activity, but anomalous double-reciprocal plots, suggestive of multiple enzyme forms, were observed for cyclic AMP (cAMP) hydrolysis, cAMP phosphodiesterase was therefore measured at high and low substrate concentrations, 200 muM and 0.25 muM cAMP, respectively, to approximate multiple enzyme activities. Based upon total organ content, the total cAMP and cGMP phosphodiesterase activities increased throughout uterine development, from 5-50 days of age. On the same basis, the apparent low KM cAMP phosphodiesterase increased only between days 5 and 15 and showed no significant increase between days 15 and 50. On the other hand, specific activities of an apparent low KM cAMP phosphodiesterase, expressed per mg of protein or per mug of DNA, showed a marked reduction in activity between 30 and 50 days of age. Chronic administration of 17beta-estradiol to immature rats increased their uterine protein content and decreased the specific activity of the apparent low KM cAMP phosphodiesterase. In another estrogen target tissue, the anterior pituitary, protein and DNA content also increased during development but no changes in specific activities of cyclic nucleotide phosphodiesterase were noted. These results suggest the possible participation of cyclic nucleotide phosphodiesterases in the induction of uterine growth and development by ovarian hormones.