Retinoid-related orphan receptor ␣ (ROR␣) is a member of the nuclear receptor superfamily. To study its physiological role we generated null-mutant mice by targeted insertion of a lacZ reporter gene encoding the enzyme ␤-galactosidase. In heterozygous ROR␣ ؉/؊ mice we found ␤-galactosidase activity, indicative of ROR␣ protein expression, confined to the central nervous system, skin and testis. In the central nervous system, the ROR␣ gene is expressed in cerebellar Purkinje cells, the thalamus, the suprachiasmatic nuclei, and retinal ganglion cells. In skin, ROR␣ is strongly expressed in the hair follicle, the epidermis, and the sebaceous gland. Finally, the peritubular cells of the testis and the epithelial cells of the epididymis also strongly express ROR␣. Recently, it was reported that the ataxic mouse mutant staggerer (sg͞sg) is caused by a deletion in the ROR␣ gene. The analysis of the cerebellar and the behavioral phenotype of homozygous ROR␣ ؊/؊ mice proves identity to sg͞sg mice. Although the absence of ROR␣ causes dramatic developmental effects in the cerebellum, it has no apparent morphological effect on thalamus, hypothalamus, and retina. Similarly, testis and skin of ROR␣ ؊/؊ mice display a normal phenotype. However, the pelage hair of both sg͞sg and ROR␣ ؊/؊ is significantly less dense and when shaved shows reluctance to regrow.Nuclear receptors form a structurally related superfamily of ligand-activated transcription factors (1). They are involved in several aspects of vertebrate physiology, such as development and homeostasis. Important examples are the steroid hormone receptors that regulate, in a ligand-dependent manner, specific sets of responding genes. The retinoid-related orphan nuclear receptor (ROR) ␣ (2, 3), ROR␤ (4), and ROR␥ (5) constitute a subfamily of nuclear receptors that bind to DNA both as monomers and dimers. Distribution of ROR␣ mRNA suggests that this receptor is widely expressed and functions in several organs including brain, heart, liver, lung, and testis; highest levels were found in peripheral blood leukocytes and skin (M.B.-A., unpublished data). ROR␣ exists in four splicing isoforms: ROR␣1-4. They display different N-terminal domains causing different DNA binding site preferences (3), and they display differential expression profiles: in the thalamus there is only ROR␣1 mRNA; ROR␣4 (ϭRZR␣) (2) transcripts are predominant in leukocytes and skin; ROR␣2 and ROR␣3 transcripts are exclusively detected in testis; and in the remaining tissues including the cerebellum there is a mixture of ROR␣1 and ROR␣4 transcripts (M.B.-A., unpublished results). In the central nervous system (CNS) ROR␣ mRNA localizes to the cerebellar Purkinje cells (PCs), various thalamic nuclei, and, during development, to other brain areas (6, 7). To study the physiological role of this orphan receptor we generated ROR␣ null-mutant mice by gene targeting. In the course of this work the genetic basis of the staggerer (sg) mutation in mouse was identified by positional cloning as a deletion in the R...

Climbing fiber (CF)-Purkinje cell (PC) relationship were studied electrophysiologically on the cerebellum of 8 to 15 day old rats. Some animals were rendered agranular by x-irradiation from birth; some others were treated with 3-acetyl pyridine 3 days before study to selectively destroy the CF. Unitary extracellular recordings in 8-9 day old normal rats revealed that more than 50% of the PC units each exhibited either two types of all-or-none climbing fiber responses (CFR) or stepwise graded CFRs. The other PC units only presented one type of all-or-none CFR. These activities were entirely mediated via CF since they persisted at the same age in x-irradiated rats, but were absent in animals treated with 3-acetyl pyridine. Interaction experiments were performed between juxtafastigial and Inferior Olive stimulations on 49 PC units in 8-9 day old normal rats. Collisions between impulses set up in CFs were disclosed in 21 out of the 24 PCs which exhibited only one type of CFR. In the three others and in each of the 25 PCs that displayed two types of all-or-none CFRs, or CFRs graded by steps, no collision was detected. Moreover intracellular recordings of epsp's mediated via CFs in PCs of 8-9 day old normal rats revealed that they frequently fluctuated in stepwise fashion. These results demonstrate that in the immature rat more than 50% of PCs are each innervated by at least two distinct CFs; later on, the disappearance of the supernumerary synapses between CF and PC leads, as early as day 15, to the one-to-one relationship between CF and PC.

In many instances, the establishment of highly specific neuronal connections during development results from the rearrangement of axonal projections through the trimming of exuberant collaterals or the elimination of functional synapses or both. Although the involvement of the N-methyl D-aspartate (NMDA) subtype of the glutamate receptor has been demonstrated in the shaping of axonal arbors, its participation in the process of selective stabilization of synapses remains an open issue. In this study, the effects of chronic in vivo application of D,L-2-amino-5-phosphonovaleric acid (D,L-APV), a selective antagonist of the NMDA receptor, on the synapse elimination process that takes place in the developing cerebellum of the rat have been analyzed. D,L-APV treatment prevented the regression of supernumerary climbing fiber synapses in 49 percent of the recorded Purkinje cells, while the inactive isomer L-APV was ineffective. Thus, activation of the NMDA receptor is a critical step in the regression of functional synapses during development.

Background-Hypoalphalipoproteinemia is the most common lipoprotein abnormality in patients with coronary artery disease, yet its causes are unknown. Methods and Results-We show that the homozygous staggerer (sg/sg) mutant mouse, which carries a deletion within the nuclear receptor ROR␣ gene, develops severe atherosclerosis when maintained on an atherogenic diet. In addition, sg/sg mice display a profound hypoalphalipoproteinemia, which is associated with decreased plasma levels of the major HDL proteins, apolipoprotein (apo) A-I and apoA-II. This decrease in HDL levels in sg/sg mice is due to lowered apoA-I gene expression in the intestine but not in the liver. ApoA-II gene expression is unaffected. Conclusions-These results suggest that the ROR␣ gene contributes to the plasma HDL level and susceptibility to atherosclerosis. (Circulation. 1998;98:2738-2743.)

No abstract

In Alzheimer disease, a combination of genetic predisposition and environmental factors may contribute to changes in j8-amyloid precursor protein (APP) expression, f3-amyloid peptide deposition, and neuronal loss. Factors such as head injury or acute infection that trigger inflammatory processes may play a crucial role in development of the disease. In the present in vivo study, we showed that, in mouse brain, peripheral stimulation with lipopolysaccharide (LPS) induced a transient increase in the inflammatory cytokine mRNAs (interleukin 1l8 and interleukin 6), followed by changes in expression of APP isoforms in the cerebellum but not in the cerebral cortex. These changes consisted of a decrease in the APP-695 and an increase in the Kunitz protease inhibitor-bearing isoforms (KPI-APP). In the cerebellum of the staggerer mouse mutant, where a severe loss of Purkinje and granule cells occurs, basal mRNA levels of these interleukins were elevated and an increase in the KPI-APP/APP-695 ratio compared to wild-type mice was observed. These abnormalities were further accentuated by LPS stimulation. This study shows that acute and chronic inflammatory processes play an important role in changes in APP expression possibly associated with neurodegeneration.

SYNOPSISRecent research into the developmental elimination of supernumerary synapses has increased understanding of this process. In this review we discuss synapse elimination both at the neuromuscular junction and in the central nervous system, considering some possible underlying mechanisms suggested by recent studies. In addition a well-described example of central nervous system synapse elimination, the climbing fiber-Purkinje cell synapse of the cerebellum, is used to explore the functional significance of synaptic regression during brain development.

The Purkinje cell is a primary organizer in the development of the cerebellum. Purkinje cells may provide positional information cues that regulate afferent innervation, and Purkinje cell target size controls the adult number of afferent olivary neurons and granule cells. While Purkinje cells are necessary for the survival of olivary neurons and granule cells during periods of programmed cell death, little is known about the survival requirements of Purkinje cells in vivo. To determine if Purkinje cells are subject to programmed cell death during development we have analyzed Purkinje cell numbers in two lines of transgenic mice that overexpress a human gene for bcl-2 (Hu-bcl-2). Bcl-2 is a protooncogene that inhibits apoptosis in many cell types. Overexpression of bcl-2 in vitro and in vivo rescues neurons from trophic factor deprivation or naturally occurring cell death. In the mice analyzed in this study, transgene expression is driven by the neuron-specific enolase promoter that is first expressed embryonically in most regions of the brain in one line and postnatally in the second line. We have counted Purkinje cells in three adult control mice, five early overexpressing transgenics, and three late expressing transgenics. The number of Purkinje cells in the Hu-bcl-2 transgenic mice is significantly increased above control numbers, with an increase of 43% in the embryonically overexpressing line and an increase of 27% in the postnatally overexpressing line. Because bcl-2 overexpression has been shown to rescue other neurons from programmed cell death, the increase in Purkinje cell numbers in overexpressing bcl-2 transgenics suggests that Purkinje cells undergo a period of cell death during normal development.