ABSTRACT
Cone photoreceptors in the murine retina are patterned by dorsal repression and ventral activation of S opsin. TR beta 2, the nuclear thyroid hormone receptor beta isoform 2, regulates dorsal repression. To determine the molecular mechanism by which TR beta 2 acts, we compared the spatiotemporal expression of TR beta 2 and S opsin from embryonic day (E) 13 through adulthood in C57BL/6 retinae. TR beta 2 and S opsin are expressed in cone photoreceptors only. Both are transcribed by E13, and their levels increase with cone genesis. TR beta 2 is expressed uniformly, but transiently, across the retina. mRNA levels are maximal by E17 at completion of cone genesis and again minimal before P5. S opsin is also transcribed by E13, but only in ventral cones. Repression in dorsal cones is established by E17, consistent with the occurrence of patterning during cone cell genesis. The uniform expression of TR beta 2 suggests that repression of S opsin requires other dorsal-specific factors in addition to TR beta 2. The mechanism by which TR beta 2 functions was probed in transgenic animals with TR beta 2 ablated, TR beta 2 that is DNA binding defective, and TR beta 2 that is ligand binding defective. These studies show that TR beta 2 is necessary for dorsal repression, but not ventral activation of S opsin. TR beta 2 must bind DNA and the ligand T3 (thyroid hormone) to repress S opsin. Once repression is established, T3 no longer regulates dorsal S opsin repression in adult animals. The transient, embryonic action of TR beta 2 is consistent with a role (direct and/or indirect) in chromatin remodeling that leads to permanent gene silencing in terminally differentiated, dorsal cone photoreceptors.
Subject(s)
Retinal Cone Photoreceptor Cells/embryology , Retinal Cone Photoreceptor Cells/metabolism , Rod Opsins/metabolism , Thyroid Hormone Receptors beta/metabolism , Animals , Body Patterning , Female , Gene Expression Regulation, Developmental , Gene Silencing , Male , Mice , Mice, Inbred C57BL , Mice, Knockout , Mice, Transgenic , Pregnancy , RNA, Messenger/genetics , RNA, Messenger/metabolism , Retinal Cone Photoreceptor Cells/growth & development , Rod Opsins/genetics , Thyroid Hormone Receptors beta/deficiency , Thyroid Hormone Receptors beta/genetics , Triiodothyronine/metabolismABSTRACT
Mice express S and M opsins that form visual pigments for the detection of light and visual signaling in cones. Here, we show that S opsin transcription is higher than that of M opsin, which supports ultraviolet (UV) sensitivity greater than midwavelength sensitivity. Surprisingly, most cones coexpress both S and M opsins in a common cone cell type throughout the retina. All cones express M opsin, but the levels are graded from dorsal to ventral. The levels of S opsin are relatively constant. However, in the far dorsal retina, S opsin is repressed stochastically, such that some cones express M opsin only. These observations indicate that two different mechanisms control M and S opsin expression. We suggest that a common cone type is patterned across the retinal surface to produce phenotypic cone subtypes.
Subject(s)
Retina/metabolism , Retinal Cone Photoreceptor Cells/metabolism , Rod Opsins/biosynthesis , Animals , Cell Count , Immunohistochemistry , In Situ Hybridization , Mice , Mice, Inbred BALB C , Mice, Inbred C57BL , Microscopy, Confocal , Molecular Sequence Data , Organ Specificity , Protein Isoforms/biosynthesis , Protein Isoforms/genetics , RNA, Messenger/genetics , RNA, Messenger/metabolism , Retina/cytology , Retinal Cone Photoreceptor Cells/cytology , Retinal Rod Photoreceptor Cells/cytology , Retinal Rod Photoreceptor Cells/metabolism , Rod Opsins/genetics , Species SpecificityABSTRACT
We mapped the distribution of neuregulin and its transmembrane precursor in developing, embryonic chick and mouse spinal cord. Neuregulin mRNA and protein were expressed in motor and sensory neurons shortly after their birth and levels steadily increased during development. Expression of the neuregulin precursor was highest in motor and sensory neuron cell bodies and axons, while soluble, released neuregulin accumulated along early motor and sensory axons, radial glia, spinal axonal tracts and neuroepithelial cells through associations with heparan sulfate proteoglycans. Neuregulin accumulation in the synaptic basal lamina of neuromuscular junctions occurred significantly later, coincident with a reorganization of muscle extracellular matrix resulting in a relative concentration of heparan sulfate proteoglycans at endplates. These results demonstrate an early axonal presence of neuregulin and its transmembrane precursor at developing synapses and a role for heparan sulfate proteoglycans in regulating the temporal and spatial sites of soluble neuregulin accumulation during development.
Subject(s)
Embryonic Development , Gene Expression Regulation, Developmental/genetics , Glycoproteins/metabolism , Muscle Development , Spinal Cord/growth & development , Amino Acid Sequence , Animals , Chick Embryo , Extracellular Matrix/metabolism , Heparan Sulfate Proteoglycans/metabolism , Immunochemistry , In Situ Hybridization , Microscopy, Electron , Molecular Sequence Data , Neuregulins , RNA Splicing/genetics , RNA, Messenger/geneticsABSTRACT
Yield losses in wheat (Triticum aestivum) caused by leaf rust were evaluated in cultivar trials at five locations in Mississippi over a 4-year period from 1986 through 1989. Different levels of disease developed in the various trials over the 4-year period. There was no significant interaction between location and cultivar when yield data were collected from sites in the north and central areas of the state. A model derived from data for eight cultivars at two locations showed a negative linear relationship between yield and leaf rust. Total grain yield was reduced by 1% for each 1% increase in rust when the percentage flag leaf area covered by pustules was assessed visually at Feekes stage 11.1. Using this model, and rust ratings from three additional locations, predicted yields were statistically similar to recorded yields.
