Drosophila thoracic mechanosensory bristles originate from cells that are singled out from 'proneural' groups of competent epithelial cells. Neural competence is restricted to individual sensory organ precursors (SOPs) by Delta/Notch-mediated 'lateral inhibition', whereas other cells in the proneural field adopt an epidermal fate. The precursors of the large macrochaetes differentiate separately from individual proneural clusters that comprise about 20-30 cells or as heterochronic pairs from groups of more than 100 cells, whereas the precursors of the small regularly spaced microchaetes emerge from even larger proneural fields. This indicates that lateral inhibition might act over several cell diameters; it was difficult to reconcile with the fact that the inhibitory ligand Delta is membrane-bound until the observation that SOPs frequently extend thin processes offered an attractive hypothesis. Here we show that the extension of these planar filopodia--a common attribute of wing imaginal disc cells--is promoted by Delta and that their experimental suppression reduces Notch signalling in distant cells and increases bristle density in large proneural groups, showing that these membrane specializations mediate long-range lateral inhibition.
We examined the topography of the lateral line primary projection in zebrafish larvae by double labeling. The projections of two identified neuromasts of the posterior lateral line are seen as two separate sets of fibers that show reproducible spatial relationships: the projection of the anterior neuromast is always ventrolateral to that of a more posteriorly located neuromast. The same rule applies to the projection of anterior lateral line neuromasts. The position of the neuromasts along the antero posterior axis of the fish therefore is represented in the central projection of the sensory neurons. This somatotopy is similar to, and may be at the origin of, the tonotopic projection of the cochlear hair cells in mammals.The coevolution of sense organs and a central processing system that can handle the information they provide is a major problem in developmental neurobiology. One case in point is the development of the auditory system. The generation of an organ capable of discriminating frequencies, such as the mammalian cochlea, would make little sense if the sensory axons were to project indiscriminately in the brain. Indeed there is a marked somatotopy in the central projection of the primary auditory neurons (1). It raises the question of the origin of this somatotopy, and whether it developed before the emergence of a cochlear system. The auditory system is evolutionarily and developmentally related to the lateral line of fishes and amphibians, and indeed it has been suggested that the former is derived from the latter. It therefore is conceivable that the emergence of a topographic representation in the auditory projection finds its roots in a similar representation of the mechanosensory lateral line system.The mechanosensory lateral line is a water displacement detecting system (2, 3) and is thought to mediate a sense of ''distant touch'' (4) whereby the animal is able to perceive and localize movements in its vicinity, within a radius of the order of its own body length. Depending on the ecological niche of the animal, the lateral line is associated with various behavioral responses such as prey detection, obstacle or predator avoidance, and schooling behavior.The peripheral sensory organs of the lateral line, the neuromasts, consist of mechanosensory hair cells surrounded by support cells, much like the organs of the inner ear. They can be enclosed in pouches, canals, or vesicles, but their simplest form is superficial. The base of the hair cells makes synapses on the peripheral process of bipolar sensory neurons located in a cranial ganglion. One ganglion, located anterior to the ear, conveys the sensory information gathered by the head neuromasts (anterior lateral line system), while a second ganglion behind the ear innervates the trunk and tail neuromasts (posterior lateral line system). The axons from the two ganglia enter the hindbrain at different rostro-caudal levels; they then bifurcate and extend anteriorly and posteriorly in the dorsal hindbrain.In adult bony fishes the central proje...
Comparison of 60 human immunoglobulin variable lambda (IGLV) sequences allowed us to define seven subgroups designated V lambda I to V lambda VII. We demonstrate that all lambda proteins sequenced so far fall into the subgroups I, II, III and VI, and that the lambda regions previously assigned to subgroups IV and V belong, in fact, to subgroups III and II, respectively. Four sequences not belonging to any of the subgroups I, II, III and VI define the new subgroups IV, V and VII. Interestingly, these subgroups show a higher homology to rabbit or mouse V lambda genes than to the other human V lambda subgroups. By comparison of the proteins either with the sequences deduced from the germ-line genes or with the consensus sequences, the rate of amino acid changes due to somatic mutations or allelic variations was evaluated in several lambda proteins. Framework and complementarity-determining regions of the human IGLV genes and proteins were delineated. Alignment of the lambda sequences shows that functional V-J rearrangement occurs, with or without deletion of nucleotides encoding one or two amino acids at the 3' end of the V gene. Diversity of the third complementarity-determining region is due to somatic mutations and to flexible V-J junction, but there is no evidence of N-diversity in the human lambda locus.
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.
hi@scite.ai
10624 S. Eastern Ave., Ste. A-614
Henderson, NV 89052, USA
Copyright © 2024 scite LLC. All rights reserved.
Made with 💙 for researchers
Part of the Research Solutions Family.