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. 171:240-2414, 1989). Mutants with transposon insertions in this regulatory locus were used to construct a hybridization probe which was used in this study to Luminescent bacteria are widespread in the marine environment, where they exist planktonically and as parasites and light organ symbionts. Light production by symbiotic bacteria living in association with higher organisms may serve to attract prey, for intraspecies communication, or to escape from predators (34). Luminescence could also function to provide a direct benefit to the bacteria. One possibility is that the luminescence system is used as a terminal oxidase when the cytochrome electron transport system cannot be synthesized (low iron availability) or cannot function (low oxygen tension) (26). Luciferase, a mixed function oxidase consisting of a and I subunits, catalyzes the emission of light (Fig. 1). In the generation of light, luciferase oxidizes a reduced flavin, FMNH2, and a longchain fatty aldehyde producing oxidized flavin and the corresponding fatty acid (22). A fatty acid reductase unique to the bioluminescence system functions to synthesize or recycle the aldehyde substrate. Expression of cloned genes for luciferase and fatty acid reductase is sufficient for the production of light in a variety of nonluminous bacterial hosts (12, 37), so functions that supply reduced flavin and precursors of the fatty aldehyde substrate are apparently not unique to the bioluminescence system.Light production by most species of luminous bacteria is strongly influenced by the density of the cell culture. Light emission per cell can be as much as 1,000-fold higher in dense cultures than in dilute cultures. Density-dependent regulation of luminescence has been investigated most thoroughly with the light organ symbiont Vibrio fischeri (9,25,33 luminescence. Autoinducer from V. fischeri has been shown to be N-(P-ketocaproyl)homoserine lactone (10). The genes (lux) necessary for light production in recombinant hosts have been cloned from V. fischeri (strain MJ-1) on one 9-kilobase (kb) fragment of DNA (12, 13). This fragment contains genes encoding regulatory functions and the luciferase and fatty acid reductase enzymes. Regulation of light production in recombinant Escherichia coli containing lux genes mirrored that observed in V. fischeri, so the refined genetic techniques developed for E. coli have been used to explore the molecular basis of luminescence control. It is clear from these studies that autoinducer controls light production by inducing transcription of the lux operon encoding the enzymes for luminescence.Expression of lux in Vibrio harveyi, as in V. fischeri, is dependent on the density of the cell culture, but the luminescence systems of these species differ substantially with respect to the nature of the autoinducer substances and the organization of lux genes. The autoinducer of V. fischeri, N-(,B-ketocaproyl)homoserine lactone, is produced only by V. fischeri and elicits a response only in V. fischeri. The autoinducer from V. harveyi is dif...

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Mutagenesis with transposon mini-Mulac was used to identify loci containing genes for bioluminescence (lux) in the marine bacterium Vibyio harveyi. Transposon insertions which resulted in a Lux-phenotype were mapped to two unlinked regions of the genome. Region I contained the luxCDABE operon which was previously shown to encode the enzymes luciferase and fatty acid re-ductase, which are required for light production. The other locuis, region II, which was identified for the first time in this study, appeared to have a regulatory function. In Northern blot analysis of mRNA from mutants with defects in this region, no transcription from the luxCDABE operon could be detected. Strains with transposon-generated luxc::lacZ gene fusions were used to analyze control of the transcription of these regions. Expression of luminescence in the wild type was strongly influenced by the density of the culture, and in strains with the lacZ indicator gene coupled to the luxCDABE operon, 8-gialactosidase synthesis was density dependent. So, transcription of this operon is responsive to a density-seiising mechanism. However, I-galactosidase synthesis in strains with lacZ fused to the region II transcriptional unit did not respond to cell density. The organization and regulation of the lux genes of V. harveyi are discussed, particularly with regard to the contrasts observed with the lux system of the fish light-organ symbiont Vibrio fischeri.Luminpscent bacteria are common in the marine environment, Where they exist planktonically and as parasites and light-organ symbionts. Light production by symbiotic bacteria living in association with higher organisms may be used to attract prey, for intraspecies communication, or to escape from predators (24). Luminescence could function to provide a direct benefit to the bacteria. Light emitted by large aggregations of bacteria may attract feeders which ingest the bacteria into the nutrient-rich environment of the gut tracts. Another possibility is that the luminescence system is used as a terminal oxidase when the cytochrome electron transport system cannot be synthesized (low iron availability) or cannot function (low oxygen tension) (15). Luciferase, a mixed-function oxidase corisisting of ox and P subunits, catalyzes the emission of light (Fig. 1). In the generation of light, luciferase oxidizes a reduced flavin, FMNH2, and a long-chain fatty aldehyde, producing oxidized flavin and the corresponding fatty acid (30). A fatty acid reductase unique to the bioluminescence system functions to synthesize or recycle the aldehyde substrate. Expression of cloned genes for luciferase and fatty acid reductase is sufficient for the production of light in a variety of nonluminous bacterial hosts (5, 26), so functions which supply reduced flavin and precursors of the fatty aldehyde substrate are apparently not unique to the bi?luminescence system. Light pr.oduction by most species of luminous bacteria is strongly influenced by the density of the cell culture. Light emission per cell can be as much as ...

In Nissl-stained preparations of the cochlear nucleus there are nine recognizable cell types. These cells are born during three periods of histogenesis prenatally. On gestation days 10.0, 10.5, and 11.0 the pyramidal, giant, and dark-staining cells are born. The spherical, globular, multipolar, and horizontal cells are formed on gestation days 12.0, 12.5, and 13.0 and small cells follow on gestation day 14.5. The onset of granule cell formation is gestation day 14.5 continues to birth on gestation day 19. At birth, and for at least the first 2 postnatal weeks, glial cells are born. There are no regional gradients in cell birth dates, cells from all birth dates being intermixed. Cell birth proceeds in an orderly sequence that is related only to cell size. Although there were no apparent spatiotemporal patterns, some clustering of labeled cells was evident. These observations do not support the hypothesis that Golgi Type I cells precede Golgi Type II cells in their order of birth since both large and small neurons project beyond the nucleus. There is, nonetheless, a sequential pattern in the onset of cell birth for the auditory system, with cochlear nucleus neurons preceding cochlear neurons.