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To identify genes necessary for establishing connections in the Drosophila sensory nervous system, we designed a screen for mutations affecting development of the larval visual system. The larval visual system has a simple and stereotypic morphology, can be recognized histologically by a variety of techniques, and is unnecessary for viability. Therefore, it provides an opportunity to identify genes involved in all stages of development of a simple, specific neuronal connection. By direct observation of the larval visual system in mutant embryos, we identified 24 mutations affecting its development; 13 of these are larval visual system-specific. These 13 mutations can be grouped phenotypically into five classes based on their effects on location, path or morphology of the larval visual system nerves and organs. These mutants and phenotypic classifications provide a context for further analysis of neuronal development, pathfinding and target recognition.

The profile of cardiologist Herbert Benson by Wade Roush (Research News, [18 Apr., p. 357][1]) and the review by Irwin and Jack Tessman of his book Timeless Healing in the same issue (p. 369) devote extensive discussion to Benson’s intentions to demonstrate the power of belief in health and healing. One might also consider the pioneering work in this field more than a century ago by the biometrician Sir Francis Galton ([1][2]). Although his proposals were refused to directly test the efficacy of prayer for patients in one wing of a hospital as compared with those not prayed for in another wing, Galton performed a statistical analysis of the question from existing data by considering the effect of collective prayer on the life expectancy of different classes of English society. As summarized by Haldane ([2][3])He considered that of all classes of society in England those most prayed for were the sovereigns and the children of the clergy. If prayer is effective they should live appreciably longer than other persons exposed to similar risks of death. So kings were compared with lords, and the children of the clergy with those of other professional men. The conclusion to which his numbers led was that these much-prayed-for persons had slightly shorter lives than those with whom he compared them. Galton also determined the frequency with which ships carrying missionaries experienced disaster at sea and compared this with the frequency of disaster experienced by other ships. He found that missionary ships sank with a frequency and loss of life only slightly greater than that of less-blessed ships. The important conclusion reached by Haldane, and one perhaps important to gain also from Benson’s work, is that in neither analysis were the differences great enough to make it probable that prayers have any harmful effect. 1. [↵][4]F. Galton, Fortnight Rev. 12 , 125 (1872). 2. [↵][5]J.B.S. Haldane, in Possible Worlds and Other Papers (Chatto and Windus, London, 1928), pp. 237–252. # {#article-title-2} Benson needs to include a group of coronary bypass patients who know they are not being prayed for, along with the group who think they might be being prayed for and those who know they are being prayed for. The controls could then be coronary bypass atheists who adamantly doubt the efficacy of prayer, even after a good outcome. The controls required of this study would thus never benefit, and the others always would. By Benson’s protocol, prayer always works, it’s probably working right now, and that’s why we’re all not a whole lot sicker. # {#article-title-3} Debating whether humans are “hardwired for prayer” misses the point. Whether an individual copes with the dilemma of mortality by using prayer, exercise, a walk in the countryside, or the enjoyment of higher math and astrophysics, the end result can be the same. From an evolutionary perspective, individuals who do not give up hope would be expected to be more fecund. [1]: /lookup/doi/10.1126/science.276.5311.357 [2]: #ref-1 [3]: #ref-2 [4]: #xref-ref-1-1 "View reference 1 in text" [5]: #xref-ref-2-1 "View reference 2 in text"

Mutations in the disco (disconnected) gene prevent the establishment of stable connections between the larval optic nerves, the Bolwig's nerves, and their target cells in the brain during embryonic development. The failure of this initial connection is associated with aberrant development of the optic lobes which are largely degenerate in the mutant adult fly. In order to understand the role of disco in establishing this connection, we isolated and characterized the disco gene. A 22 kb DNA fragment can completely rescue the mutant phenotype. A single transcript, 2.9 kb in length, is found in this region and is expressed throughout development of the fly. We determined the nucleotide sequence of the disco gene to be unique when compared with sequences in a number of databases. The predicted amino acid sequence contains a region with similarity to the consensus established for the zinc finger motif. Mobilization of a P-element inserted near the gene resulted in the deletion of the 5' end of the gene and produced flies indistinguishable from those carrying the disco allele.

LIM-homeodomain transcription factors (LIM-HD) regulate expression of genes that pattern the body and generate cell specificity during development in invertebrates and vertebrates. It is especially interesting that most are expressed in and participate in the development of the nervous system. LIM-HD proteins are themselves regulated by both intramolecular and intermolecular interactions mediated by the LIM domains. LIM domains positively regulate LIM-HD activity by promoting protein-protein interactions that allow cooperative binding to regulatory regions of tissue-specific promoters. They also negatively regulate LIM-HD activity, possibly by preventing HD association with DNA. Interaction of LIM domains with other proteins relieves this interference, permitting DNA binding and providing a mechanism for refining LIM-HD activity. The recurrence of LIM-HD proteins in fundamental developmental processes emphasizes the importance of their function and regulation and provides an opportunity to identify mechanisms and molecules underlying patterning and cell specification.