Epigenetic Regulation and Environmental Sex Determination in Cichlid Fishes

Studying environmental sex determination (ESD) in cichlids provides a phylogenetic and comparative approach to understand the evolution of the underlying mechanisms, their impact on the evolution of the overlying systems, and the neuroethology of life history strategies. Natural selection normally favors parents who invest equally in the development of male and female offspring, but evolution may favor deviations from this 50:50 ratio when environmental conditions produce an advantage for doing so. Many species of cichlids demonstrate ESD in response to water chemistry (temperature, pH, and oxygen concentration). The relative strengths of and the exact interactions between these factors vary between congeners, demonstrating genetic variation in sensitivity. The presence of sizable proportions of the less common sex towards the environmental extremes in most species strongly suggests the presence of some genetic sex-determining loci acting in parallel with the ESD factors. Sex determination and differentiation in these species does not seem to result in the organization of a final and irreversible sexual fate, so much as a life-long ongoing battle between competing male- and female-determining genetic and hormonal networks governed by epigenetic factors. We discuss what is and is not known about the epigenetic mechanism behind the differentiation of both gonads and sex differences in the brain. Beyond the well-studied tilapia species, the 2 best-studied dwarf cichlid systems showing ESD are the South American genus Apistogramma and the West African genus Pelvicachromis. Both species demonstrate male morphs with alternative reproductive tactics. We discuss the further neuroethology opportunities such systems provide to the study of epigenetics of alternative life history strategies and other behavioral variation.

Gene expression signatures of mating system evolution

The diversity of mating systems among animals is astounding. Importantly, similar mating systems have evolved even across distantly related taxa. However, our understanding of the mechanisms underlying these convergently evolved phenotypes is limited. Here, we examine on a genomic scale the neuromolecular basis of social organization in cichlids of the tribe Ectodini from Lake Tanganyika. Using field-collected males and females of four closely related species representing two independent evolutionary transitions from polygyny to monogamy, we take a comparative transcriptomic approach to test the hypothesis that these independent transitions have recruited similar gene sets. Our results demonstrate that while lineage and species exert a strong influence on neural gene expression profiles, social phenotype can also drive gene expression evolution. Specifically, 331 genes (∼6% of those assayed) were associated with monogamous mating systems independent of species or sex. Among these genes, we find a strong bias (4:1 ratio) toward genes with increased expression in monogamous individuals. A highly conserved nonapeptide system known to be involved in the regulation of social behavior across animals was not associated with mating system in our analysis. Overall, our findings suggest deep molecular homologies underlying the convergent or parallel evolution of monogamy in different cichlid lineages of Ectodini.

Metamorphosis of tangential visual system neurons in Drosophila

To learn about construction of the adult nervous system, we studied the differentiation of imaginal neurons in the Drosophila visual system. OL2-A and OL3 are tangential neurons that display dFMRFa neuropeptide gene expression in adults but not in larvae. The two large OL2-A neurons are generated near the end of the embryonic period and already show morphological differentiation at the start of metamorphosis. The numerous small OL3 neurons are generated postembryonically and first detected later in metamorphosis. The onset of dFMRFa transcription coincides with that of neuropeptide accumulation in OL2-A neurons, but it precedes peptide accumulation in the OL3 neurons by days. Altering each of the five conserved sequences within the minimal 256-bp OL dFMRFa enhancer affected in vivo OL transcriptional activity in two cases: alteration of a TAAT element greatly diminished and alteration of a 9-bp tandem repeat completely abolished OL2-A/OL3 reporter activity. A 46-bp concatamer containing the TAAT element, tested separately, was not active in OL neurons. We propose a model of neuronal differentiation at metamorphosis that features developmental differences between classes of imaginal neurons.

A pdf neuropeptide gene mutation and ablation of PDF neurons each cause severe abnormalities of behavioral circadian rhythms in Drosophila

The mechanisms by which circadian pacemaker systems transmit timing information to control behavior are largely unknown. Here, we define two critical features of that mechanism in Drosophila. We first describe animals mutant for the pdf neuropeptide gene, which is expressed by most of the candidate pacemakers (LNv neurons). Next, we describe animals in which pdf neurons were selectively ablated. Both sets of animals produced similar behavioral phenotypes. Both sets entrained to light, but both were largely arrhythmic under constant conditions. A minority of each pdf variant exhibited weak to moderate free-running rhythmicity. These results confirm the assignment of LNv neurons as the principal circadian pacemakers controlling daily locomotion in Drosophila. They also implicate PDF as the principal circadian transmitter.

Genetic analysis of the Drosophila ellipsoid body neuropil: organization and development of the central complex

The central complex is an important center for higher-order brain function in insects. It is an intricate neuropil composed of four substructures. Each substructure contains repeated neuronal elements which are connected by processes such that topography is maintained. Although the neuronal architecture has been described in several insects and the behavioral role investigated in various experiments, the exact function of this neuropil has proven elusive. To describe the architecture of the central complex, we study 15 enhancer-trap lines that label various ellipsoid body neuron types. We find evidence for restriction of gene expression that is correlated with specific neuronal types: such correlations suggest functional classifications as well. We show that some enhancer-trap patterns reveal a single ellipsoid body neuron type, while others label multiple types. We describe the development of the ellipsoid body neuropil in wild-type animals and propose developmental mechanisms based on animals displaying structural mutations of this neuropil. The experiments performed here demonstrate the degree of resolution possible from the analysis of enhancer-trap lines and form a useful library of tools for future structure/function studies of the ellipsoid body.

Characterization and cloning of tripeptidyl peptidase II from the fruit fly, Drosophila melanogaster

We describe the characterization, cloning, and genetic analysis of tripeptidyl peptidase II (TPP II) from Drosophila melanogaster. Mammalian TPP II removes N-terminal tripeptides, has wide distribution, and has been identified as the cholecystokinin-degrading peptidase in rat brain. Size exclusion and ion exchange chromatography produced a 70-fold purification of dTPP II activity from Drosophila tissue extracts. The substrate specificity and the inhibitor sensitivity of dTPP II is comparable to that of the human enzyme. In particular, dTPP II is sensitive to butabindide, a specific inhibitor of the rat cholecystokinin-inactivating activity. We isolated a 4309-base pair dTPP II cDNA which predicts a 1354-amino acid protein. The deduced human and Drosophila TPP II proteins display 38% overall identity. The catalytic triad, its spacing, and the sequences that surround it are highly conserved; the C-terminal end of dTPP II contains a 100-amino acid insert not found in the mammalian proteins. Recombinant dTPP II displays the predicted activity following expression in HEK cells. TPP II maps to cytological position 49F4-7; animals deficient for this interval show reduced TPP II activity.

The comparative economic performance of investor-owned chain and not-for-profit hospitals

We examined the differences in the economic performance of 80 matched pairs of investor-owned chain and not-for-profit hospitals in eight states during 1978 and 1980, and considered how their operating strategies might affect their relative success in a more price-conscious market. We found that total charges (adjusted for case mix) and net revenues per case were both significantly higher in the investor-owned chain hospitals, mainly because of higher charges for ancillary services; there were no significant differences between the two groups of hospitals in regard to patient-care costs per case (adjusted for case mix), but the investor-owned hospitals had significantly higher administrative overhead costs; investor-owned hospitals were more profitable; investor-owned hospitals had fewer employees per occupied bed but paid more per employee; investor-owned hospitals had funded more of their capital through debt and had significantly higher capital costs in proportion to their operating costs; and the two groups did not differ in patient mix, as measured by their Medicare case-mix indexes or the proportions of their patients covered by Medicare or Medicaid. We conclude that investor-owned chain hospitals generated higher profits through more aggressive pricing practices rather than operating efficiencies - a result not unexpected in view of past cost-based reimbursement policies. Recent changes in these policies are creating new pressures for cost control and moderation in charges, to which both types of hospitals must adapt. Neither type has a clear-cut advantage in the ability to make the necessary changes.