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According to historical records of transatlantic slavery, traders forcibly deported an estimated 12.5 million people from ports along the Atlantic coastline of Africa between the 16th and 19th centuries, with global impacts reaching to the present day, more than a century and a half after slavery's abolition. Such records have fueled a broad understanding of the forced migration from Africa to the Americas yet remain underexplored in concert with genetic data. Here, we analyzed genotype array data from 50,281 research participants, which-combined with historical shipping documents-illustrate that the current genetic landscape of the Americas is largely concordant with expectations derived from documentation of slave voyages. For instance, genetic connections between people in slave trading regions of Africa and disembarkation regions of the Americas generally mirror the proportion of individuals forcibly moved between those regions. While some discordances can be explained by additional records of deportations within the Americas, other discordances yield insights into variable survival rates and timing of arrival of enslaved people from specific regions of Africa. Furthermore, the greater contribution of African women to the gene pool compared to African men varies across the Americas, consistent with literature documenting regional differences in slavery practices. This investigation of the transatlantic slave trade, which is broad in scope in terms of both datasets and analyses, establishes genetic links between individuals in the Americas and populations across Atlantic Africa, yielding a more comprehensive understanding of the African roots of peoples of the Americas.

Publisher Summary This chapter discusses imaging ion channel dynamics in living neurons by fluorescence microscopy. The distribution of ion channels and receptors over the neuronal surface is important for the receipt of incoming synaptic inputs and for the integration of these inputs. Most voltage-gated and ligand-gated ion channels have nonhomogeneous distributions in the neuronal membrane; many are restricted to dendritic, axonal, or somatic domains and are further localized within these domains to regions such as dendritic spines, nodes of Ranvier, or synaptic junctions. Determining where and how ion channels are distributed and maintained is important for a variety of reasons. Ion channels in growth cones have a role in neurite outgrowth mechanisms; they are obligatory for synaptic transmission and are required for amplification of neurotransmitter signals in the postsynaptic membrane. Changes in ion-channel distributions are an important aspect in development and plasticity. Several neurological disorders, including multiple sclerosis, are characterized by a change in ion-channel distribution, which is partially responsible for the clinical manifestations of the disease. Fluorescence techniques are invaluable in the study of ion-channel and receptor distributions and dynamics. Fluorescence microscopy has extremely high sensitivity, the lower limit being the ability to detect a single fluorophore under optimal conditions. Fluorescence measurements are specified by the wavelengths of emission and excitation.

Publisher Summary Acetylcholine (ACh) is stored by synaptic vesicles at about 100-fold higher concentration than present in the cytoplasm. As vesicular ACh is free in solution, energy input is required to establish the gradient of concentration. This is accomplished in a process having at least two macromolecular components that reside in the vesicular membrane. The first component is a proton-pumping ATPase known as a V-type ATPase. It pumps protons into the synaptic vesicle, thus acidifying the vesicle core to about pH 5.4. The enzyme is found in the vacuolar-type intracellular organelles, and it is evolutionally related to the mitochondria1 ATPase. The second component is the ACh transporter (AChT). It exchanges one or more vesicular protons for cytoplasmic ACh, thus accomplishing secondary active transport of ACh. The ACh exhibits a transport Michaelis dissociation constant (KM) of about 0.3 mM, which is less than the 4 mM that can be estimated for the concentration of ACh in the cytoplasm. Proton-exchanging transporters appear to account for vesicular storage of all of the classical neurotransmitters. As a class, these transporters are poorly characterized. A structure-activity study has demonstrated that the potency of vesamicol analogues, as assessed by inhibition of active transport, is highly dependent upon the structure of the analogue. This chapter reports the results of the recent ligand-interaction experiments that were directed toward making a choice between models 1 and 2, and toward the identification of the macromolecular structures of the AChT and VR.