A ribosomal DNAâ€"polymerase chain reaction (PCR) method has been de veloped for species identification of individuals of the five most widespread members of the Anopheles gambiae complex, a group ofmorphologically indistinguishable sibling mos quito species that includes the major vectors of malaria in Africa. The method, which is based on species-specific nucleotide sequences in the ribosomal DNA intergenic spacers, may be used to identify both species and interspecies hybrids, regardless of life stage, using either extracted DNA or fragments of a specimen. Intact portions of a mosquito as small as an egg or the segment of one leg may be placed directly into the PCR mixture for amplification and analysis. The method uses a cocktail of five 20-base oligonucleotides to identify An. gambiae,An. arabiensis, An. quadriannnulatus, and eitherAn. melasinwestern Africa or An. me/as in eastern and southern Africa. The Anopheles gambiae complex is a group of six morphologically indistinguishable yet genet ically and behaviorally distinct mosquito species that vary dramatically in their importance as vectors ofmalaria in Africa.' 2 As many as three and possibly four species may be sympatric in some regions, and at least two occur in most malaria-endemic areas. Current epidemiologic assumptions about their malaria transmission biology are based on an extensive but scientifi cally compromisedliterature in which the species reported, A. gambiae sensu lato, was often a mix ture of at least two members of this complex. Several methods for identifying the species of individual specimens in this complex have been developed, including allozyme analysis, polytene chromosome banding patterns, high-perfor mance liquid chromatography of cuticular hy drocarbons, and hybridization with DNA probes that are either species-specific or reveal species specific restriction enzyme fragments.37 Only the eace&I fnr evntheci7ina the nlienniitlentirle nrinierc ucM in this work, and D. Mills Hamm for constructing the 529

Although many genes are known to be critical for early hematopoiesis in the embryo, it remains unclear whether distinct regulatory pathways exist to control hematopoietic specification versus hematopoietic stem cell (HSC) emergence and function. Due to their interaction with key regulators of hematopoietic commitment, particular interest has focused on the role of the ETS family of transcription factors; of these, ERG is predicted to play an important role in the initiation of hematopoiesis, yet we do not know if or when ERG is required. Using in vitro and in vivo models of hematopoiesis and HSC development, we provide strong evidence that ERG is at the center of a distinct regulatory program that is not required for hematopoietic specification or differentiation but is critical for HSC maintenance during embryonic development. We show that, from the fetal period, ERG acts as a direct upstream regulator of Gata2 and Runx1 gene activity. Without ERG, physiological HSC maintenance fails, leading to the rapid exhaustion of definitive hematopoiesis.

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The six Afrotropical species of mosquitoes comprising the Anopheks gambiae complex include the most efficient vectors of malaria in the world as well as a nonvector species. The accepted interpretation of evolutionary relationships among these species is based on chromosomal inversions and suggests that the two principal vectors, A. gambiae and Anopheks arabiensis, are on distant branches of the phylogenetic tree. However, DNA sequence data indicate that these two species are sister taxa and suggest gene flow between them. These results have important implications for malaria control strategies involving the replacement of vector with nonvector populations.