Single-nucleotide polymorphisms in the public domain: how useful are they?

There is a concerted effort by a number of public and private groups to identify a large set of human single-nucleotide polymorphisms (SNPs). As of March 2001, 2.84 million SNPs have been deposited in the public database, dbSNP, at the National Center for Biotechnology Information (http://www.ncbi.nlm.nih.gov/SNP/). The 2.84 million SNPs can be grouped into 1.65 million non-redundant SNPs. As part of the International SNP Map Working Group, we recently published a high-density SNP map of the human genome consisting of 1.42 million SNPs (ref. 3). In addition, numerous SNPs are maintained in proprietary databases. Our survey of more than 1,200 SNPs indicates that more than 80% of TSC and Washington University candidate SNPs are polymorphic and that approximately 50% of the candidate SNPs from these two sources are common SNPs (with minor allele frequency of > or =20%) in any given population.     

The prolactin releasing peptides: RF-amide peptides

Although dopamine is considered the major hypothalamic controller of prolactin release from the anterior pituitary gland, there is evidence that a yet to be discovered prolactin releasing factor (PRF) also exists in brain. Recently, two peptides were isolated, products of the same prohormone, that were reported to have significant prolactin-releasing activity. These peptides, called prolactin releasing peptides, are not accepted by all investigators to be in fact PRFs. Instead, it appears that their widespread distribution in brain and the presence of receptors for the peptides in sites unrelated to neuroendocrine function are the basis for a variety of central nervous system action including activation of the autonomic nervous system. Thus, these peptides may not be PRFs, but instead neuroactive agents that are involved in many brain circuits with divergent functions.     

Deep-sea ecology. Developmental arrest in vent worm embryos

Temperature is a key factor in controlling the distribution of marine organisms and is particularly important at hydrothermal vents, where steep thermal gradients are present over a scale of centimetres. The thermophilic worm Alvinella pompejana, which is found at the vents of the East Pacific Rise (2,500-m depth), has an unusually broad thermotolerance (20-80 degrees C) as an adult, but we show here that the temperature range required by the developing embryo is very different from that tolerated by adults. Our results indicate that early embryos may disperse through cold abyssal water in a state of developmental arrest, completing their development only when they encounter water that is warm enough for their growth and survival.     

Role for sperm in spatial patterning of the early mouse embryo

Despite an apparent lack of determinants that specify cell fate, spatial patterning of the mouse embryo is evident early in development. The axis of the post-implantation egg cylinder can be traced back to organization of the pre-implantation blastocyst. This in turn reflects the organization of the cleavage-stage embryo and the animal-vegetal axis of the zygote. These findings suggest that the cleavage pattern of normal development may be involved in specifying the future embryonic axis; however, how and when this pattern becomes established is unclear. In many animal eggs, the sperm entry position provides a cue for embryonic patterning, but until now no such role has been found in mammals. Here we show that the sperm entry position predicts the plane of initial cleavage of the mouse egg and can define embryonic and abembryonic halves of the future blastocyst. In addition, the cell inheriting the sperm entry position acquires a division advantage and tends to cleave ahead of its sister. As cell identity reflects the timing of the early cleavages, these events together shape the blastocyst whose organization will become translated into axial patterning after implantation. We present a model for axial development that accommodates these findings with the regulative nature of mouse embryos.