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Author(s): Jun Wu [1, 2]; Henry T. Greely [3]; Rudolf Jaenisch [4]; Hiromitsu Nakauchi [5, 6]; Janet Rossant [7, 8]; Juan Carlos Izpisua Belmonte (corresponding author) [1] In Greek mythology, [...], Chimaeras are both monsters of the ancient imagination and a long-established research tool. Recent advances, particularly those dealing with the identification and generation of various kinds of stem cells, have broadened the repertoire and utility of mammalian interspecies chimaeras and carved out new paths towards understanding fundamental biology as well as potential clinical applications.

Loxodontomys micropus is a rodent that is widely distributed in Andean and Patagonian Argentina and Chile. This range covers a heterogeneous area that has been influenced by geologic and palaeoclimatic events, such as the glaciations during the Neogene. To investigate the genetic structure, phylogeographic pattern, and biogeographic history of this sigmodontine rodent we analyzed a 801-base-pair fragment of the mitochondrial genome (cytochrome-b gene) of 87 specimens from 24 localities from Argentina and Chile. Results indicate that L. micropus has a shallow genealogy that is geographically structured and is a taxon characterized by an historical population expansion. We discuss the distribution of the genetic variation of L. micropus in relation to population history and the concordance with other codistributed sigmodontine rodents. On the basis of molecular evidence, we suggest that the L. pikumche, corresponding to the second extant species of the genus, could be a junior synonym of L. micropus. DOI: 10.1644/10-MAMM-A-027.1. Key words: Andes, cytochrome b, genetic structure, Loxodontomys pikumche, Patagonia, phylogeography

Food availability and quality in desert habitats are spatially and temporally unpredictable, and animals face periods of food shortage. The golden spiny mouse (Acomys russatus) is an omnivorous desert rodent that does not hoard food, requiring it to withstand such periods by physiological means alone. In response to food restriction, plasma leptin concentrations, core body temperature, and energy expenditure of the spiny mouse decrease significantly after 24 h, and most spiny mice are able to maintain their body mass to ~85% of ad libitum for a prolonged period of time. Both l-day food deprivation and long-term food restriction had a significant effect on body mass and plasma leptin concentrations, which decreased significantly with a high correlation, as well as on the orexigenic agouti-related protein, which increased significantly as a result of the 24-h food deprivation; and on neuropeptide Y (NPY), in which the increase was more pronounced under long-term food restriction. Food restriction and food deprivation had no effect, however, on the anorexigenic pro-opiomelanocortin and cocaine and amphetamine-related transcript. Leptin administration to food-restricted spiny mice did not affect food intake or the rate of decrease in body mass, indicating that it cannot overcome the drive to eat when food is scarce. However, it did result in a significant decrease in NPY levels, and the spiny mice spent less time at low body temperatures compared with PBS-treated golden spiny mice. These results show that in food-restricted golden spiny mice, leptin affects thermogenesis, but not food consumption, and suggest that the thermoregulatory effects of leptin are mediated by NPY. torpor; thermogenesis; Acomys russatus; desert; hypothalamic neuropeptides

Quantitative trait locus (QTL) studies of a skeletal trait or a few related skeletal components are becoming commonplace, but as yet there has been no investigation of pleiotropic patterns throughout the skeleton. We present a comprehensive survey of pleiotropic patterns affecting mouse skeletal morphology in an intercross of LG/J and SM/J inbred strains (N = 1040), using QTL analysis on 70 skeletal traits. We identify 798 singletrait QTL, coalescing to 105 loci that affect on average 7-8 traits each. The number of traits affected per locus ranges from only 1 trait to 30 traits. Individual traits average 11 QTL each, ranging from 4 to 20. Skeletal traits are affected by many, small-effect loci. Significant additive genotypic values average 0.23 standard deviation (SD) units. Fifty percent of loci show codominance with heterozygotes having intermediate phenotypic values. When dominance does occur, the LG/J allele tends to be dominant to the SM/J allele (30% vs. 8%). Over- and underdominance are relatively rare (12%). Approximately one-fifth of QTL are sex specific, including many for pelvic traits. Evaluating the pleiotropic relationships of skeletal traits is important in understanding the role of genetic variation in the growth and development of the skeleton.

The molecular mechanisms of aldosterone-regulated [Na.sup.+] transport are not entirely clear. The goal of this study was to identify aldosterone-induced genes potentially involved in the trafficking of the epithelial [Na.sup.+] channel (ENaC). We report that the transcript levels of melanophilin (MLPH), a protein involved in vesicular trafficking in melanocytes, are rapidly increased by aldosterone in cortical collecting duct (CCD) cells. This effect was near maximal at physiological aldosterone concentrations, indicating that it is mediated by the mineralocorticoid receptor. De novo protein synthesis is not required for the induction of MLPH mRNA by aldosterone. To determine whether this induction has functional consequences on transepithelial [Na.sup.+] current, we generated clonal CCD cell lines that express a tetracycline-inducible MLPH. Induction of MLPH in these cells led to a relatively modest, but statistically significant, increase in amiloridesensitive [Na.sup.+] current, suggesting the MLPH may be involved in ENaC trafficking. MyosinVc, the epithelial-specific class V myosin that is highly homologous to MyosinVa, another component of the melanosome trafficking complex, has putative consensus sites for serum and glucocorticoid-induced kinase 1 (SGK1), an early aldosterone-induced kinase that mediates some of aldosterone's effects on [Na.sup.+] transport. Our results indicate that MyosinVc is phosphorylated by endogenous SGK1, suggesting that this complex may be involved in the aldosterone-regulated trafficking of ENaC in the CCD. These results suggest potential mechanisms by which aldosterone may regulate [Na.sup.+] transport both directly, by increasing the abundance of MLPH, and indirectly by increasing the transcription of SGK1, which in turn regulates the activity of MyosinVc. epithelial [Na.sup.+] channel; myosin; serum and glucocorticoid-induced kinase

As a complex skeletal organ consisting of 2 functional and developmental units (ascending ramus and alveolar region), the mandible represents a well-established model in morphological integration studies. The concept of morphological integration assumes that developmentally or functionally related traits are more correlated than others and hence evolve together. We compared the level and pattern of mandibular morphological integration between groups of adult yellow-necked field mice (Apodemus flavicollis), with and without B chromosomes (Bs) in a population from Mr. Avala, Serbia. Bs are dispensable supernumerary chromosomes characterized by irregular and non-Mendelian modes of inheritance. The level of morphological integration was higher in animals with Bs. One of the 2 regions of the mandible tested (alveolar region) was significantly more affected by the presence of Bs than the other, with an increase in intensity of integration of 41.61% versus 15.86%. The hypothesis of morphological integration, which postulates disunion of the mandible into 2 distinct functional and developmental modules, was confirmed in animals with Bs. Bs probably have a function because they affect mandible phenotype (although the mechanism is unknown), increase variability within populations, and could lead to selective advantage. Key words: Apodemus flavicollis, B chromosomes, mandible, morphological integration

In 2004, we collected 211 specimens of European field mice (genus Apodemus; subgenus Sylvaemus) from 16 localities in northern, western, central, and southern Ukraine, including the Crimean Peninsula. We used cytochrome-b mitochondrial DNA sequence data to investigate species diversity, distributional patterns, and taxonomy of Apodemus in Ukraine. Sequence data proved useful for species-level discrimination, because the 11 species examined were defined by low levels of intraspecific variation (mean range, 0.00-3.35%) and by high levels of interspecific variation (mean range, 5.37-18.9%). We identified the 211 specimens to 1 of 4 species: A. flavicollis (n = 121), A. sylvaticus (n = 34), A. uralensis (n = 16), and A. witherbyi (n = 40). Although all 4 species are known from Ukraine, this study provides new information about the ranges and population identity for these species in southeastern Europe. For example, our analyses substantiate the marked genetic structure reported for A. sylvaticus and document the presence of northern and southern continental lineages of this species in Ukraine that are hypothesized to have been isolated from each other in glacial refugia approximately 1.5 million years ago (>5% genetic divergence). Banks of the Dneiper River in northern Ukraine represent an area of secondary contact for the 2 lineages. Additionally, although application of A. witherbyi as a species-level name is debatable, examination of our genetic and morphological data supports its validity and priority over junior synonyms A. hermonensis and A. iconicus. Key words: Apodemus, cytochrome b, distribution, Rodentia, Sylvaemus, systematics, taxonomy, Ukraine

The morphological identification of cryptic rodent species has historically been problematic. At best, many cryptic species have been identified by chromosomal differences. However, to study the life histories of such rodent species, there is a need for a molecular technique for cryptic species identification that does not involve destructive sampling. In this manuscript we examine mitochondrial DNA (mtDNA) cytochrome-b genetic variation in 2 cryptic murid rodent species, the red veld rat (Aethomys chrysophilus) and the Tete veld rat (A. ineptus) from southern Africa. Phylogenetic and phylogeographic analyses of these sequences showed reciprocal monophyly between populations of the 2 species in southern Africa, but no support for monophyly of A. chrysophilus from southern and eastern Africa. This suggests that the analysis of mtDNA can be used to distinguish these 2 sister species in southern Africa. However, these results need to be investigated further by DNA analyses of type specimens, topotypical material, or both from adjacent localities. Key words: Aethomys, cryptic species, molecular identification, phylogenetic analysis, southern Africa, systematics

A mouse model is used to delineate the underlying molecular mechanisms for urogenital development and heart morphogensis.

Mouse models were used to illustrate the role of the homeobox gene Lim1 in nephric duct development and ureteric bud outgrowth. It does so by maintaining and/or regulating nephric epithelium differentiation.

Mouse and Drosophila models are used to compare gene expression profiles regarding organ differentiation, including skin, liver, nervous system, and digestive system. Similar patterns emerge, indicating conservation of the temporal progression of gene expression processes; implications for future research are discussed.

The article compares and contrasts Nkx6 family genes in mice and chickens. Findings indicate genetic requirements for early foregut endoderm.

A comparison is presented between cow and mouse trophoblast differentiation programming, focusing on proliferation marker transcription and epiblast-specifying gene expression. Early elongation is found to be a crucial transition in bovine trophoblast differentiation.

Experiments were performed to examine the tissue distribution of three classes of high-affinity Na+-Pi cotransporters (Npts), the cellular receptors for murine gibbon ape leukemia virus (Glvr-1) and amphotropic murine retrovirus and quantitate their relative expression in the mouse kidney. Results show that while Npt2 was more abundant in the kidneys than in the intestine and not observed in the liver, while the Npt1 was seen in the liver and in smaller amounts in the kidney. On the other hand, Glvr-1 was observed to be expressed throughout the whole kidney.

Parapatric speciation across sharp ecological gradients is an alternative to the more usual allopatric model as both a general explanation of organismal diversification and as an explicit statement regarding differentiation of tropical forest biotas (Endler, 1977, 1982a, 1982b). The relevance of this model to species of small mammals distributed across a 3,000 meter gradient on the eastern flank of the Peruvian Andes is examined here by phylogenetic analysis of comparative mitochondrial DNA sequences, relying on both freshly collected samples and extracts taken from skins preserved in museum collections. These analyses falsify the applicability of the gradient model in this case. Moreover, the phylogenetic approach employed here provides an explicit test of the feasibility of the gradient model for any other taxon, either plant or animal, of the lowland Amazonian forest.

Geographic variation in the advertisement songs of sister species of neotropical singing mice, Scotinomys teguina and S. xerampelinus were quantified to evaluate the relative contributions of selection and drift to acoustic divergence in a mammal. Although much of the intraspecific acoustic variations were effectively neutral, selection was found to contribute significantly towards shaping species differences in song.

Imprinting effects were found for the traits spleen weight, liver weight, kidney weight, and abdominal fat percentage in mouse F(2) families.