Background:In angiosperms, the endosperm plays a crucial placenta-like role in that not only is it necessary for nurturing the embryo, but also regulating embryogenesis through complicated genetic and epigenetic interactions with other seed compartments and is the primary tissue in which genomic imprinting occurs.Results:We observed a gradual increase of paternal siRNA expression in the early stages of kernels and an expected 2:1 maternal to paternal ratio in 7-DAP endosperm via sequencing of small interfering RNA (siRNA) transcriptomes in developing kernels (0, 3 and 5 days after pollination (DAP)) and endosperms (7, 10 and 15 DAP) from the maize B73 and Mo17 reciprocal crosses. Additionally, 460 imprinted siRNA loci were identified in the endosperm, with the majority (456/460, 99.1%) being maternally expressed at 10 DAP. Moreover, 13 out of 29 imprinted genes harbored imprinted siRNA loci within their 2-kb flanking regions, a significant higher frequency than expected based on simulation analysis. Additionally, gene ontology terms of "response to auxin stimulus", "response to brassinosteroid stimulus" and "regulation of gene expression" were enriched with genes harboring 10-DAP specific siRNAs, whereas those of "nutrient reservoir activity", "protein localization to vacuole" and "secondary metabolite biosynthetic process" were enriched with genes harboring 15-DAP specific siRNAs.Conclusions:A subset of siRNAs subjected to imprinted expression pattern in maize developing endosperm, and they are likely correlated with certain imprinted gene expression. Additionally, siRNAs might influence nutrient uptake and allocation processes during maize endosperm development.

No description available.

Genomic imprinting provides an exception to the Mendelian rule of inheritance, as imprinted genes are preferentially expressed in a parent-of-origin specific manner. They play important roles in the development of embryonic and extra-embryonic lineages and postnatally in the maintenance of correct metabolic homeostasis as well as regulation of adult behaviour. The parental conflict theory predicts that maternally expressed genes act as growth suppressors, limiting the usage of maternal resources, and that paternally expressed genes function in an opposite manner to promote growth at the expense of maternal resources. Growth factor bound protein 10 (Grb10) is an imprinted gene encoding an intracellular adaptor protein that can interact with several receptor tyrosine kinases and downstream signalling molecules. Recently, our lab has identified Grb10 as a unique imprinted gene capable of influencing fetal growth, postnatal energy metabolism and adult behaviour depending on functions of each of the parental alleles in distinct tissues. Grb10 predominantly expressed from the maternal allele during embryogenesis affects fetal and placental growth along with postnatal glucose homeostasis, whereas paternal Grb10 expression within the CNS influences social behaviour. Delta-like homologue 1 is (Dlk1) a paternally expressed imprinted gene coding for a protein belonging to the Notch/Delta family that acts as a membrane-associated or a soluble protein known to regulate differentiation of various cell types, notably adipocytes. In vivo Dlk1 has been associated with perinatal survival, regulation of normal growth and development and maintenance of the correct course of adipogenesis. Here a hypothesis is proposed that Grb10, as a predominantly maternally expressed growth inhibitor and Dlk1, a paternally expressed growth promoter, act antagonistically in a common genetic pathway. To test this hypothesis, we have generated Grb10m/+/Dlk1+/p double knockout mice and performed a phenotypic characterisation in comparison with wild type as well as the respective single knockout animals. Results obtained from allometric and metabolic analyses, together with histological studies, reveal strong similarities between the phenotypes of Grb10m/+and Grb10m/+/Dlk1+/p knockout mice. We found that overgrowth of Grb10m/+/Dlk1+/p embryos and placentae resemble the phenotype seen in Grb10m/+ mutants and that tissue overgrowth most likely results from higher proliferation rates of Grb10m/+and Grb10m/+/Dlk1+/p cells. Furthermore, Grb10m/+and Grb10m/+/Dlk1+/p knockout mice each exhibit improved glucose clearance and share an unusual characteristic accumulation of lipid in neonatal liver. These results are consistent with the proposed hypothesis and indicate that the Dlk1 and Grb10 genes might be involved in the same genetic pathway. Moreover, the data suggest Dlk1 is an inhibitor of Grb10 which is in turn acting as a growth suppressor.

A gene is imprinted when its expression is dependent on the sex of the parent from which it was inherited. An increasing number of studies are suggesting that imprinted genes have a major influence on medically, agriculturally and evolutionarily important traits, such as disease severity and livestock production traits. While some genes have a large effect on the traits of an individual, quantitative characters such as height are influenced by many genes and by the environment, including maternal effects. The interaction between these genes and the environment produces variation in the characteristics of individuals. Many quantitative characters are likely to be influenced by a small number of imprinted genes, but at present there is no general theoretical model of the quantitative genetics of imprinting incorporating multiple loci, environmental effects and maternal effects. This research develops models for the quantitative genetics of imprinting incorporating these effects, including deriving expressions for genetic variation and resemblances between relatives. Imprinting introduces both parent-of-origin and generation dependent differences in the derivation of standard quantitative genetic models that are generally equivalent under Mendelian expression. Further, factors such as epistasis, maternal effects and interactions between genotype and environment may mask the effect of imprinting in a quantitative trait. Maternal effects may also mimic a number of signatures in variance and covariance components that are expected in a population with genomic imprinting. This research allows a more comprehensive understanding of the processes influencing an individual�s characteristics.

No description available.

The purpose of the current set of experiments was to investigate the interaction component of avian attachment behaviour. The latter is viewed as the outcome of several components, all of which potentially interact with each other. In these experiments, the visual, brood size, animate vs. inanimate, and familiarity components of avian attachment behaviour were held constant so that the effects of interaction were evaluated unambiguously. The results for Time 1 (T1) yielded various results for both Condition A (Interaction with the other species/breed) and B (Interaction with same species/breed). For T2 (Condition A), the four Experiments yielded various results. For T2 (Condition B), the four Experiments yielded consistent results. When experimental subjects interacted with their own species/breed (white Peking duckling), the preference for their own species/breed (white Peking ducklings) increased while the preference for the other species/breed (domestic chicks or mallard ducklings) decreased. In Experiment 3 and Experiment 4, there was a complete reversal of preference from T1 to T2.

“The scientist, by the very nature of his commitment, creates more and more questions, never fewer. Indeed the measure of our intellectual maturity, one philosopher suggests, is our capacity to feel less and less satisfied with our answers to better problems.” ~G.W. Allport, Becoming, 1955 It will be interesting to look back at this thesis in a few decades and reflect on how the questions and interpretation of data in the field of developmental biology have changed. Indeed, a biologist currently in their twilight years might reflect on their youth, before the discovery of hereditary material, and compare that bookend with the range of genome sequences and related knowledge currently available. How long will it take before this thesis reads like a debate about whether the male or female contributed the ‘homunculus,’ a miniature preformed human to the embryo that grows into an adult? In this thesis I asked three related questions: whether the role of Oct4 during embryogenesis provides insight into its contribution to pluripotency; how surfaceome changes contribute to functional maturation of neural stem cells and to what extent the murine genome is imprinted. Our data indicate that Oct4 is required for posterior expansion. We propose that the function of the protein is conserved, but that its expression has been coopted to yield different cell types based on its combination with different factors. We show that fundamental aspects of cell biology are altered during the maturation from pluripotent populations to neural stem cells, and identify mediators of proliferation, survival and adhesion that distinguish neural stem cell regulation from their precursors. Finally, we validated discovery of a dozen novel imprinted transcripts using a genomic approach. These discoveries will contribute to a holistic view of the causes and consequences of imprinting, but do not support a paradigm shift in the scale and consequences of imprinting.

“The scientist, by the very nature of his commitment, creates more and more questions, never fewer. Indeed the measure of our intellectual maturity, one philosopher suggests, is our capacity to feel less and less satisfied with our answers to better problems.” ~G.W. Allport, Becoming, 1955 It will be interesting to look back at this thesis in a few decades and reflect on how the questions and interpretation of data in the field of developmental biology have changed. Indeed, a biologist currently in their twilight years might reflect on their youth, before the discovery of hereditary material, and compare that bookend with the range of genome sequences and related knowledge currently available. How long will it take before this thesis reads like a debate about whether the male or female contributed the ‘homunculus,’ a miniature preformed human to the embryo that grows into an adult? In this thesis I asked three related questions: whether the role of Oct4 during embryogenesis provides insight into its contribution to pluripotency; how surfaceome changes contribute to functional maturation of neural stem cells and to what extent the murine genome is imprinted. Our data indicate that Oct4 is required for posterior expansion. We propose that the function of the protein is conserved, but that its expression has been coopted to yield different cell types based on its combination with different factors. We show that fundamental aspects of cell biology are altered during the maturation from pluripotent populations to neural stem cells, and identify mediators of proliferation, survival and adhesion that distinguish neural stem cell regulation from their precursors. Finally, we validated discovery of a dozen novel imprinted transcripts using a genomic approach. These discoveries will contribute to a holistic view of the causes and consequences of imprinting, but do not support a paradigm shift in the scale and consequences of imprinting.

The purpose of the current set of experiments was to investigate the interaction component of avian attachment behaviour. The latter is viewed as the outcome of several components, all of which potentially interact with each other. In these experiments, the visual, brood size, animate vs. inanimate, and familiarity components of avian attachment behaviour were held constant so that the effects of interaction were evaluated unambiguously. The results for Time 1 (T1) yielded various results for both Condition A (Interaction with the other species/breed) and B (Interaction with same species/breed). For T2 (Condition A), the four Experiments yielded various results. For T2 (Condition B), the four Experiments yielded consistent results. When experimental subjects interacted with their own species/breed (white Peking duckling), the preference for their own species/breed (white Peking ducklings) increased while the preference for the other species/breed (domestic chicks or mallard ducklings) decreased. In Experiment 3 and Experiment 4, there was a complete reversal of preference from T1 to T2.

A gene is imprinted when its expression is dependent on the sex of the parent from which it was inherited. An increasing number of studies are suggesting that imprinted genes have a major influence on medically, agriculturally and evolutionarily important traits, such as disease severity and livestock production traits. While some genes have a large effect on the traits of an individual, quantitative characters such as height are influenced by many genes and by the environment, including maternal effects. The interaction between these genes and the environment produces variation in the characteristics of individuals. Many quantitative characters are likely to be influenced by a small number of imprinted genes, but at present there is no general theoretical model of the quantitative genetics of imprinting incorporating multiple loci, environmental effects and maternal effects. This research develops models for the quantitative genetics of imprinting incorporating these effects, including deriving expressions for genetic variation and resemblances between relatives. Imprinting introduces both parent-of-origin and generation dependent differences in the derivation of standard quantitative genetic models that are generally equivalent under Mendelian expression. Further, factors such as epistasis, maternal effects and interactions between genotype and environment may mask the effect of imprinting in a quantitative trait. Maternal effects may also mimic a number of signatures in variance and covariance components that are expected in a population with genomic imprinting. This research allows a more comprehensive understanding of the processes influencing an individual�s characteristics.