Biology subjects

Chipman, A. D.

Publications and source records attributed to Chipman, A. D..

3 recordsLinked to original sources

bioRxiv2018

Growth zone segmentation in the milkweed bug Oncopeltus fasciatus sheds light on the evolution of insect segmentation

One of the best studied developmental processes is the Drosophila segmentation cascade. However, this cascade is generally considered to be highly derived and unusual. We present a detailed analysis of the sequential segmentation cascade of the milkweed bug Oncopletus fasciatus, as a comparison to Drosophila, with the aim of reconstructing the evolution of insect segmentation. We analyzed the expression of 12 genes, representing different phases during segmentation. We reconstruct the spatio-temporal relationships among these genes And their roles and position in the cascade. We conclude that sequential segmentation in the Oncopeltus germband includes three phases: Primary pair-rule genes generate segmental gene expression in the anterior growth zone, followed by secondary pair-rule genes, expressed in the transition between the growth zone and the segmented germband. Segment polarity genes are expressed in the segmented germband. This process generates a single-segment periodicity, and does not have a double-segment pattern at any stage.

developmental biology↗

bioRxiv2018

Elongation during segmentation shows axial variability, low mitotic rates, and synchronized cell cycle domains in the crustacean, Thamnocephalus platyurus

Segmentation in arthropods typically occurs by sequential addition of segments from a posterior growth zone, but cell behaviors producing posterior elongation are not well known. Using precisely staged larvae of the crustacean, Thamnocephalus platyurus, we systematically examined cell division patterns and morphometric changes associated with posterior elongation during segmentation. We show that cell division is required for normal elongation but that cells in the growth zone need only divide ~1.5 times to meet that requirement; correspondingly, direct measures of cell division in the growth zone are low. Morphometric measurements of the growth zone and of newly formed segments suggest tagma-specific features of segment generation. Using methods for detecting two different phases in the cell cycle, we show distinct domains of synchronized cells in the posterior. Borders of cell cycle domains correlate with domains of segmental gene expression, suggesting an intimate link between segment generation and cell cycle regulation.\n\nSummary StatementPosterior growth zone has synchronized cell cycle domains but shows little cell division during segment addition in a crustacean. Dimensions of the shrinking posterior growth zone change at tagma boundaries.

developmental biology↗

bioRxiv2017

Molecular evolutionary trends and feeding ecology diversification in the Hemiptera, anchored by the milkweed bug genome

BackgroundThe Hemiptera (aphids, cicadas, and true bugs) are a key insect order, with high diversity for feeding ecology and excellent experimental tractability for molecular genetics. Building upon recent sequencing of hemipteran pests such as phloem-feeding aphids and blood-feeding bed bugs, we present the genome sequence and comparative analyses centered on the milkweed bug Oncopeltus fasciatus, a seed feeder of the family Lygaeidae.\n\nResultsThe 926-Mb Oncopeltus genome is well represented by the current assembly and official gene set. We use our genomic and RNA-seq data not only to characterize the protein-coding gene repertoire and perform isoform-specific RNAi, but also to elucidate patterns of molecular evolution and physiology. We find ongoing, lineage-specific expansion and diversification of repressive C2H2 zinc finger proteins. The discovery of intron gain and turnover specific to the Hemiptera also prompted evaluation of lineage and genome size as predictors of gene structure evolution. Furthermore, we identify enzymatic gains and losses that correlate with feeding biology, particularly for reductions associated with derived, fluid-nutrition feeding.\n\nConclusionsWith the milkweed bug, we now have a critical mass of sequenced species for a hemimetabolous insect order and close outgroup to the Holometabola, substantially improving the diversity of insect genomics. We thereby define commonalities among the Hemiptera and delve into how hemipteran genomes reflect distinct feeding ecologies. Given Oncopeltus's strength as an experimental model, these new sequence resources bolster the foundation for molecular research and highlight technical considerations for the analysis of medium-sized invertebrate genomes.

genomics↗