Journal of experimental zoology. Part B, Molecular and developmental evolution最新文献

Shells, spicules, and chaetae are diverse among extant and extinct spiralians such as mollusks, annelids, or brachiopods. These hard parts serve different functions, but their formation process and evolutionary interrelationships are still contentious. We investigated the expression of evolutionarily conserved transcription factor encoding genes as well as the structural genes chitin synthase and ferritin in cells giving rise to shells and spicules of aculiferans, i.e. the polyplacophoran Acanthochitona fascicularis and the neomeniomorph Wirenia argentea, as well as the conchiferan cephalopod Xipholeptos notoides and the scaphopod Antalis entalis. Polyplacophorans and neomeniomorphs express hox1 (only neomeniomorphs), goosecoid, grainyhead, and chitin-synthase in their spicules. Grainyhead, notch, delta, and zic are expressed in the polyplacophoran shell fields and spicule-bearing cells. In conchiferans, hox1 (scaphopods and cephalopods), goosecoid, and grainyhead (scaphopods) are expressed in the shell fields. Ferritin, is a gene that has been shown to be expressed in the gastropod shell field; however, it is not expressed in the shell fields or by the spicule-bearing cells of the studied species. Our study shows that all candidate genes are expressed in epithelia that give rise to spicules and shells, revealing a close relationship between spicule-bearing cells and shell fields. In contrast, ferritin expression in the shell field appears to be a gastropod innovation. Building on previous research involving brachiopod and annelid chaetal sacs, our results suggest that spicules may have predated molluscan shells and may be homologous to brachiopod and annelid chaetae. If this were true, then conchiferan mollusks would have secondarily lost spicules.

From the very moment of fertilization and throughout development, the cells of animal embryos have to continuously orchestrate the dynamic reorganization of their epigenetic landscapes. One of the earliest major events of this reorganization occurs during the time of the maternal-zygotic transition (MZT), when the control of the developmental process gradually shifts from maternal factors (initially present within the oocytes) to the genes of the embryo itself. As maternal transcripts and proteins are degraded, parental epigenetic information is often erased, and pioneer factors will turn on the transcriptional activity of the zygotic genome. This activation also coincides with the decompaction of the chromatin, which is essential for the successful initiation of gene expression in the zygote. Interestingly, in the past decades numerous studies reported findings that supported the role of noncanonical nucleotides in the process of MZT. These nucleobase moieties in these noncanonical nucleotides are covalently modified versions of the canonical bases, and often show a very dynamic presence within the genome. While most of the recent studies have deciphered in great detail the epigenetic role of methylcytosine and its derivates, other Noncanonical bases have received less attention. Here we suggest that the incorporation of nucleotides from deoxyuridine-triphosphate (dUTP) or 6-methyl-deoxyadenine-triphosphate (6m-dATP) into the genome is not mere noise or replication error but serves a well-defined purpose: to aid chromatin decompaction through the timely induction of DNA repair pathways.

Cave-dwelling animals thrive in isolated caves despite the pressures of darkness, starvation, and reduced oxygen. Prior work revealed that Astyanax cave-dwelling morphs derived from different cave localities express significantly higher levels of blood hemoglobin compared to surface-dwelling fish. Interestingly, this elevation is maintained in different populations of cavefish, despite captive rearing in normal oxygen conditions. We capitalized on the consistent response of elevated hemoglobin in captive cavefish, which were derived from geographically distinct regions, to determine if this elevation is underpinned by expression of the same Hb genes. Blood hemoglobin proteins are encoded by a large family of hemoglobin (Hb) gene family members, which demonstrate coordinated expression patterns, subject to various organismal (e.g., period of life history) and environmental influences (e.g., oxygen availability). Surprisingly, we found that geographically distinct populations showed mostly divergent patterns of Hb gene expression. Cavefish from two cave localities, Pachón and Tinaja, have a more recent shared origin, and show more similar Hb expression patterns as adults. However, during embryonic phases, Pachón and Tinaja show significant variability in timing of peak expression of Hb family members. In sum, the transcriptomic underpinnings of Hb gene expression represents a complex composite of shared and divergent expression patterns across three captive cavefish populations. We conclude that these differential patterns are likely influenced by life history, and the unique cave conditions in which these animals evolved.

Developmental plasticity, the ability of a genotype to produce different phenotypes in response to environmental conditions, has been subject to intense studies in the last four decades. The self-fertilising nematode Pristionchus pacificus has been developed as a genetic model system for studying developmental plasticity due to its mouth-form polyphenism that results in alternative feeding strategies with a facultative predatory and non-predatory mouth form. Many studies linked molecular aspects of the regulation of mouth-form polyphenism with investigations of its evolutionary and ecological significance. Also, several environmental factors influencing P. pacificus feeding structure expression were identified including temperature, culture condition and population density. However, the nutritional plasticity of the mouth form has never been properly investigated although polyphenisms are known to be influenced by changes in nutritional conditions. For instance, studies in eusocial insects and scarab beetles have provided significant mechanistic insights into the nutritional regulation of polyphenisms but also other forms of plasticity. Here, we study the influence of nutrition on mouth-form polyphenism in P. pacificus through experiments with monosaccharide and fatty acid supplementation. We show that in particular glucose supplementation renders worms non-predatory. Subsequent transcriptomic and mutant analyses indicate that de novo fatty acid synthesis and peroxisomal beta-oxidation pathways play an important role in the mediation of this plastic response. Finally, the analysis of fitness consequences through fecundity counts suggests that non-predatory animals have an advantage over predatory animals grown in the glucose-supplemented condition.