Project description:Chitons are marine molluscs that posses a radula, a tongue like appendage containing many rows of microscopic teeth used for feeding. These teeth are hardened through the incorporation of biominerals. Since the original discovery of iron oxide and magnetite in these teeth, a wealth of chemical and structural knowledge has accumulated. The biomineralization process is known to be matrix mediated with precise control of the deposition of a number of different iron and calcium minerals at readily identifiable stages of tooth development. While much is known about the mechanisms of tooth mineralisation, there have been no studies undertaken to identify the genes that regulate this process. This investigation uses microarray technology to analyse the spatial expression of 493 expressed sequence tags (EST) derived from the radula sac of chiton, Acanthopleura hirtosa. A number of ESTs have been deemed significantly differentially expressed in relation to three designated areas of the radula sac. These spatial sections are defined by the variation in biomineral deposits of the radula, being immature radula which lacks any biomineral incorporation, iron deposition and calcium deposition. Additionally, foot muscle was used as a control to specify whether EST expression was specific to the radula and therefore likely involved biomineralization.
Project description:Chitons are marine molluscs that posses a radula, a tongue like appendage containing many rows of microscopic teeth used for feeding. These teeth are hardened through the incorporation of biominerals. Since the original discovery of iron oxide and magnetite in these teeth, a wealth of chemical and structural knowledge has accumulated. The biomineralization process is known to be matrix mediated with precise control of the deposition of a number of different iron and calcium minerals at readily identifiable stages of tooth development. While much is known about the mechanisms of tooth mineralisation, there have been no studies undertaken to identify the genes that regulate this process. This investigation uses microarray technology to analyse the spatial expression of 493 expressed sequence tags (EST) derived from the radula sac of chiton, Acanthopleura hirtosa. A number of ESTs have been deemed significantly differentially expressed in relation to three designated areas of the radula sac. These spatial sections are defined by the variation in biomineral deposits of the radula, being immature radula which lacks any biomineral incorporation, iron deposition and calcium deposition. Additionally, foot muscle was used as a control to specify whether EST expression was specific to the radula and therefore likely involved biomineralization. A total of twelve A. hirtosa specimens were collected and sacrificed for microarray hybridizations. The radulae were removed from each animal immediately following sacrifice and dissected into three sections based on the biomineralisation development of the radula teeth. These sections are termed immature teeth, iron deposited teeth, and calcium deposited teeth. An additional sample of A. hirtosa foot muscle was taken from each specimen. RNA was extracted individually from these sections. Extracted RNA samples across subjects were pooled equally within sections in order to minimize the impact of biological variation and maximize the number of individual samples included in the study. To this effect, four single channel hybridizations were conducted for each radula and muscle section each representing a pooled biological replicate containing equal proportions of RNA from three A. hirtosa individuals. A total of sixteen microarray hybridizations were conducted in this manner.
Project description:Molluscs biomineralize structures that vary in composition, form, and function, prompting questions about the genetic mechanisms responsible for their production and the evolution of these mechanisms. Chitons (Mollusca, Polyplacophora) are a promising system for studies of biomineralization because they build a range of calcified structures including shell plates and spine- or scale-like sclerites. Chitons also harden the calcified teeth of their rasp-like radula with a coat of iron (as magnetite). Here we present the genome of the West Indian fuzzy chiton Acanthopleura granulata, the first from any aculiferan mollusc. The A. granulata genome contains homologs of many genes associated with biomineralization in conchiferan molluscs. We expected chitons to lack genes previously identified from pathways conchiferans use to make biominerals like calcite and nacre because chitons do not use these materials in their shells. Surprisingly, the A. granulata genome has homologs of many of these genes, suggesting that the ancestral mollusc may have had a more diverse biomineralization toolkit than expected. The A. granulata genome has features that may be specialized for iron biomineralization, including a higher proportion of genes regulated directly by iron than other molluscs. A. granulata also produces two isoforms of soma-like ferritin: one is regulated by iron and similar in sequence to the soma-like ferritins of other molluscs, and the other is constitutively translated and is not found in other molluscs. The A. granulata genome is a resource for future studies of molluscan evolution and biomineralization.