Expression of anterior <i>Hox</i> genes during larval development of the gastropod <i>Haliotis asinina</i>

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<jats:p><jats:bold>Summary </jats:bold> We report the spatial expression patterns of five anterior <jats:italic>Hox</jats:italic> genes during larval development of the gastropod mollusc <jats:italic>Haliotis asinina</jats:italic>, an unsegmented spiralian lophotrochozoan. Molecular alignments and phylogenetic analysis indicate that these genes are homologues of <jats:italic>Drosophila</jats:italic> HOM‐C genes <jats:italic>labial</jats:italic>, <jats:italic>proboscipedia</jats:italic>, <jats:italic>zen</jats:italic>, <jats:italic>Deformed</jats:italic>, and <jats:italic>Sex combs reduced</jats:italic>; the abalone genes are named <jats:italic>Has‐Hox1</jats:italic>, <jats:italic>‐Hox2</jats:italic>, <jats:italic>‐Hox3</jats:italic>, <jats:italic>‐Hox4</jats:italic>, and <jats:italic>‐Hox5</jats:italic>. <jats:italic>Has‐Hox</jats:italic> transcripts are first detected in the free‐swimming trochophore larval stage and restricted to the posttrochal ectoderm. <jats:italic>Has‐Hox2</jats:italic>, <jats:italic>‐Hox3</jats:italic>, and <jats:italic>‐Hox4</jats:italic> are expressed in bilaterally symmetrical and overlapping patterns in presumptive neuroectodermal cells on the ventral side of the trochophore. <jats:italic>Has‐Hox1</jats:italic> expression is restricted to a ring of cells on the dorsoposterior surface, corresponding to the outer mantle edge where new larval shell is being synthesized. There appears to be little change in the expression domains of these <jats:italic>Has‐Hox</jats:italic> genes in pre‐ and posttorsional veliger larvae, with expression maintained in ectodermal and neuroectodermal tissues. <jats:italic>Has‐Hox2</jats:italic>, <jats:italic>‐Hox3</jats:italic>, <jats:italic>‐Hox4</jats:italic>, and<jats:italic>‐Hox5</jats:italic> appear to be expressed in a colinear manner in the ganglia and connectives in the twisted nervous system. This pattern is not evident in older larvae. <jats:italic>Has‐Hox1</jats:italic> and<jats:italic>‐Hox4</jats:italic> are expressed in the margin of the mantle in the posttorsional veliger, suggesting that <jats:italic>Hox</jats:italic> genes play a role in gastropod shell formation.</jats:p>

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