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Comparative Study
, 6 (2), 67-77

Evolution of a Novel Function: Nutritive Milk in the Viviparous Cockroach, Diploptera Punctata

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Comparative Study

Evolution of a Novel Function: Nutritive Milk in the Viviparous Cockroach, Diploptera Punctata

Anna Williford et al. Evol Dev.

Abstract

Cockroach species show different degrees of maternal contribution to the developing offspring. In this study, we identify a multigene family that encodes water-soluble proteins that are a major component of nutritive "Milk" in the cockroach, Diploptera punctata. This gene family is associated with the evolution of a new trait, viviparity, in which the offspring receive nutrition during the gestation period. Twenty-five distinct Milk complementary DNAs were cloned and partially characterized. These complementary DNAs encode 22 distinct Milk peptides, each of length 171 amino acids, including a 16-amino acid signal peptide sequence. Southern blot analysis confirms the presence of multiple copies of Milk genes in D. punctata. Northern analysis indicates tissue- and stage-specific Milk gene expression. Examination of the deduced amino acid sequences identifies the presence of structurally conserved regions diagnostic of the lipocalin protein family. The shared exon/intron structure of one of the Milk loci with lipocalin genes further supports a close evolutionary relationship between these sequences.

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