Cellular and ultrastructural characterization of the grey-morph phenotype in southern right whales (Eubalaena australis)

Southern right whales (SRWs, Eubalena australis) are polymorphic for an X-linked pigmentation pattern known as grey morphism. Most SRWs have completely black skin with white patches on their bellies and occasionally on their backs; these patches remain white as the whale ages. Grey morphs (previously referred to as partial albinos) appear mostly white at birth, with a splattering of rounded black marks; but as the whales age, the white skin gradually changes to a brownish grey color. The cellular and developmental bases of grey morphism are not understood. Here we describe cellular and ultrastructural features of grey-morph skin in relation to that of normal, wild-type skin. Melanocytes were identified histologically and counted, and melanosomes were measured using transmission electron microscopy. Grey-morph skin had fewer melanocytes when compared to wild-type skin, suggesting reduced melanocyte survival, migration, or proliferation in these whales. Grey-morph melanocytes had smaller melanosomes relative to wild-type skin, normal transport of melanosomes to surrounding keratinocytes, and normal localization of melanin granules above the keratinocyte nuclei. These findings indicate that SRW grey-morph pigmentation patterns are caused by reduced numbers of melanocytes in the skin, as well as by reduced amounts of melanin production and/or reduced sizes of mature melanosomes. Grey morphism is distinct from piebaldism and albinism found in other species, which are genetic pigmentation conditions resulting from the local absence of melanocytes, or the inability to synthesize melanin, respectively.This is an open access article, free of all copyright, and may be freely reproduced, distributed, transmitted, modified, built upon, or otherwise used by anyone for any lawful purpose. The work is made available under the Creative Commons CC0 public domain dedication.Fil: Eroh, Guy D.. Huntsman Cancer Institute; Estados Unidos. University of Georgia; Estados UnidosFil: Clayton, Fred C.. University of Utah; Estados UnidosFil: Florell, Scott R.. University of Utah; Estados UnidosFil: Cassidy, Pamela B.. Huntsman Cancer Institute; Estados Unidos. Oregon Health & Science University; Estados UnidosFil: Chirife, Andrea. Instituto de Conservación de Ballenas. Programa de Monitoreo Sanitario de la Ballena Franca Austral; ArgentinaFil: Marón, Carina Flavia. University of Utah; Estados Unidos. Instituto de Conservación de Ballenas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Valenzuela, Luciano Oscar. University of Utah; Estados Unidos. Universidad Nacional del Centro de la Provincia de Buenos Aires. Facultad de Ciencias Sociales; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; ArgentinaFil: Campbell, Michael S.. University of Utah; Estados Unidos. Cold Spring Harbor Laboratory; Estados UnidosFil: Seger, Jon. University of Utah; Estados UnidosFil: Rowntree, Victoria J.. University of Utah; Estados Unidos. Instituto de Conservación de Ballenas. Programa de Monitoreo Sanitario de la Ballena Franca Austral; Argentina. Ocean Alliance; Estados UnidosFil: Leachman, Sancy A.. Oregon Health & Science University; Estados Unidos. Huntsman Cancer Institute; Estados Unido