The koala (Phascolarctos cinereus) prostate: a comprehensive histological and immunohistochemical investigation

Abstract

The prostate of the koala (Phascolarctos cinereus), and of marsupials more generally, is the primary contributor of seminal fluid, but comparatively little is known about its microanatomy and/or biochemistry. This study explored evidence of parenchymal segmentation of the koala prostate. The prostate of three sexually mature koalas, euthanised for welfare reasons, were processed for histopathology, histochemistry (Masson’s trichrome, Alcian Blue, PAS staining) and immunohistochemistry (IHC) using basal (p63, CK14) and luminal (CK8/18, PSA, AR) markers. Results confirmed clear tissue segmentation of the koala prostate into three zones, anterior, central and posterior, characterised by differences in the proportion of glandular tissue, as well as the thickness of collagen fibres; there were also distinct differences in the morphology of secretions produced in each zone. Based on immunohistochemistry, the koala prostate showed evidence of both basal proliferative and luminal secretory cells. The ratio of basal to luminal cells varied across the three segments, with the central segment housing the highest density of basal cells. Globular bodies produced in the anterior zone were shown to possess the same markers as those that have been described for human prostasomes. This study appears to be the first to comprehensively document the marsupial prostate in terms of microanatomy and corresponding immunohistochemistry. While further biochemical analysis, such as proteomics of each segment will better define the relative functions of each tissue, the data presented here is consistent with the hypothesis that the koala prostate potentially represents an example of an ontological stage in the evolutionary differentiation of male eutherian accessory glands.