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Introduction: Diseases and lesions of the skin in crocodilians, especially in farmed animals, result in heavy economic losses. Differentiation and regeneration of skin depends on epidermal and dermal cellular mitotic proliferation. Thus, a quick and reliable overview of mitotic cells is important when examining crocodile tissue samples. The objective of this study was to establish a marker for cell proliferation in the crocodile. Material and Methods: Samples from Estuarine crocodiles, taken following appropriate intravenous barbiturate euthanasia under scientiﬁc licence (Parks and Wildlife Commission of the Northern Territory (Australia), Permit 3640), were obtained at different developmental stages, starting from day 14 in ovo, and including juvenile, and adult animals. Skin samples were taken from the head, neck, belly, dorsal trunk, and tail. In addition, samples from most organs and tissues were taken. Immunohistochemistry was carried out on parafﬁn embedded sections using an antibody to Proliferating Cell Nuclear Antigen (Mouse-anti-PCNA; Dako); counterstaining was done with fast red.
Results: PCNA was established successfully as a mitotic marker in the crocodile. Positive staining for PCNA was detected in all specimens. Belly and dorsal skin of adult animals showed different thickness of epidermal layers (s- tratum basale, intermedium and corneum). Staining was very distinct in the basal layers and in the deeper part of
the stratum intermedium. Likewise, positive cells were found in the tongue, liver, bone marrow, and somites.
Conclusion: This study showed for the ﬁrst time that PCNA, which is a highly conserved nuclear protein (“archaeoprotein”) that serves as an auxiliary protein of DNA polymerase and functions during DNA replication (Chapman et al. Int J Dev Biol 1994; 38 491–497), can be used as a mitotic marker in the crocodile.