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The study of gene function in testis and sperm has been greatly assisted by transgenic mouse models. Recently, an alternative way of expressing transgenes in mouse testis has been developed that uses electroporation to introduce transgenes into the male germ cells. This approach has been successfully used to transiently express reporter genes driven by constitutive and testis-specific promoters. It has been proposed as an alternative method for studying gene function in testis and sperm, and as a novel way to create transgenic animals. However, the low levels and transient nature of transgene expression that can be achieved using this technique have raised concerns about its practical usefulness. It has also not been demonstrated in mammals other than mice. In this study, we show for the first time that in vivo gene transfer using electroporation can be used to express a fluorescent transgene in the testis of a mammal other than mice, the Syrian golden hamster. Significantly, for the first time we demonstrate expression of a transgene in epididymal sperm using this approach. We show that expression of the transgene can be detected in sperm for as long as 60 days following gene transfer. Finally, we provide the first systematic demonstration that this technique does not lead to any significant long-term adverse effects on testicular integrity and sperm quality. This technique therefore offers a novel way to study gene function during fertilization in hamsters and may also have potential as a way of creating transgenic versions of this important model species.

Testicular development in the harbour porpoise Phocoena phocoena was examined using animals (n = 192) stranded or by-caught off the coast of England, Wales and Scotland. Classification of animals according to their stage of sexual development was undertaken using gonadal morphology and the distribution of cytoskeletal proteins. Smooth muscle actin (SMA) and vimentin proved particularly useful in this respect; SMA was prominent in the myoid peritubular cells of the adult testis, and two stages of peritubular cell SMA expression could be recognized ('absent' or 'incomplete'). The initial appearance of SMA in peritubular cells was associated with significant increases in body length and body weight (P < 0.001), and occurred during the second year of life. Vimentin, which was prominent in prespermatogonia and spermatogonia, sometimes showed a polarized cytoplasmic distribution. This correlated with a developmental stage at which the seminiferous tubule epithelium becomes populated by germ cells (mean age 1.8 years). Several antibodies were tested for their utility as Sertoli cell markers, but none was found to be specific or useful. Nevertheless, immunohistochemical localization of desmin, GATA-4, Ki67 and androgen receptor was possible despite the poor quality of tissue preservation. This study showed that immunohistochemical classification of these individuals provides a robust basis for the recognition of key physiological stages of sexual development in the male harbour porpoise. This may provide an alternative to the estimation of age, body weight and body length in future analyses aimed at detecting possible adverse effects of environmental pollutants on the reproductive potential of wild marine mammals.

The epithelium of the ductuli efferentes is composed of ciliated, principal, halo and basal cells. The supranuclear cytoplasm of ciliated cells is penetrated by particularly long cilial rootlets which are surrounded by numerous elongate mitochondria. Microtubules are arranged along the longitudinal axis of the cells. The spaces between the microvilli of principal cells form canaliculi which penetrate the apical cytoplasm and appear to be involved in endocytotic activity. The supranuclear cytoplasm contains oval mitochondria and numerous vacuoles. Both ciliated and principal cells contain poorly developed Golgi and endoplasmic reticulum, but numerous supranuclear dense bodies are usually present. Supranuclear and basal accumulations of dense bodies were identified as lipofuscin; they were the source of brown pigmentation in the proximal two thirds of the ductuli efferentes. The halo cells were probably macrophages. They occurred quite frequently and contained crescent shaped nuclei and large accumulations of lipofuscin material.

The pattern of normal spermatogenesis in the common marmoset, Callithrix jacchus, is described and a system classifying the spermatogenic cycle into nine successive stages is presented. In contrast to most previous studies of spermatogenesis, the classification system developed in this study depends more upon the recognition of characteristic cell associations rather than upon identification of particular steps of spermatid development. The structurally simple acrosome of the marmoset spermatozoon displays insufficiently clear morphological changes during spermatid elongation to allow this to be used as a key to spermatogenic classification. Ultrastructural aspects of spermatogenesis in the marmoset are also described; in general, these correspond to similar descriptions of this process in other primates.

Testicular development to 9 months of age has been studied. Seminiferous tubule diameter increased in a linear manner between 13 and 65 days of age, and there was a steep increase in testicular weight with age. At about 9 months the animals weighed 400-500 g and total testicular weight was about 10 g. This relatively large testicular size was correlated with high sperm density in the semen. Spermatogenesis commenced at about 21-25 days of age, when the first spermatids were found. Spermatozoa appeared in a small proportion of seminiferous tubules by 31-35 days of age, and were seen in the epididymides of an animal of 31 and another of 34 days. Epididymal spermatozoas were consistently present in large numbers after 60 days and this correlated with the increased frequency of mature seminiferous tubules. Leydig cell size increased rapidly from 13 to about 60 days, then remained constant. Inferences have been drawn from this and the study of spermatogenesis about the level of testosterone secretion. The results indicate that the male cuis is almost fully grown and sexually mature by about 90 days of age.