Mitochondrial cristae diversity in human Leydig cells: a revised look at cristae morphology in these steroid-producing cells.

Mitochondria of steroid-producing cells are integrally involved with steroidogenesis. For decades, the mitochondrial morphology of Leydig cells, as with other steroid-producing cells, has been known to differ from typical mitochondria in that the cristae are predominately "tubular." In a few species, humans being one example, the cristae have often been further categorized as "tubular and/or lamellar," without further elaboration. In the present study, mitochondria of human Leydig cells were examined with the purpose of providing a more detailed description of "cristae" morphology in these steroid-producing cells. The cristae are found to be rather diverse in morphology, consisting of elements of anastomosing tubules in continuity with small cisternal regions as well as with stacked arrays of lamellae, referred to as "lamellar associations." The tubular elements are found to branch in a tripartite fashion and sometimes to expand into small cisternal elements at these junctures. The lamellar associations are a distinctive feature of cristae in human Leydig cells and consist of two to eight closely apposed lamellae with a consistent gap of approximately 4 nm between the membranes of apposing lamellae. Such a close association of cellular membranes is highly suggestive of an integral transmembrane linkage. Although the lamellar associations often appear isolated, evidence is present of a continuity of this compartment of the cristae with the tubular elements. The connections (termed "initial segments") of the various forms of the cristae to the inner mitochondrial membrane are typically via tubules. Mitochondria exhibiting a central region of matrix delineated by one or more cup-shaped lamellae are also present. The pleomorphic structure of mitochondrial cristae in human Leydig cells reemphasizes our present lack of knowledge of how subcellular structure relates to steroidogenesis.