Helical inclusions and atypical cristae in the mitochondria of the rabbit thyroid gland

Abstract

Paracrystalline arrays of the helical type were found in the mitochondria of the follicular cell of the rabbit thyroid gland. The mitochondria with the inclusions were enlarged and located close to the nucleus and in relation to the endoplasmic reticulum. The formation of the atypical cristae preceded the formation of the helical structures. Two major forms were present, depending on the plane of section of the inclusion. Longitudinal sections revealed a tight junction configuration and the obliquely sectioned inclusions presented oblique parallel arrays suggesting the filamentous nature of the inclusion. They were about 300 Å in width and spaced about 400 Å apart. The parallel arrays were obliquely directed with an angle of 45° to the vertical axis of the inclusion, the fibers were 70 Å in width and had a pitch of 250 Å. These inclusions were not related to colloid or lysosomes. However, their location suggests they could play a role in protein synthesis and may also be related to DNA. Further studies have to be conducted to elucidate the exact role of these inclusions.