An electron microscope study of nebenkern formation and differentiation in spermatids of Murgantia histrionica (Hemiptera, Pentatomidae)

Abstract

Mitochondria in early spermatids of many insects aggregate and form a round body, the nebenkern. The nebenkern undergoes a structural differentiation and then divides into two separate equal-sized bodies. In the present study, nebenkerns of Murgantia histrionica, a Hemipteran insect, were reconstructed using electron micrographs of serial sections to determine how the mitochondria transform into the two separate bodies.Newly formed nebenkerns are made of one piece, an anastomosis of rod-like segments. Some segments interconnect to join networks of rings. Each network interlocks with another similar network, but networks which interlock are connected with each other by other segments of the nebenkern. Later, the entire nebenkern is made of two unconnected and interlocked networks of rings. The nebenkern appears to remain bipartite during subsequent differentiation. Since the two pieces are interlocked, breaks must occur before the pieces can separate. As breaks occur, each network transforms into a set of curved sheets, producing a nebenkern made of four concentric layers. The three outer layers are each made of two curved sheets which surround a bipartite central core. The surface sheets meet at a furrow in the surface of the nebenkern; segments in each layer are roughly symmetrical with each other about the plane in which the furrow lies. Rod-like segments join alternate segments. The number of layers then decreases to three, and later, to two. These nebenkerns resemble four-layered nebenkerns, but fewer connections between alternate segments are present. The two pieces constituting the nebenkern probably separate after most of the latter connections disappear. Hypotheses to account for the observed changes in nebenkern structure are presented.Studies with the light microscope have shown that mitochondria in early spermatids of many insects aggregate and form a round body, the nebenkern (Meves, '00; Gatenby, '17; Bowen, '22a; Pollister, ' 3 0 ) . In some Hemipterans, the mitochondria are long filaments before and during aggregation, but the newly formed nebenkern is dense and filaments can no longer be distinguished with the light microscope (Montgomery, '1 1 ; Bowen, '22a,b). Soon clear spaces appear within the nebenkern and the nebenkern resembles a collection of granular and rod-shaped mitochondria. Then the clear spaces seem to coalesce into several concentric layers (Bowen, '22b). Gradually the layers decrease in number and, as the last inner layer disappears, the nebenkern divides into two separate equalsized bodies.In single sections viewed with the electron microscope, newly formed nebenkerns appear to be aggregates of the separate mitochondria observed at telophase 11 (Tahmisian, et al., '56; deRobertis and Raffo, '57; Yasuzumi and Oura, '65). However, the observation that segments of nebenkerns made of concentric layers actually connect with each other to form two pieces was made in studies of short series of sections of nebenkerns in the butterfly Pieris (Andre, '59a, '62) and in the bug M...

Male reproductive system and spermatogenesis of Limodromus assimilis (Paykull 1790)

“…They aggregate and form the “nebenkern”, from which two mitochondrial derivates originate [42]. In several hymenopteran species, the two mitochondrial derivates can strongly differ in shape and size [1, 2, 22].…”

Power transmission along biological membranes

“…The formation of a mitochondrial reticulum during muscle ontogenesis may be compared to the phenomenon of the end-to-end aggregation of mitochondria accompanying the conversion of a spermatid to a spermatozoon (Pratt, 1968;Bacetti & Afzelius, 1976). Moreover, this type of aggregation was described as taking place in different tissues under the conditions of energy deficiency such as hypoxia, hyperthyroidism, hard work, etc.…”

Structural specialization in the flagellum of the spermatozoon of the bloodsucking bug (Rhodnius prolixus; Hemiptera, Reduviidae)

“…The spermatozoon head consists of an acrosome and nucleus, and the tail, of a long axoneme flanked by two mitochondrial derivative?.. It is well-known that the typical insect spermatid mitochondria undergoes complicated changes leading to the formation in the mature spermatozoon of the mitochondrial derivatives (Pratt, 1968;, which are located alongside the axoneme and which compose a larger part of the cell volume (Perotti, 1969). The presence of a prominent paracrystalline structure embedded in an amorphous matrix and precise organization of the cristae (Baccetti et al.…”