Atomic force microscopy of mammalian sperm chromatin.

We have used the atomic force microscope (AFM) to image the surfaces of intact bull, mouse and rat sperm chromatin and partially decondensed mouse sperm chromatin attached to coverglass. High resolution AFM imaging was performed in air and saline using uncoated, unfixed and unstained chromatin. Images of the surfaces of intact chromatin from all three species and of an AFM-dissected bull sperm nucleus have revealed that the DNA is organized into large nodular subunits, which vary in diameter between 50 and 100 nm. Other images of partially decondensed mouse sperm chromatin show that the nodules are arranged along thick fibers that loop out away from the nucleus upon decondensation. These fibers appear to stretch or unravel, generating narrow smooth fibers with thicknesses equivalent to a single DNA-protamine complex. High resolution AFM images of the nodular subunits suggest that they are discrete, ellipsoid-shaped DNA packaging units possibly only one level of packaging above the protamine-DNA complex.

Morphometric analysis of intact sperm heads and of sperm nuclei in the mouse.

A morphometric analysis of mouse sperm and of their nuclei was undertaken to investigate their respective post-testicular maturation. Sperm were collected from the testis, caput and cauda epididymidis, and their corresponding nuclei were isolated. Results indicate that the post-testicular maturation of sperm is distinct from that of nuclei. The size of intact sperm heads increases in the caput followed by a subsequent decrease in the cauda. In contrast, sperm nuclei decrease progressively in size. In general, a greater magnitude and number of alterations in intact heads and nuclei occur while in transit from the testis to the caput than during passage to the cauda epididymis. These results suggest that the period immediately following their release from the testis is crucial to the complete morphological maturation of sperm heads and nuclei.

Quantitative fluorometry of abnormal mouse sperm nuclei.

An extensive quantitative analysis of deformed mouse spermatozoa was undertaken. Improvements over previous studies included the isolation and purification of sperm nuclei, a multifaceted analytical approach using several fluorochromes and the analysis of individual nuclei classified into shape categories. Malformed sperm nuclei in BALB/c mice could not be distinguished from normal ones in terms of total and basic proteins, sulfhydryl and disulfide group concentration, DNA concentration and chromatin organization. The shape of sperm nuclei is therefore probably determined by the manner in which the internal biochemical components are assembled.

A QuickBasic computer model of spermatogenesis.

A program in QuickBasic has been written for the purpose of simulating spermatogenesis in any animal in order to more fully understand the dynamics of sperm production. Two basic informations are needed to run the program: controlling factors (CF-s) and the stem cell population size. These can be interactively manipulated for theoretical evaluations or be implemented from actual animal data for assessment of valid sperm yield.

Effects of X-irradiation on the kinetics of abnormal sperm production and sperm loss in the mouse.

Exposure of male mice to 6 Gy of X-rays resulted in a very rapid and extensive sloughing of the germinal epithelium as shown by the accumulation of non-sperm cells within the lumen of the epididymis. These cells were identified as stage 1 and 2 round spermatids. After accumulating in the caput, they progressed through the epididymis over the weeks of sampling and, by Week 9 after irradiation, they had completely disappeared from the organ. It is suggested that the precocious loss of round spermatids is responsible for the induction of oligospermy within the testis and the caput epididymidis. Similar sperm losses from the cauda epididymidis were not observed. Radiation also enhanced the frequency of misshapen spermatozoa normally found in this strain. From kinetic considerations, it is suggested that the generation of abnormal spermatozoa may be biphasic with an early component comprising maturing spermatids and a late contingent composed of affected spermatocytes. Return to the pre-irradiation level of abnormal frequency was not observed within the time frame of this study (10 weeks), perhaps indicating residual damage. The synchrony that existed among the various organs in terms of both sperm loss and the generation of abnormal spermatozoa may be the result of a rapid dispersion of gametes from the testis and not due to local responses as would be expected if sperm flow were affected by the irradiation. The distribution of abnormal sperm types was different in the testis from that in the epididymis, presumably because of a testicular spermatophagic mechanism specific for the removal of certain deformities. It is concluded that the kinetics of spermatogenesis, of spermiogenesis, and of sperm transport in the mouse is not affected by exposure to 6 Gy of X-rays.