Comparative Testis Morphometry and Seminiferous Epithelium Cycle Length in Donkeys and Mules1

Abstract

The mule (Equus mulus mulus) is a sterile hybrid domestic animal that results from the breeding of a male donkey (Equus asinus) to a female horse (Equus caballus). Usually, spermatogenesis in mules does not advance beyond spermatocytes. In the present study, we performed a comparative and more accurate morphometric and functional investigation of the testis in donkeys and mules. Due to the smaller testis size, lower seminiferous tubule volume density, and fewer germ cells, the total length of seminiferous tubules in mules was significantly smaller than in donkeys. However, the percentage of seminiferous tubules containing germ cells (spermatogonia and spermatocytes) in mules was approximately 95%. The total number of Sertoli cells per testis observed in donkeys and mules was very similar. However, the total number of Leydig cells in mules was approximately 70% lower than in donkeys. At least in part, this difference was probably related to the lower number of germ cells present in mule seminiferous tubules. Although spermatogenesis in mules did not advance beyond secondary spermatocytes/newly formed round spermatids, germ cell associations in the seminiferous epithelium and pachytene spermatocytes nuclear volume in donkeys and mules were similar. The duration of spermatogenesis was estimated using intratesticular injections of tritiated thymidine. Each spermatogenic cycle in donkeys lasted 10.5 days. A similar value was found in mules ( approximately 10.1 days). Considering that the entire spermatogenic process takes approximately 4.5 cycles to be completed, its total duration in donkeys was estimated to last 47.2 days. The results found for mules suggest that the mechanisms involved in the determination of testis structure and function are probably originated from donkeys. Also, the data found for mules suggest that their seminiferous tubules are able to sustain complete spermatogenesis. In this regard, this species is a potential model for transplants of germ cells originated from donkeys and horses or other large animals.

Spermatogenic Cycle Length and Sperm Production in a Feral Pig Species (Collared Peccary, Tayassu tajacu)

“…This observation is in agreement with a number of reports in the literature Neves et al, 2002;Almeida et al, 2006;Costa et al, 2008;Leal and França, 2009), suggesting that phylogeny is strongly related to stage frequencies when grouped in premeiotic and postmeiotic phases. Although the morphology of germ cells in peccaries was very similar to those described for domestic (Swierstra, 1968;França and Cardoso, 1998) and wild pigs (Almeida et al, 2006), the germ cell associations in peccaries resembled more those observed for the wild boar.…”

“…The total duration of spermatogenesis took into account that approximately 4.5 cycles are necessary for this process to be completed from type A spermatogonia to spermiation (Amann and Schanbacher, 1983). Because primary spermatocytes' nuclear volume grows markedly during meiotic prophase (França et al, 1995;Neves et al, 2002;Leal and França, 2006), the size of their nuclei was used to determine more precisely the location of the most advanced labeled germ cell, particularly when these cells were present in stages showing high frequency.…”

Morphological characterization of the testicular cells and seminiferous epithelium cycle in six species of Neotropical bats

“…The similarity in the seminiferous epithelium cycle shared by A. lituratus, A. planirostris, C. perspicillata, P. lineatus and S. lilium has also been observed in other mammalian species such as the puma (Guiã o-Leite et al, 2006), wolf (Bitencourt et al, 2007) and donkey (Neves et al, 2002).…”

Morphometrical changes of the seminiferous tubules and Leydig cells in Assam goats (Capra hircus) from birth to 10 months

“…The seminiferous tubules seem to exert some poorly understood effects on Leydig cell structure and steroidogenic activity (Parvinen 1982). Moreover, macrophages that are present in the testis intertubular tissue have been suggested to enhance Leydig cell steroidogenic activity in vitro (Neaves et al 2002). It has also been stated that a testicular luteinizing hormone releasing hormone-like factor probably secreted by the Sertoli cells has the potential to exert a wide range of stimulatory and inhibitory effects on Leydig cell function (Sharpe 1984).…”