Anatomical evidence for the epididymis as the prime mover in the evolution of the scrotum

Bedford, J. M.

doi:10.1002/aja.1001520404

Cited by 112 publications

(51 citation statements)

References 67 publications

(1 reference statement)

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“…This is illustrated to an extreme degree in vespertilionid bats in which an interfemoral membrane provides support for the cauda to extend far beyond the semi-inguinal testis. Equally significant, in a diverse variety of mammals whose scrotal testes are furred, the adjacent region overlying the cauda displays a circumscribed baldness (Bedford 1978). This configuration, as well as occasional examples of discrete pigmentation over the cauda (e.g.…”

Section: The Scrotummentioning

confidence: 99%

Singular features of fertilization and their impact on the male reproductive system in eutherian mammals

Bedford

2014

Reproduction

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Therian (marsupial and eutherian) mammals have evolved a suite of novel reproductive features -seen variously in their gametes, the steps of fertilization and the male reproductive tract -whose adaptive significance remains unclear. Present evidence for the betterunderstood eutherian mammals suggests that the 'prime mover' in their evolution has been the character of the egg coat, with other such features being adaptations to the consequences of this. Its elastic thickness allows the zona pellucida to stretch to a variable degree and yet remain around the blastocyst during much or all of its expansion before implantation, but its character represents an unusual challenge for spermatozoa. Novel aspects of the acrosome related to this challenge enable it to maintain a relatively prolonged binding after the onset of the acrosome reaction, and the structure, shape and behaviour of the sperm head point to physical thrust as a major element of zona penetration -with the unique configuration of gamete fusion as a sequela of this strategy. In the male, such adaptations are reflected in sperm head formation in the testis and in sperm maturation in the epididymis involving at least the sperm head's structure, plasmalemma and acrosome. This complexity allied to a slow epididymal sperm transport, a relatively modest sperm production and the brief life span of mature spermatozoa kept above the cauda epididymidis could account for the evolution of the sperm storage function -a development seemingly linked, in turn, to the need for sperm capacitation and scrotal evolution.Reproduction (2014) 147 R43-R52

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Section: The Scrotummentioning

confidence: 99%

Singular features of fertilization and their impact on the male reproductive system in eutherian mammals

Bedford

2014

Reproduction

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“…Our observation of defective development of the smooth musculature in the epididymis in Insl3 homozygous mutant mice, combined with its high intraabdominal undescended position, supports previous observations regarding the importance of intact epididymis morphology and function for descent of the epididymotesticular unit. Finally, the fact that there are animals with descended epididymes (chinchilla) but undescended testes, but no mammals with descended testes and undescended epididymes, underscores the necessity of epididymal, rather than testicular, descent (16).…”

Section: A C Bmentioning

confidence: 99%

Insulin 3-like hormone and its role in epididymo-testicular descent

Hadžiselimović¹,

Adham

2007

Int. braz j urol.

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Purpose: The role of insulin 3-like (Insl3) hormone signaling in the testicular descent process has been demonstrated. The purpose of the present study was to evaluate epididymal development in Insl3-deficient mice. Materials and Methods: Heterozygous and homozygous Insl3 mutants of a mixed CD1 X 129/Sv genetic background were generated by breeding Insl3 -/-females with Insl3 +/-males, and their genotypes were determined by polymerase chain reaction. On the first postnatal day, newborn males were sacrificed, embedded in paraffin, and cut in 4 µm sections. Sections were stained with hematoxylin/eosin and immunoreacted with anti-α actin antibody.Results: An analysis of stained sections indicated an arrest in the development of the epididymis in all homozygous mice. The cauda and corpus of the epididymis were undersized. Compared to the heterozygous epididymis, the homozygous epididymis had fewer peritubular layers and dwarfish musculature. We confirmed this with immunostaining with monoclonal antibodies against α-smooth muscle actin. Conclusion: Defective development of the smooth musculature in the epididymis of Insl3 homozygous mutant mice, combined with its high intraabdominal undescended position, supports previous observations regarding the importance of intact epididymis morphology and function for descent of the epididymo-testicular unit.

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“…These features include a discrete peri-caudal baldness (Fig. 6 -white-tailed rat, bushbaby, laboratory rat, Clun Forest ram) (Bedford, 1978;Contreras and Rosenmann, 1982), as well as pigmentation of that pericaudal region (bushbuck, red fox), its exaggerated dartos muscle activity, and insulation of the cooler cauda from the warmer testis by a fat pad (rat, degu). Whereas these features all favour cooling of the cauda, in no case does the form of the scrotum or the disposition of its contents seem directed to preferential cooling of the testis.…”

Section: Sperm Capacitationmentioning

confidence: 99%

Puzzles of mammalian fertilization and beyond

Bedford¹

2008

Int. J. Dev. Biol.

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A complexity imposed on the events of conception during the evolution of eutherian mammals is reflected not only in the placenta but also in a series of gamete-related novelties that involve the design of sperm and eggs, their interactions leading to fertilization, epididymal function, and even the scrotal state. While their functional significance has been difficult to determine, I suggest on the basis of present evidence that the genesis of these novel features relates ultimately to changes in the egg associated with nidation, that they imply a new fertilization strategy, and that most are causally linked -a major first 'domino' being the formidable zona pellucida. The eutherian zona pellucida stands out by virtue of an elastic resilience and thickness which allow it to stretch around the expanding blastocyst. However, this quality of the zona together with its relative protease-insensitivity creates a physical challenge which appears to have determined the design of the sperm head, its behaviour at fertilization, and indirectly even the pattern of sperm maturation in the epididymis. In turn, that pattern appears to have evoked the development of the sperm storage function of the cauda region, with both sperm capacitation and the scrotal state as ultimate legacies of this. Coincidentally, the vulnerability of the small yolkless egg to polyspermy appears to have selected for a unique parsimonious pattern of sperm transport in the Fallopian tube, and possibly for the role of the cumulus oophorus as a sperm sequestering device. These ideas are supported generally by evidence from marsupials, as well as by the deviant patterns seen in some insectivorous mammals.

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Anatomical evidence for the epididymis as the prime mover in the evolution of the scrotum

Cited by 112 publications

References 67 publications

Singular features of fertilization and their impact on the male reproductive system in eutherian mammals

Singular features of fertilization and their impact on the male reproductive system in eutherian mammals

Insulin 3-like hormone and its role in epididymo-testicular descent

Puzzles of mammalian fertilization and beyond

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