Sperm bauplan and function and underlying processes of sperm formation and selection

Abstract

The spermatozoon is a highly differentiated and polarized cell, with two main structures: the head, containing a haploid nucleus and the acrosomal exocytotic granule, and the flagellum, which generates energy and propels the cell; both structures are connected by the neck. The sperm's main aim is to participate in fertilization, thus activating development. Despite this common bauplan and function there is an enormous diversity in structure and performance of sperm cells. For example, mammalian spermatozoa may exhibit several head patterns and overall sperm lengths ranging from ~30 to 350 µm. Mechanisms of transport in the female tract, preparation for fertilization, and recognition and interaction with the oocyte also show considerable variation. There has been much interest in understanding the origin of this diversity, both in evolutionary terms and in relation to mechanisms underlying sperm differentiation in the testis. Here, relationships between sperm bauplan and function are examined at two levels. First, analyzing the selective forces that drive changes in sperm structure and physiology to understand the adaptive values of this variation and impact on male reproductive success. Second, examining cellular and molecular mechanisms of sperm formation in the testis that may explain how differentiation can give rise to such a wide array of sperm forms and functions.

Energy Metabolism and Hyperactivation of Spermatozoa from Three Mouse Species under Capacitating Conditions

“…Competition between spermatozoa to fertilize oocytes [ 1 , 2 , 3 , 4 , 5 ] may influence the evolution of sperm structure [ 6 , 7 ] and performance [ 7 , 8 , 9 ]. Sperm competition may select for faster swimming sperm, which may be the result of changes in various components of sperm morphology [ 10 , 11 , 12 , 13 , 14 ] or bioenergetics [ 15 ].…”

Sun4 is a type II transmembrane protein of the spermatid inner nuclear membrane that forms heteromeric assemblies with Sun3 and interacts with Lamin B3

“…In their role as nucleo-cytoskeletal linkers, LINC complexes represent perfect candidates for involvement in physically connecting these structures to the nucleus, thus enabling a transfer of cytoskeletal shaping forces (Dunleavy et al, 2019; Kmonickova et al, 2020; Kracklauer et al, 2010; Teves and Roldan, 2022). Consistently, in several previous studies, the spermiogenesis specific LINC complex components Sun4 and, very recently, Sun3 were identified as crucial players in sperm head formation, essential for proper NE attachment of the manchette microtubules, correct positioning of other LINC components and finally also for directed nuclear elongation (Calvi et al, 2015; Gao et al, 2020; Pasch et al, 2015; Yang et al, 2018).…”

“…According to current theories, sperm head formation and particularly nuclear elongation are guided by mechanical forces, which are supposed to be generated by highly organized cytoskeletal structures surrounding the nucleus, i.e. the acroplaxome and the manchette (reviewed Dunleavy et al, 2019 andTeves andRoldan, 2022).…”

Alteration of RNA modification signature in human sperm correlates with sperm motility

“…Spermatogenesis in the testicular seminiferous tubules is a complex process that is precisely controlled at the transcriptional, post-transcriptional and translational levels ( Morgan et al , 2021 ). The end products of spermatogenesis, sperm, lose most of their cytoplasm and their histones are extensively replaced with protamines, leading to morphological structures that differ from those of somatic cells ( Amaral et al , 2014 ; Teves and Roldan, 2022 ). Owing to the shut-down of transcription at the end of spermatogenesis and the reduction in cytoplasm, sperm was previously thought to lack RNA ( Monesi, 1964 ; Monesi et al , 1978 ; Miller et al , 2005 ).…”