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. 2019 Apr 2;100(6):1461–1472. doi: 10.1093/biolre/ioz052

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© The Author(s) 2019. Published by Oxford University Press on behalf of Society for the Study of Reproduction.

This is an Open Access article distributed under the terms of the Creative Commons Attribution Non-Commercial License (http://creativecommons.org/licenses/by-nc/4.0/), which permits non-commercial re-use, distribution, and reproduction in any medium, provided the original work is properly cited. For commercial re-use, please contact journals.permissions@oup.com

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Figure 1. — Comparative diagrammatic representations of a mid-sagittal section of spatulate (A, bovine) and falciform (B, rat) spermatozoa. The regional distinctions of the perinuclear theca (PT) of rat spermatozoa depicted in this figure, notably the characterization of the perforatorium, are based on the results of this paper and a culmination of previous work performed in our laboratory. Despite morphological differences, the head of both bovine and rat spermatozoa consists of a nucleus (N, black), acrosome (A, crosshatched), and PT. The acrosome contains an inner acrosomal membrane (IAM) that faces the PT, and an outer acrosomal membrane (OAM) tightly associated with the plasma membrane (PM). The PT is a structurally continuous cytosolic region of the sperm head that encapsulates the entire condensed nucleus, except where the tail implants. (A) A mid-sagittal section of a bovine spermatozoon relative to its three-dimensional structure. The PT of bovine spermatozoa can be divided into the subacrosomal layer (SAL, red) and postacrosomal sheath (PAS, yellow). The SAL occupies the space between the IAM and nuclear envelope, and also includes the outer periacrosomal layer (OPL) along the outer aspect of the equatorial segment (ES) of the acrosome. The PAS extends beyond the SAL in the space between the nuclear envelope and PM, below the acrosome. (B) A mid-sagittal section of a rat spermatozoon, with a superimposed acrosome (light gray) and representative cross-sectional views. In addition to the SAL (with OPL) and PAS, the PT of rat spermatozoa consists of an apical region called the perforatorium (orange). The rat sperm head also contains another apical protrusion called the ventral spur (VS), which is organized into two layers. The acrosomic system of rat differs from bovine in that it contains a ventrally displaced head cap segment (HCS) of which the SAL encapsulates entirely. Note the structural similarity between the caudal cross-sectional images of the rat spermatozoon to the mid-sagittal section of the bovine. M, mitochondria; AX, axoneme. Adapted from Oko and Maravei [4] and Lalli and Clermont [43].