Direct binding of boar ejaculate and epididymal spermatozoa to porcine epididymal epithelial cells is also needed to maintain sperm survival in in vitro co-culture

The aim of the present study was to compare the influence of cultured epididymal epithelial cells (EEC) from corpus, caput or cauda, oviductal epithelial cells (OEC) and non-reproductive epithelial cells (LLC-PK1) on function and survival of epididymal and ejaculated spermatozoa, in the latter case to determine whether such influence differed between morphologically normal and abnormal spermatozoa. For this purpose, either spermatozoa were directly co-cultured with EEC from caput, corpus, or cauda, OEC and LLC-PK1 cells (experiment 1) or a membrane-diffusible insert was included in these co-cultures (experiment 2). EEC cultured from the three epididymal regions did not differently affect the sperm parameters. Morphologically normal spermatozoa presented a higher ability to bind EEC, OEC, and LLC-PK1 than abnormal spermatozoa with cytoplasmic droplets or with tail/head malformations. Epididymal spermatozoa were more able to bind EEC during the first 24 h of co-culture, while ejaculated spermatozoa presented a higher capacity to bind OEC between 30 min and 3 h of co-incubation. In all cases, the ability to bind to epithelial cells was higher when they were co-cultured with EEC and OEC than with LLC-PK1. After 2 h of co-culture, the viability of epididymal spermatozoa was better maintained when they bound EEC than when they bound OEC. Conversely, the viability of ejaculated spermatozoa was better maintained when bound OEC than when bound EEC after 24 and 48 h of co-culture. Our work, apart from corroborating the involvement of morphologically normal spermatozoa in the formation of sperm reservoir, highlights the importance of direct contact spermatozoa-EEC in maintaining the sperm survival in in vitro co-culture, and also suggests that a specific binding between EEC and epididymal spermatozoa exists.     

Spermatozoa of the shrew, Suncus murinus, undergo the acrosome reaction and then selectively kill cells in penetrating the cumulus oophorus

In the musk shrew, Suncus murinus (and other shrews), the cumulus oophorus is ovulated as a discrete, compact, matrix-free ball of cells linked by specialized junctions. In examining how they penetrate the cumulus, Suncus spermatozoa were observed to first bind consistently by the ventral face over the acrosomal region to the exposed smooth surface of a peripheral cumulus cell. This was apparently followed by point fusions between the plasma and outer acrosomal membranes. Thereafter, spermatozoa without acrosomes were observed within cumulus cells that displayed signs of necrosis, as did some radially neighboring cumulus cells linked by zona adherens and gap junctions. Eventually, penetration of spermatozoa as far as the perizonal space around the zona pellucida left linear tracks of locally necrotic cells flanked by normal cumulus cells. Based on these and previous observations, we conclude that the acrosome reaction in Suncus is always induced by cumulus cells, and that reacted spermatozoa penetrate the cumulus by selective invasion and killing of cumulus cells along a linear track. Loss of the acrosome also exposes an apical body/perforatorium that is covered with barbs that appear to assist reacted fertilizing spermatozoa in binding to the zona pellucida. Because fertilized eggs displayed no other spermatozoa within or bound to the zona, an efficient block to polyspermy must prevent such binding of additional spermatozoa.     

Mechanical constraint converts planar waves into helices on tunicate and sea urchin sperm flagella

The change in the flagellar waves of spermatozoa from a tunicate and sea urchins was examined using high-speed video microscopy to clarify the regulation of localized sliding between doublet microtubules in the axoneme. When the tunicate Ciona spermatozoa attached to a coverslip surface by their heads in seawater or they moved in seawater with increased viscosity, the planar waves of the sperm flagella were converted into left-handed helical waves. On the other hand, conversion of the planar waves into helical waves in the sea urchin Hemicentrotus spermatozoa was not seen in seawater with an increased viscosity as well as in ordinary seawater. However, the sea urchin Clypeaster spermatozoa showed the conversion, albeit infrequently, when they thrust their heads into seawater with an increased viscosity. The chirality of the helical waves of the Clypeaster spermatozoa was right-handed. When Ciona spermatozoa swam freely near a glass surface, they moved in relatively large circular paths (yawing motion). There was no difference in the proportion of spermatozoa yawing in either a clockwise or counterclockwise direction when viewed from above, which was also different from that of the sea urchin spermatozoa. These observations suggest that the planar waves generally observed on the sperm flagella are mechanically regulated, although their stability must depend on the Ca(2+) concentration in the cell. Furthermore, the chirality of the helical waves may be determined by the intracellular Ca(2+) concentration and changed by transmitting the localized active sliding between the doublet microtubules around the axoneme in an alternative direction.     

Interaction between equine semen and the endometrium: the inflammatory response to semen.

Insemination of mares with bacteria-free equine spermatozoa results in an influx of polymorphonuclear neutrophils (PMNs) into the uterine lumen. In vitro studies have demonstrated that equine spermatozoa activate complement, resulting in cleavage of factors C5a and C3b. Since uterine secretion is rich in complement, it is likely that an interaction between spermatozoa and uterine secretion results in C5a-mediated chemotaxis and migration of PMNs into the uterine lumen. Once in the uterine lumen, the PMNs phagocytize bacteria and spermatozoa, which is an important part of sperm elimination from the reproductive tract. It is not clear how the spermatozoa are opsonized, or if phagocytosis of equine spermatozoa is a selective or non-selective process. Breeding-induced endometritis appears to be both up and down regulated by seminal components. A modulatory role on the inflammation has been suggested for equine seminal plasma. Seminal plasma suppressed complement activation, PMN-chemotaxis and phagocytosis in vitro. Preliminary in vivo experiments also support a suppressive role of seminal plasma in breeding-induced endometritis. The duration but not the magnitude of the PMN-influx into the uterine lumen was shortened when seminal plasma was included in an insemination dose. The presence of PMNs in the uterus affects the motion characteristics of spermatozoa in vitro. Both progressive motility and mean path velocity were impaired when spermatozoa were incubated in uterine secretion from mares with ongoing breeding-induced endometritis. The binding of spermatozoa to PMNs was prominent in all samples collected from mares with an ongoing endometritis. The motility remained impaired, but the binding of the spermatozoa to PMNs was reduced when the spermatozoa were incubated in uterine secretion in the presence of seminal plasma. Preliminary characterization of the immune-suppressive component in seminal plasma suggests that it is one or more molecule(s) with a molecular weight between 50 and 100 kDa, partially inactivated by charcoal stripping and partially heat-inactivated at 95 degrees C for 45 min.     

Development of an assay to assess the functional integrity of the human sperm membrane and its relationship to other semen characteristics

The objective of this study was to develop a relatively simple test to evaluate the functional integrity of the membranes of human spermatozoa. As in some other species, human spermatozoa 'swell' under hypo-osmotic conditions due to the influx of water and the expansion of the membranes. A mixture of equal parts of fructose and sodium citrate (150 mosmol) with calculated ionic strength of 0.15 resulted in a maximal number of clearly identifiable swollen spermatozoa. Only small variations were seen when different aliquants of the same semen samples were separately evaluated. A high correlation (r = 0.94) was obtained between expected and observed values of swollen spermatozoa when known amounts of heat-treated spermatozoa, unable to undergo swelling, were added to untreated spermatozoa. A good correlation (r = 0.90) was also observed between the % spermatozoa in a semen sample that were capable of undergoing swelling and the % of denuded hamster oocytes that were penetrated by capacitated spermatozoa from the same semen sample. By contrast, the correlations between % sperm swelling in ejaculates and % normal sperm forms, % motile spermatozoa and % spermatozoa that do not stain with eosin-Y (supravital stain) in the same ejaculates were 0.30, 0.61 and 0.52, respectively. Therefore, the hypoosmotic swelling technique to evaluate the functional integrity of the sperm membrane appears to give high repeatability and accuracy and is closely correlated to the in-vitro fertilizing ability of spermatozoa. It may be a useful addition to the standard semen analysis.     

Sperm utilisation by Melipona quadrifasciata Lepeletier (Hymenoptera, Apidae) queens subjected to multiple mating

Summary In most Hymenoptera species the queen mates once but in a small number of species, multiple matings can occur normally. So, in this study, physogastric M. quadrifasciata queens were mated with a second male to investigate how these queens, naturally inseminated and laying eggs, use spermatozoa stored in their spermatheca, when they are mated with a second male. Results demonstrate that spermatozoa of different males mix in the spermatheca of M. quadrifasciata queens and that there is a gradual increase in the utilisation of spermatozoa of the second male, which could be explained by a competition among spermatozoa of different drones over the way in which spermatozoa are stored in the spermatheca.     

Regulation of sperm flagellar motility by calcium and cAMP-dependent phosphorylation

There is substantial evidence that cAMP-dependent phosphorylation is involved in the activation of motility of spermatozoa as they are released from storage in the male reproductive tract. This evidence includes observations that in vivo activation of motility can be inhibited by protein kinase inhibitors, can be reversed by protein phosphatase treatment of demembranated spermatozoa, and is associated with phosphorylation of sperm proteins, and observations that spermatozoa that have not been activated in vivo can be activated in vitro by cAMP-dependent phosphorylation. Activation in vivo can often be triggered by conditions that increase intracellular pH, but the relevance of this to in vivo activation under natural conditions and the steps between pH increase and cAMP increase have not been fully established. The relationships between changes in the protein substrates for cAMP-dependent phosphorylation and changes in axonemal function are still unknown. Sperm chemotaxis to egg secretions is widespread; in the sea urchin Arbacia, the egg jelly peptide resact has been identified as a chemoattractant. Response to chemoattractants involves changes in asymmetry of flagellar bending waves, and similar changes in asymmetry can be produced in vitro by increases in [Ca++]. Temporal changes in resact receptor occupancy might lead to transient changes in intracellular [Ca++] and the asymmetry of flagellar bending, but many links in this hypothetical sequence remain to be established. Both of these signalling systems offer immediate opportunities for investigations of biochemical pathways leading to easily assayable biological responses. However, complications resulting from interactions between these two systems need to be considered.     

Contact of dog spermatozoa with homologous uterine tube epithelium prolongs flagellar activity in relation to the stage of the estrous cycle

There is scant information about the storage of spermatozoa within the reproductive tract of the bitch. In several species the uterine tube plays a significant role in sperm storage. The present study was performed to investigate the interaction between spermatozoa and the epithelium of the uterine tube, in particular how this interaction might influence the flagellar activity of spermatozoa in relation to the stage of the estrous cycle. Epithelium was harvested from uterine tubes of 24 bitches at various stages of the estrous cycle (estrus, luteal phase or anestrus), and cultured with pooled spermatozoa collected from 6 dogs. Spermatozoa rapidly bound to the epithelial surface by their heads and the majority of attached spermatozoa were motile. The intimate association between spermatozoa and the uterine tube epithelium maintained motility in a manner that was related to the stage of the estrous cycle. Flagellar activity was significantly greater for spermatozoa bound to estrous epithelium than epithelium from the luteal phase or anestrus. On average, approximately 10% of spermatozoa that were attached to the uterine tube epithelium of estrous bitches retained their flagellar activity for 48 h after innoculation. There was no apparent influence of the region of the uterine tube on this effect. These findings suggest that the uterine tube may form a functional spermatozoal reservoir in the bitch.     

Apolipoprotein C-I binds more strongly to phospholipid/triolein/water than triolein/water interfaces: a possible model for inhibiting cholesterol ester transfer protein activity and triacylglycerol-rich lipoprotein uptake

Apolipoprotein C-I (apoC-I) is an important constituent of high-density lipoprotein (HDL) and is involved in the accumulation of cholesterol ester in nascent HDL via inhibition of cholesterol ester transfer protein and potential activation of lecithin:cholesterol acyltransferase (LCAT). As the smallest exchangeable apolipoprotein (57 residues), apoC-I transfers between lipoproteins via a lipid-binding motif of two amphipathic α-helices (AαHs), spanning residues 7-29 and 38-52. To understand apoC-I's behavior at hydrophobic lipoprotein surfaces, oil drop tensiometry was used to compare the binding to triolein/water (TO/W) and palmitoyloleoylphosphatidylcholine/triolein/water (POPC/TO/W) interfaces. When apoC-I binds to either interface, the surface tension (γ) decreases by ~16-18 mN/m. ApoC-I can be exchanged at both interfaces, desorbing upon compression and readsorbing on expansion. The maximal surface pressures at which apoC-I begins to desorb (Π(max)) were 16.8 and 20.7 mN/m at TO/W and POPC/TO/W interfaces, respectively. This suggests that apoC-I interacts with POPC to increase its affinity for the interface. ApoC-I is more elastic on POPC/TO/W than TO/W interfaces, marked by higher values of the elasticity modulus (ε) on oscillations. At POPC/TO/W interfaces containing an increasing POPC:TO ratio, the pressure at which apoC-I begins to be ejected increases as the phospholipid surface concentration increases. The observed increase in apoC-I interface affinity due to higher degrees of apoC-I-POPC interactions may explain how apoC-I can displace larger apolipoproteins, such as apoE, from lipoproteins. These interactions allow apoC-I to remain bound to the interface at higher Π values, offering insight into apoC-I's rearrangement on triacylglycerol-rich lipoproteins as they undergo Π changes during lipoprotein maturation by plasma factors such as lipoprotein lipase.     

Thermotaxis of human sperm cells in extraordinarily shallow temperature gradients over a wide range

On the basis of the finding that capacitated (ready to fertilize) rabbit and human spermatozoa swim towards warmer temperatures by directing their movement along a temperature gradient, sperm thermotaxis has been proposed to be one of the processes guiding these spermatozoa to the fertilization site. Although the molecular mechanism underlying sperm thermotaxis is gradually being revealed, basic questions related to this process are still open. Here, employing human spermatozoa, we addressed the questions of how wide the temperature range of thermotaxis is, whether this range includes an optimal temperature or whether spermatozoa generally prefer swimming towards warmer temperatures, whether or not they can sense and respond to descending temperature gradients, and what the minimal temperature gradient is to which they can thermotactically respond. We found that human spermatozoa can respond thermotactically within a wide temperature range (at least 29-41°C), that within this range they preferentially accumulate in warmer temperatures rather than at a single specific, preferred temperature, that they can respond to both ascending and descending temperature gradients, and that they can sense and thermotactically respond to temperature gradients as low as <0.014°C/mm. This temperature gradient is astonishingly low because it means that as a spermatozoon swims through its entire body length (46 μm) it can sense and respond to a temperature difference of <0.0006°C. The significance of this surprisingly high temperature sensitivity is discussed.     

Identification of sperm morphometric subpopulations in the canine ejaculate: do they reflect different subpopulations in sperm chromatin integrity?

A statistical approach using sequentially principal component analysis (PCA) clustering and discriminant analysis was developed to disclose morphometric sperm subpopulations. In addition, we used a similar approach to disclose subpopulations of spermatozoa with different degrees of DNA fragmentation. It is widely accepted that sperm morphology is a strong indicator of semen quality and since the sperm head mainly comprises the sperm DNA, it has been proposed that subtle changes in sperm head morphology may be related to abnormal DNA content. Semen from four mongrel dogs (five replicates per dog) were used to investigate DNA quality by means of the sperm chromatin structure assay (SCSA), and for computerized sperm morphometry (ASMA). Each sperm head was measured for nine primary parameters: head area (A), head perimeter (P), head length (L), head width (W), acrosome area (%), midpiece width (w), midpiece area (a), distance (d) between the major axes of the head and midpiece, angle (theta) of divergence of the midpiece from the head axis; and four parameters of head shape: FUN1 (L/W), FUN2 (4pi A/P2), FUN3 ((L - W)/(L + W)) and FUN 4 (pi LW/4A). The data matrix consisted of 2361 observations, (morphometric analysis on individual spermatozoa) and 63,815 observations for the DNA integrity. The PCA analysis revealed five variables with Eigen values over 1, representing more than 79% of the cumulative variance. The morphometric data revealed five sperm subpopulations, while the DNA data gave six subpopulations of spermatozoa with different DNA integrity. Significant differences were found in the percentage of spermatozoa falling in each cluster among dogs (p < 0.05). Linear regression models including sperm head shape factors 2, 3 and 4 predicted the amount of denatured DNA within each individual spermatozoon (p < 0.001). We conclude that the ASMA analysis can be considered a powerful tool to improve the spermiogram.     

Cytological Characterization of Self Incompatibility in Gametes of the Ascidian, Ciona intestinalis

We have determined how many elements are involved in the regulation of self-fertilization in the solitary ascidian, Ciona intestinalis that is an incompletely self-sterile species. Animals collected in the field were repeatedly induced to spawn in order to examine their selfing ratios. About 20% of them were self-fertile, although the ratios fluctuated considerably among respective spawnings. Naturally or acid-induced self-fertile gametes required much longer time for selfing than that for crossing. Egg-suspending seawater (egg water) as such activated sperm motility, but it lowered conspicuously the self-fertilization ratio. Self-sterile spermatozoa could scarcely bind to the vitelline coat (VC) of glycerinated autologous eggs. or in case they bound well to it the sperm flagella ceased to beat within five min of the 'insemination'. The staining of sectioned gametes with DAPI, a fluorescent dye of DNA, showed that in selfing the spermatozoa could hardly penetrate the VC even though they bound well to it. The results of this study show that the block of self-fertilization can be classified into four elements from a phenomenal viewpoint, such as egg water, low affinity of sperm-VC binding, inactivation of bound sperm and difficulty in sperm penetration through the VC.     

Water and Ionic Fluxes Inside the Egg

The water/water and water/gas interfaces of the developing embryoare described. During incubation three main compartments arepresent the subgerminal amniotic and allantoic fluids. The formationcomposition and regulation of these solutions are consideredas examples of the water/water interfaces. Evaporative waterloss across the eggshell is considered as an example of a water/gasinterface. The effects of this phenomenon are considered ashaving been oversimplified in the past because they ignore phasechanges (condensing of water vapour) and the ability of theembryo to regulate its development according to the suppliesavailable.     

Validation of a rapid, large-scale assay to quantify ATP concentration in spermatozoa

Quantification of ATP content in spermatozoa is a useful assay for evaluating sperm function; however, most detection methodology relies on assessing single samples. We have developed and validated a highly repeatable assay that permits simultaneous measurement of up to 78 samples. A key feature of this assay includes combination of a phosphatase inhibition and ATP extraction step that permits maximal detection of ATP and sample storage at -20 degrees C prior to assay. The assay was validated for spermatozoa from three different species, including turkey, rooster and boar. The sensitivity of the assay differed between avian and mammalian spermatozoa, with 2.5 x 10(6) spermatozoa being the lowest number of turkey and rooster spermatozoa that could be assayed compared to 2.5 x 10(5) boar spermatozoa. Concentrations of ATP in fresh turkey semen ranged from 2.14 to 15.6 nmol/10(9) spermatozoa; similarly, freshly collected rooster semen contained from 2.16 to 21.4 nmol ATP/10(9) spermatozoa. Evaluation of turkey semen that had been stored at 4 degrees C for 24 h revealed a decline in ATP concentrations (2.35 +/- 0.34 nmol ATP/10(9) spermatozoa). Likewise, cryopreserved rooster spermatozoa contained lower concentrations of ATP (0.05 +/- 0.01 nmol ATP/10(9) spermatozoa) than non-stored spermatozoa. Boar spermatozoa contained similar concentrations of ATP, whether fresh (74.2 +/- 8.1 pmol ATP/10(6) spermatozoa), stored for 1 day (77.0 +/- 8.1 pmol ATP/10(6) spermatozoa) or 5 days (81.96 +/- 8.1 pmol ATP/10(6) spermatozoa). For all three species, assay variation was low (inter-assay, 0.66-1.9% CV; intra-assay, 1.3% CV).     

A Pressure-dependent Model for the Regulation of Lipoprotein Lipase by Apolipoprotein C-II

Apolipoprotein C-II (apoC-II) is the co-factor for lipoprotein lipase (LPL) at the surface of triacylglycerol-rich lipoproteins. LPL hydrolyzes triacylglycerol, which increases local surface pressure as surface area decreases and amphipathic products transiently accumulate at the lipoprotein surface. To understand how apoC-II adapts to these pressure changes, we characterized the behavior of apoC-II at multiple lipid/water interfaces. ApoC-II adsorption to a triacylglycerol/water interface resulted in large increases in surface pressure. ApoC-II was exchangeable at this interface and desorbed on interfacial compressions. These compressions increase surface pressure and mimic the action of LPL. Analysis of gradual compressions showed that apoC-II undergoes a two-step desorption, which indicates that lipid-bound apoC-II can exhibit at least two conformations. We characterized apoC-II at phospholipid/triacylglycerol/water interfaces, which more closely mimic lipoprotein surfaces. ApoC-II had a large exclusion pressure, similar to that of apoC-I and apoC-III. However, apoC-II desorbed at retention pressures higher than those seen with the other apoCs. This suggests that it is unlikely that apoC-I and apoC-III inhibit LPL via displacement of apoC-II from the lipoprotein surface. Upon rapid compressions and re-expansions, re-adsorption of apoC-II increased pressure by lower amounts than its initial adsorption. This indicates that apoC-II removed phospholipid from the interface upon desorption. These results suggest that apoC-II regulates the activity of LPL in a pressure-dependent manner. ApoC-II is provided as a component of triacylglycerol-rich lipoproteins and is the co-factor for LPL as pressure increases. Above its retention pressure, apoC-II desorbs and removes phospholipid. This triggers release of LPL from lipoproteins.     

Binding of a 15 kDa glycoprotein from spermatozoa of boars to surface of zona pellucida and cumulus oophorus cells.

A highly purified 15 kDa glycoprotein isolated from ejaculated spermatozoa was used to raise antisera in female rabbits. An indirect immunofluorescence technique was used to detect the antigen in the seminal vesicle tissue and on the acrosomes of ejaculated, native and capacitated, boar spermatozoa. No immunoreactivity was detected on cells of the seminiferous tubules (spermatogonia, spermatocytes, and spermatids), on spermatozoa in the ductus epididymis and in cells of the epididymal and testicular tissues. These observations support the view that the 15 kDa protein is produced in the seminal vesicle secretory epithelium, and is attached to the sperm plasma membrane during the exposure of spermatozoa to seminal vesicle compounds. The observations that the antigen remained on the acrosome of ejaculated spermatozoa after capacitation and blocked sperm-oocyte binding in vitro suggest that the antigen plays a role in sperm-egg interactions. The strong immunoreactivity exhibited by cumulus cells after incubation of antisera with the porcine egg surrounded by cumulus cells shows the possible importance of the 15 kDa glycoprotein for contact of spermatozoa with cells of the cumulus oophorus surrounding the egg.     

Using computational modeling to investigate sperm navigation and behavior in the female reproductive tract

The processes by which individual sperm cells navigate the length and complexity of the female reproductive tract and then reach and fertilize the oocyte is fascinating. Numerous complex processes potentially influence the transport of spermatozoa within the tract, resulting in a regulated supply of spermatozoa to the oocytes at the site of fertilization. Despite significant differences between species, breeds, and individuals, these processes converge to ensure that a sufficient number of high quality spermatozoa reach the oocytes, resulting in successful fertilization without a significant risk of polyspermy. Different factors, such as the physical complexity of the oviductal environment, changing swimming patterns, capacitation, chemotactic and thermotactic attraction, attachment and detachment from the oviductal epithelium, interactions with local oviductal secretions, individual variations in spermatozoa and subpopulations, peristaltic contractions, and the movement of fluid have all been theorized to influence the transport of spermatozoa to the site of fertilization. However, the predominance of each factor is not fully understood. Computational modeling provides a useful method for combining knowledge about the individual processes in complex systems to help understand the relative significance of each factor. The process of constructing and validating an agent-based computational model of sperm movement and transport within the oviductal environment is described in this report. Spermatozoa are modeled as individual cells with a set of behavioral rules defining how they interact with their local environment and regulate their internal state. The inclusion or potential exclusion of each factor is discussed, along with problems identifying parameters and defining behavioral rules from available literature. Finally, the benefits and limitations of the model are described.     

Molecular dynamics study of the folding of hydrophobin SC3 at a hydrophilic/hydrophobic interface

Hydrophobins are fungal proteins that self-assemble at hydrophilic/hydrophobic interfaces into amphipathic membranes. These assemblages are extremely stable and posses the remarkable ability to invert the polarity of the surface on which they are adsorbed. Neither the three-dimensional structure of a hydrophobin nor the mechanism by which they function is known. Nevertheless, there are experimental indications that the self-assembled form of the hydrophobins SC3 and EAS at a water/air interface is rich with beta-sheet secondary structure. In this paper we report results from molecular dynamics simulations, showing that fully extended SC3 undergoes fast (approximately 100 ns) folding at a water/hexane interface to an elongated planar structure with extensive beta-sheet secondary elements. Simulations in each of the bulk solvents result in a mainly unstructured globular protein. The dramatic enhancement in secondary structure, whether kinetic or thermodynamic in origin, highlights the role interfaces between phases with large differences in polarity can have on folding. The partitioning of the residue side-chains to one of the two phases can serve as a strong driving force to initiate secondary structure formation. The interactions of the side-chains with the environment at an interface can also stabilize configurations that otherwise would not occur in a homogenous solution.     

Sperm phenotype and its relationship to somatic and germ line genotype: a study using mouse aggregation chimeras.

The mouse strains C3H/Bi McL and C57BL/McL were shown to have markedly different spermatozoa, and, by combining four different sperm dimensions by means of a discriminant function, it was possible to identify individual spermatozoa from the two strains with a calculated misclassification probability of 2.1%. Hybrids had intermediate sperm discriminant values.The sperm from five C3HC57 chimeras were characterized using the discriminant function, and it was found that one chimera had C57-like sperm, another had C3H-like sperm, while each of the other three had sperm of both phenotypes. In no case did the sperm populations of chimeras resemble those of hybrids. A detailed analysis of the sperm dimensions of the chimeras showed that the differences between the two populations of sperm and the variances of these populations are the same as for C3H and C57 sperm populations from pure strain mice.These observations imply that sperm dimensions are determined at the level of individual spermatozoa but do not differentiate between intrinsic (germ line) and extrinsic (Sertoli cell) control. However, the proportions of C3H-type and C57-type sperm in the chimeras were found to be correlated with the proportions of C3H-derived and C57-derived offspring but not with the proportions of C3H and C57 cells in somatic tissues. It is argued that the differences in sperm dimensions between the two strains are due to genes expressed through the germ line.