MALE ANATOMY INTRODUCTION - Body shape, behavior and propagation (Part I)

General Information -Body shape -Male behavior -Generating male stocks -Boy or girl? Sexing C.elegans larvae -Back to Contents

General Information

In addition to hermaphrodites (5AA;XX), C. elegans produces a male sex (5AA;X0). Males differ from hermaphrodites in their gross morphology, many aspects of their anatomy and expression of certain behaviors. Most sex-specific differences are established after hatching, over the course of larval development (described in MALE HANDBOOK-Introduction-Part II). Under the stereomicroscope, the adult male can be distinguished from the hermaphrodite by its slim body, clear (white) ventral gonad and distinctive tail, which bears a copulatory apparatus (MaleFIG1A,1B). Adult males are smaller than aged-matched hermaphrodites, despite the fact that they are composed of more somatic nuclei. The greater girth and length of hermaphrodites appears to be due, in part, to their voluminous gonad although other tissues, such as the hypodermis, may contribute (Hodgkin, 1988). The cell lineage of the male, from egg to adult, has been determined and, like the hermaphrodite, appears to be largely invariant between individuals (Sulston and Horvitz, 1977; Sulston et al., 1980; Sulston et al., 1983). In contrast to the hermaphrodite, however, the connectivity of the male nervous system is only partially described (Sulston et al., 1980). Efforts to reconstruct the male nervous system from serial EM sections as per the hermaphrodite (White et al., 1986, MOW; Hall and Russell, 1991), have recently resumed ("The Male Wiring Project"). Data emerging from this project will be incorporated into the male handbook and Individual neurons pages.

Body Shape

At hatching male larvae have the same cylindrical body form as hermaphrodites. However, as they progress through the larval stages and their sexual organs develop, the shape of their posterior changes (Sulston and Horvitz, 1977; Sulston et al., 1980; Nguyen et al., 1999). The pointed (leptoderan) tail tip retracts generating a blunt-ended (peloderan) tail. The male's copulatory apparatus, which consists of several structures, is also established in the tail. A lateral extension of the cuticle, called the fan, extends from the tail and holds nine bilateral pairs of sensory rays (MaleFIG1A,1C,1D). On the ventral surface of the tail, on either side of the cloaca (male anus), are the hook sensillum and postcloacal sensilla (PCS) (MaleFIG1D). The cloaca is connected internally to a chamber called the proctodeum (a modified rectum), which in turn is linked to the intestine and the gonad (MaleFIG1A). The proctodeum houses prong-like structures called the spicules, two sensilla covered in a hard, sclerotic cuticle. The rays, hook, PCS and spicules have been shown to have specific roles in guiding the execution of male mating behavior (MaleFIG2; Liu and Sternberg, 1995).

Male behavior

Males differ from hermaphrodites in their expression of a number of behaviors including regulation of defecation (Reiner and Thomas, 1995), response to media conditioned by the same- versus opposite sex (Simon and Sternberg, 2002; White et al., 2003), mate-searching (Emmons and Lipton, 2003) and perhaps most striking of all, mating behavior (see Mating Movie MaleFig2B; Emmons and Sternberg, 1997). The sex-specific or sexually dimorphic cells underlying expression of some of these behaviors have been identified (Reiner and Thomas, 1995; Loer and Kenyon, 1993; Liu and Sternberg, 1995; Table 1- Emmons and Sternberg, 1997; Garcia et al., 2001).

Generating male stocks

Males (5AA;X0) arise from fusion of nullo-X gametes (gametes that lack an X chromosome) and normal X-bearing gametes. Nullo-X gametes are generated by spontaneous non-disjunction of the X chromosome during meiosis in the germ line. This, however, occurs rarely in the hermaphrodite germ line. Consequently, males occur infrequently in cultures propagated by hermaphrodite self-fertilization (ca. 0.1-0.2%; Ward and Carrel,1979; Hodgkin and Doniach, 1997). Examining male anatomy or gene expression patterns on any significant scale from such cultures is therefore impractical. Males, however, can be generated in high numbers using him mutations (high incidence of males) or by mating. him mutations increase the frequency of X-non-disjunction in the hermaphrodite germ line and consequently the number of males arising through self-fertilization (ca. 30%). him-5 and him-8 mutations are typically used as these have no apparent deleterious effects on anatomy or behavior in either sex (Hodgkin et al., 1979). Reproduction by mating produces a high frequency of males, in part, because male sperm contains an equal frequency of nullo-X and X-bearing gametes and because male-derived sperm out-compete hermaphrodite sperm in the fertilization of oocytes (Ward and Carrel,1979). There are several methods for generating parent males (P0s) for a mating from non-him strains (1) heat-shock treatment (Sulston and Hodgkin, 1988: set up 3 plates, each containing 6 L4 stage hermaphrodites. Incubate at exactly 30°C: 1 plate for 5hrs, 1 for 5.5hrs and 1 for 6hrs); (2) Exposure to ethanol (Lyons and Hecth, 1997); (3) him-14 dsRNA feeding (Killian and Hubbard, 2001). Alternatively, P0s can be taken from him-5 or him-8 strains. Use of this approach has the added advantage of allowing him-5 or him-8 F3* homozygous lines to be recovered that will produce approximately 30% male progeny in subsequent generations without the need for crossing (*only hermaphrodites that are him homozygous can produce male off-spring by selfing and so during strain construction the first him males do not appear until the F3 generation).

Boy or girl? Sexing C. elegans larvae

For some studies it may be necessary to examine or recover males from mixed-sex populations before gross anatomical differences between the sexes become apparent. Sulston and Horvitz (1977) identified three criteria for distinguishing the sexes at L1 (MaleFig3A). In the rectal epithelium, for example, B and Y cells have larger nuclei in the male (MaleFig3B) and start dividing at late-L1. In hermaphrodites B does not divide and Y becomes the PDA neuron.

In early L3, the male gonad takes a different path of elongation from that of the hermaphrodite (MaleFIG4A; Kimble and Hirsh, 1979; Hedgecock et al., 1987). Also from L3 onwards, sex-specific differences become apparent in the tail that can be readily detected under the stereomicroscope (MaleFIG4B, 4C). In males the white or clear area at the tail tip starts to expand anteriorly and tail becomes increasingly swollen due to cell proliferation (Sulston and Horvitz, 1977; Sulston et al., 1980). By mid L4, remodeling of the tail begins, starting with resorption of the tail tip (Sulston and Horvitz, 1977; Sulston et al., 1980; Nguyen et al., 1999).

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