The development of the reproductive ducts and canals in the free-martin with comparison of the normal

Direct observation of hematopoietic progenitor chimerism in fetal freemartin cattle

Background

Cattle twins are well known as blood chimeras. However, chimerism in the actual hematopoietic progenitor compartment has not been directly investigated. Here, we analyzed fetal liver of chimeric freemartin cattle by combining a new anti-bovine CD34 antibody and Y-chromosome specific in situ hybridization.

Results

Bull-derived CD34⁺ cells were detected in the liver of the female sibling (freemartin) at 60 days gestation. The level of bull-derived CD34⁺ cells was lower in the freemartin than in its male siblings. Bull (Y⁺) and cow hematopoietic cells often occurred in separate clusters. Around clusters of Y⁺CD34⁺ cells, Y⁺CD34^- cells were typically observed. The thymi were also strongly chimeric at 60 days of gestation.

Conclusion

The fetal freemartin liver contains clusters of bull-derived hematopoietic progenitors, suggesting clonal expansion and differentiation. Even the roots of the hematopoietic system in cattle twins are thus strongly chimeric from the early stages of fetal development. However, the hematopoietic seeding of fetal liver apparently started already before the onset of functional vascular anastomosis.

Explaining the freemartin: Tandler and Keller vs. Lillie and the question of priority

The correct explanation for the freemartin phenotype in the female twin of a female-male pair in cattle was first reported by Tandler and Keller (1911. Deutsche Tierärzt Wochenschr 19:148-149). This same explanation for the freemartin was independently discovered by Lillie (1916. Science 43:611-613). Today both set of scientists are given credit for this discovery; it is the basis for much of the subsequent work on the developmental basis for sex differentiation in vertebrates. Even though Lillie published after Keller and Tandler, he gets credit for this discovery because: (1) Keller and Tandler published in a veterinary journal and as a consequence their work was not disseminated as broadly throughout the larger scientific community; this problem was compounded by the fact that their definitive 1916 paper was published under wartime conditions during World War I, and (2) Lillie was an influential scientist with a group of graduate students who could elaborate on and extend his work; they published a number of papers on the freemartin. At some point while Lillie was doing his initial work on the freemartin he may have become aware that Keller and Tandler were also working on the freemartin problem; this information may have shaped his decision on when to publish.

Limited Contribution of Circulating Cells to the Development and Maintenance of Nonhematopoietic Bovine Tissues

Bone marrow-derived stem cells appear surprisingly multipotent in experimental settings, but the physiological significance of such plasticity is unclear. We have used sex-mismatched cattle twins with stably chimeric hematopoietic systems to investigate the general extent of integration of circulating cells to the nonhematopoietic cell lineages in an unmanipulated large mammal. The donor-derived (Y+) nonhematopoietic cells in female recipient tissues were visualized by Y-chromosome specific in situ hybridization combined with pan-leukocyte labeling. Y+ leukocytes were frequent in all tissues, but in 11 of 12 animals, average contribution to nonhematopoietic lineages was in any tissue below 1% (in brain <0.001%). Significantly higher integration rate was detected in regenerating granulation tissue. Also, one animal showed a high frequency of nonhematopoietic Y+ cells in several tissues, including intestinal epithelium and mammary gland stroma. In conclusion, circulating cells do not appear significant in the development and maintenance of nonhematopoietic bovine tissues, but may be important in regeneration and other special conditions.

Morphological Observations of Uterine and Vaginal Duplexes with a Developmental Anomaly at the Vaginovestibular Junction in a Japanese Brown Calf

Since a rare anomaly of the female genital tract was defined as uterine and vaginal duplexes with a developmental anomaly at the vaginovestibular junction, it was morphologically examined in detail in a Japanese Brown calf. The genital tract was completely duplicated from the uterus to the vagina just cranial to the vestibule. At the vaginovestibular junction, a hymenal constriction and an aberrant location of the outer urethral orifice were also observed. These anomalies suggest that an error in the complete fusion of the Mullerian ducts and a failure in the correlated development between the Mullerian ducts and the urogenital sinus occurred in the embryonic stage.

Sex difference in target seeking behavior of developing cremaster muscles and the resulting first visible sign of somatic sexual differentiation in marsupial mammals

Cremaster muscles are present in both male and female developing and adult marsupial mammals. They are complex structures and composed of several distinct bundles of striated muscle fibers provided with: (1) a distinct and extensive innervation; (2) a distinct blood vascular supply; (3) a distinct tendineous origin on the anterosuperior iliac spine; and (4) distinct target structures. The muscles thus seem to be separate anatomical entities and not a part of one or more of the layers of the ventral abdominal wall musculature. Cremaster muscles in males are elongated, are larger than in females, and for the most part are a component of the funiculus spermaticus. They insert on the distal part of the tunica vaginalis. The distal parts of the muscles in females are flattened ("fan shaped") and insert over a broad area on the dorsal borders of the mammary glands. Muscles in males have no relation whatsoever to the male mammary glandular rudiments. Muscles in females are attached at the base of the uterine round ligament. The remarkable sex difference in target structures of marsupial cremaster muscles becomes noticeable during perinatal life when outgrowing muscles take a different path in males and females. The initial appearance of this sexually dimorphic trait precedes the sexual differentiation of the genital ducts and external genitalia. In fetal males, the cremaster muscles grow in the direction of the site where scrotal bulges initially appear in the subcutaneous layers and later on the inguinal skin surface. They also take the gubernacular core of the ventral abdominal wall and the attached peritoneal epithelium with them during this outgrowth process. Consequently, this results in the development of a slitlike evagination of the abdominal lumen as the primary step to development of the processus vaginalis, while the testis and adjacent mesonephros and its duct are still attached to the posterior abdominal wall. In fetal females, the outgrowing cremaster muscles pass along the gubernacular core and, subsequently, this structure develops further as the tip (attached to the tubo-uterine junction) of the intra-abdominally protruding and further developing uterine round ligament. The female cremaster muscles grow further into caudal direction to shape a dorsal border of the developing mammary glands. The early onset of this sexually dimorphic outgrowth of cremaster muscles indicates that the "classical hormones" of sexual differentiation (anti-Müllerian hormone [AMH] and steroidal androgens) are not involved in this process. It could thus depend on primary genetic control with male development associated with the male-limited activity of genes on the Y-chromosomes and female development as the default process. Alternatively, the process in males could be under the control of an as yet unidentified third fetal testicular hormone involved in sexual differentiation processes which must then show an unexpectely early (i.e., perinatal) onset of its secretion.

Development of the gubernaculum and processus vaginalis in freemartinism: further evidence in support of a specific fetal testis hormone governing male-specific gubernacular development

BACKGROUND

Freemartinism occurs in some species of ruminants and affects most female bovine fetuses in heterosexual, multiple pregnancies owing to fusion of the chorionic blood circulations soon after implantation. Maldevelopment of the ovaries and Müllerian ducts have been described and recognized as resulting from exposure of their respective primordia to an excess of anti-Müllerian hormone. The present study aimed to analyse the prenatal growth and development of the gubernaculum in freemartins to find out its possible affliction through foetal testis hormones derived from their male co-twin.

METHODS

Histological sections of young and drawings and photographs of further developed freemartins and control male and female bovine foetuses were analysed. The specimens had been collected earlier for analysis of the time course of male and female gonadal and genital development and its impairment associated with freemartinism.

RESULTS

The gubernaculum of 35-40-day-old male and female fetuses was in the initial stage of development and of similar appearance in all specimens. Gubernacula of 60-70-day-old male fetuses differed from those of females of similar age in various respects: the male gubernaculum size was larger and extension of the processus vaginalis was deeper. Freemartins showed an intermediate development with some individuals resembling male and others resembling female agemates. During further development, gubernacula in males developed into muscular cremaster sacs, whereas those in females generally did not develop beyond the size and structural complexity of 70-day-old foetuses. Beyond day 70 of fetal life, gubernaculum development in freemartins definitely showed male characteristics with respect to size and growth of a processus vaginalis with a cremaster muscular wall. The male-like pattern of the outgrowth of the processus vaginalis changed during the second half of prenatal life. Rather than its further deepening as in males, this structure became inverted to become emerging as a papilla-like structure from the inguinal abdomen bottom. An explanation is proposed for this unprecedented inversion, taking into account: (1) the faster and higher reaching rightsided ascent of the kidneys and gonads, (2) the femalelike outgrowth of the cranial gonadal suspensory ligaments, and (3) the absence of scrotum development. The ovaries and mesonephric remnants in developing freemartins, during their ascent together with the kidneys while remaining attached to the bottom of the developing processus vaginalis sacs via the gubernaculum ligament, are proposed to act together to pull up the bottom of the processus vaginalis sacs. From this action, "inverted hernia sacs" result as the irreversible consequence.

CONCLUSION

The data support the concept that foetal testes act, via as an yet unidentified third hormone, to establish malelike development of gubernacula into muscular cremaster sacs. Further work is required to reveal the identity of this hormone. Furthermore, the apparent similarity of the freemartins' inverted processus vaginalis sacs and the fetal rodents' gubernacular cones suggests that the ruminants' and rodents' processus vaginalis are essentially similar structures. Thus there is no longer an urgent need to distinguish between two different types of gubernaculum development and testis descent in rodents and ruminants, respectively, and involving or not fetal gubernacular cones. The present observations may thus contribute to the development of a unified hypothesis for sexually dimorphic development of the gubernaculum throughout the mammalian class.

Programmed cell death in the Müllerian duct induced by Müllerian inhibiting substance

The importance of a secretory product of the fetal testis, Müllerian Inhibiting Substance, in determining the fate of the Müllerian duct in the developing male fetus has been well documented. The present investigation has examined the mechanism of action of Müllerian Inhibiting Substance in the male rat fetus during the course of Müllerian duct degeneration. The action of Müllerian Inhibiting Substance mimics the general morphogenetic phenomenon of "programmed cell death," although important diferences were found compared to the majority of other studies of cell death. The initial morphological event in the degenerating Müllerian duct is an increase in lysosomes within the duct cells. Following loss of polarity and orientation, the duct cells are subsequently removed by invading macrophages from the surrounding mesenchyme. Concommitant with the differentiation of these macrophages, the adjacent mesenchyme assumes a characteristic whorled pattern around the degenerating Müllerian duct. Cytochemical localization of acid phosphatase confirmed the presence of newly formed lysosomes within the Müllerian duct cells and subsequently within the cytoplasm of the invading macrophages.