Reproductive Biology in Egg-Laying Mammals

@article{Grtzner2008ReproductiveBI,
  title={Reproductive Biology in Egg-Laying Mammals},
  author={Frank Gr{\"u}tzner and Brett Nixon and R.C. Jones},
  journal={Sexual Development},
  year={2008},
  volume={2},
  pages={115 - 127}
}
The duck-billed platypus and short-beaked echidna are iconic species in Australia. Their morphology and physiology have puzzled scientists all over the world for more than 200 years. Recent genetic studies, particularly the platypus whole-genome sequencing project, have revealed the molecular basis of some of the extraordinary characteristics of monotremes. This and other works demonstrate the great value of research on our most distantly related mammalian relatives for comparative genomics and… 

Figures from this paper

The enigma of the platypus genome

Some of the key findings of the analysis of the platypus genome are discussed and point to new findings and future research directions, which illustrate the broad impact of the monotreme biology and mammalian genome evolution.

Platypus Genome Provides Unique Insights into Early Mammalian Evolution and Monotreme Biology

The recently completed draft genome of the duck-billed platypus fills this gap in comparative genomics, and provides unique insights into the evolution of mammalian genes, regulatory mechanisms and nonprotein-coding sequences.

Evolution and Organization of Monotreme Sex Chromosomes

Monotremes have an unusually complex sex chromosome system which shares extensive homology to bird sex chromosomes and no homologies to sex chromosomes in other mammals, which raises fundamental questions about its evolution, meiotic organization and dosage compensation and about sex determination in monotremees.

Sperm Competition, Sexual Selection, and the Diverse Reproductive Biology of Osteoglossiformes.

It is suggested that the patterns seen in osteoglossiform reproduction are a microcosm of teleost reproductive diversity, potentially signifying the genetic plasticity that contributed to the adaptive radiation ofteleost fishes.

Gonadal Asymmetry and Sex Determination in Birds

The morphological development and molecular basis of this unusual asymmetry in the chick embryo are described, the implications for avian sex determination are considered, and the possible biological reasons why many birds have adopted a single-ovary system are discussed.

Platypus chain reaction: directional and ordered meiotic pairing of the multiple sex chromosome chain in Ornithorhynchus anatinus.

This work has analysed the pairing dynamics of specific sex chromosome pseudoautosomal regions in platypus spermatocytes during prophase of meiosis I and shows a highly coordinated pairing process that begins at the terminal Y5 chromosome and completes with the union of sex chromosomes X1Y1.

The Testatin/Cres subgroup of family 2 cystatins in sexual development

The evolutionary origin of the Testatin/Cres subgroup genes to the split between Marsupials and placental mammals is localized and a model for the evolution of these genes illustrates that they constitute a dynamic group of genes, which has undergone several gene expansions.

References

SHOWING 1-10 OF 130 REFERENCES

Echidna: Extraordinary Egg-Laying Mammal

The authors reveal some fascinating new findings, showing how echidnas are masters of their environment, and not simply some sort of mammal ‘test model’ that went wrong.

Adaptations of the short-beaked echidna Tachyglossus aculateus for sperm production, particularly in an arid environment.

It is suggested that T. aculateus is also specialised for sperm competition, and the size of their testes and number of extragonadal sperm compared with other mammals are indicative that they are involved in sperm competition.

Bird-like sex chromosomes of platypus imply recent origin of mammal sex chromosomes.

In therian mammals (placentals and marsupials), sex is determined by an XX female: XY male system, in which a gene (SRY) on the Y affects male determination. There is no equivalent in other amniotes,

The multiple sex chromosomes of platypus and echidna are not completely identical and several share homology with the avian Z

A comparative study of platypus and echidna by chromosome painting and comparative gene mapping shows that monotremes have a unique XY sex chromosome system that shares some homology with the avian Z.

A platypus' eye view of the mammalian genome.

Spermiogenesis and spermiation in a monotreme mammal, the platypus, Ornithorhynchus anatinus

The ultrastructure of 16 steps of spermatid development is described and provides a basis for determining the kinetics of sPermatogenesis.

How did the platypus get its sex chromosome chain? A comparison of meiotic multiples and sex chromosomes in plants and animals

It is concluded that the evolutionary conservation of the chain in monotremes, the structural properties of the translocated chromosomes and the highly accurate segregation at meiosis make the platypus system remarkably different from meiotic multiples in other species.

Sex determination in platypus and echidna: autosomal location of SOX3 confirms the absence of SRY from monotremes

The autosomal localization of SOX3 in monotreme mammals, as well as non-mammal vertebrates, implies that SRY is absent in Prototheria and evolved later in the therian lineage 210-180 million years ago, implying sex determination in platypus and echidna must therefore depend on another male-determining gene(s) on the Y chromosomes, or on the different dosage of a gene on the X chromosomes.

Postnatal development of the reproductive system in the grey short-tailed opossum, Monodelphis domestica

In summary, postnatal reproductive tract development and gonadal descent has been examined in this important biomedical model, where differentiation of the wolffian and müllerian ducts takes place after gonadal differentiation, according to the normal eutherian pattern.

Trophoblast and hypoblast in the monotreme, marsupial and eutherian mammal: evolution and origins

It is suggested that the gross differences can be explained by two relatively small evolutionary timing changes affecting cell adhesion patterns and the polarisation of developmentally significant information.
...