Observations on the reproductive morphology of the female short-beaked echidna, Tachyglossus aculeatus.

Although monotremes diverged from the therian mammal lineage approximately 187 million years ago, they retain various plesiomorphic and/or reptilian-like anatomical and physiological characteristics. This study examined the morphology of juvenile and adult female reproductive tracts across various stages of the presumptive oestrous cycle, collected opportunistically from cadaver specimens submitted to wildlife hospitals during the breeding season. In adult females, ovaries had a convoluted cortex with follicles protruding from the ovarian surface.

Body fat and circulating leptin levels in the captive short-beaked echidna (Tachyglossus aculeatus).

It is possible that the reproductive strategy of the short-beaked echidna is related to seasonal changes in fat deposition and energy availability, regulated by seasonal changes in endocrine function. We predicted that circulating leptin levels would be directly proportional to adiposity during most of the year, but that a change in this relationship would occur during the pre-breeding season to allow increased fat deposition. To test this hypothesis, we made use of a captive colony of echidnas to describe and quantify changes in fat distribution and the adipostatic hormone leptin.

New insights into how to induce and maintain embryonic diapause in the blastocyst.

Embryonic diapause in mammals is a period of developmental pause of the embryo at the blastocyst stage. During diapause, the blastocyst has minimal cell proliferation, metabolic activity and gene expression. At reactivation, blastocyst development resumes, characterised by increases in cell number, biosynthesis and metabolism.

Gut microbiota in the short-beaked echidna (Tachyglossus Aculeatus) shows stability across gestation.

Indigenous gut microbial communities (microbiota) play critical roles in health and may be especially important for the mother and fetus during pregnancy. Monotremes, such as the short-beaked echidna, have evolved to lay and incubate an egg, which hatches in their pouch where the young feeds. Since both feces and eggs pass through the cloaca, the fecal microbiota of female echidnas provides an opportunity for vertical transmission of microbes to their offspring.

Marsupials have monoallelic MEST expression with a conserved antisense lncRNA but MEST is not imprinted.

The imprinted isoform of the Mest gene in mice is involved in key mammalian traits such as placental and fetal growth, maternal care and mammary gland maturation. The imprinted isoform has a distinct differentially methylated region (DMR) at its promoter in eutherian mammals but in marsupials, there are no differentially methylated CpG islands between the parental alleles. Here, we examined similarities and differences in the MEST gene locus across mammals using a marsupial, the tammar wallaby, a monotreme, the platypus, and a eutherian, the mouse, to investigate how imprinting of this gene evolved in mammals.

An evaluation of DNA sample source and molecular markers to determine gender in the short-beaked echidna (Tachyglossus aculeatus).

The short-beaked echidna is sexually monomorphic such that gender identification without veterinary intervention is challenging. The aim of this study was to evaluate and compare the most optimal noninvasive genetic source by extracting echidna genomic DNA (gDNA) from fecal scats, plucked hair, and quills to perform genetic sex testing using a range of molecular markers. Sex determination of 14 captive short-beaked echidnas was determined by amplifying isolated DNA from noninvasive samples, targeting two Y chromosome (male-specific) genes (mediator complex subunit 26 Y-gametologue [CRSPY] and anti-Müllerian hormone Y-gametologue [AMHY]), in addition to four confirmed sex-specific RADseq markers.

Conserved H3K27me3-associated chromatin remodelling allows STRA8 but not MEIOSIN expression in mammalian germ cells.

In Brief: Apart from mice, meiosis initiation factors and their transcriptional regulation mechanisms are largely unknown in mammals. This study suggests that STRA8 and MEIOSIN are both meiosis initiation factors in mammals, but their transcription is epigenetically regulated differently from each other.

Abstract: In the mouse, the timing of meiosis onset differs between sexes due to the sex-specific regulation of the meiosis initiation factors, STRA8 and MEIOSIN.

Getting out of a mammalian egg: the egg tooth and caruncle of the echidna.

In the echidna, after development in utero, the egg is laid in the pouch and incubated for 10 days. During this time, the fetuses develop an egg tooth and caruncle to help them hatch. Using rare and unprecedented access to limited echidna pre- and post-hatching tissues, development of the egg tooth and caruncle were assessed by micro-CT, histology and immunofluorescence.

Validation of a non-invasive assessment technique for quantifying faecal glucocorticoid metabolite concentrations in the short-beaked echidna (Tachyglossus aculeatus).

The monotreme adrenocortical response to stress may not rely as heavily on the hypothalamic-pituitaryadrenal (HPA) axis compared to other mammals. This study aimed to validate a technique in which glucocorticoid metabolites could be quantified non-invasively in short-beaked echidna faeces by examining the secretion of glucocorticoids (GC) using an adrenocorticotrophic hormone (ACTH) challenge on sexually mature captive echidnas. Echidnas were housed individually for 15 days, with the ACTH challenge occurring on day five.

Evolution of the Short Form of DNMT3A, DNMT3A2, Occurred in the Common Ancestor of Mammals.

Genomic imprinting is found in marsupial and eutherian mammals, but not in monotremes. While the primary regulator of genomic imprinting in eutherians is differential DNA methylation between parental alleles, conserved imprinted genes in marsupials tend to lack DNA methylation at their promoters. DNA methylation at eutherian imprinted genes is mainly catalyzed by a DNA methyltransferase (DNMT) enzyme, DNMT3A.

Plasma progesterone secretion during gestation of the captive short-beaked echidna.

This study describes the progesterone profile during pregnancy in sexually mature female captive short-beaked echidnas (Tachyglossus aculeatus aculeatus). Echidnas were monitored daily by video surveillance to confirm key reproductive behaviour. Plasma samples were collected and pouch morphology was assessed three times a week.

The Unique Penile Morphology of the Short-Beaked Echidna, Tachyglossus aculeatus.

Monotremes diverged from therian mammal ancestors approximately 184 million years ago and have a number of novel reproductive characteristics. One in particular is their penile morphology. There are differences between echidna and platypus phalluses, but both are somewhat similar in structure to the reptilian phallus.

Platypus and echidna genomes reveal mammalian biology and evolution.

Egg-laying mammals (monotremes) are the only extant mammalian outgroup to therians (marsupial and eutherian animals) and provide key insights into mammalian evolution. Here we generate and analyse reference genomes of the platypus (Ornithorhynchus anatinus) and echidna (Tachyglossus aculeatus), which represent the only two extant monotreme lineages. The nearly complete platypus genome assembly has anchored almost the entire genome onto chromosomes, markedly improving the genome continuity and gene annotation.

Transient role of the middle ear as a lower jaw support across mammals.

Mammals articulate their jaws using a novel joint between the dentary and squamosal bones. In eutherian mammals, this joint forms in the embryo, supporting feeding and vocalisation from birth. In contrast, marsupials and monotremes exhibit extreme altriciality and are born before the bones of the novel mammalian jaw joint form.

Culture of Mink Preimplantation Embryos.

The reproduction of the mink, Neovison vison, has been extensively studied over the past 70 years. The endocrine control of pregnancy is reasonably well understood, but our understanding of early embryo development is limited. The mink is one of the best characterized mammals for the study of embryonic diapause, but in order to unravel the complex interactions that occur between the blastocyst and the uterus during diapause and reactivation, a defined culture media system that supports growth is essential.

Focal adhesion kinase PTK2 autophosphorylation is not required for the activation of sodium-hydrogen exchange by decreased cell volume in the preimplantation mouse embryo.

SummaryRecovery from decreased cell volume is accomplished by a regulated increase of intracellular osmolarity. The acute response is activation of inorganic ion transport into the cell, the main effector of which is the Na+/H+ exchanger NHE1. NHE1 is rapidly activated by a cell volume decrease in early embryos, but how this occurs is incompletely understood.

New functions for old factors: the role of polyamines during the establishment of pregnancy.

Implantation is essential for the establishment of a successful pregnancy, and the preimplantation period plays a significant role in ensuring implantation occurs in a timely and coordinated manner. This requires effective maternal-embryonic signalling, established during the preimplantation period, to synchronise development. Although multiple factors have been identified as present during this time, the exact molecular mechanisms involved are unknown.

The history of the discovery of embryonic diapause in mammals.

The first incidence of embryonic diapause in mammals was observed in the roe deer, Capreolus capreolus, in 1854 and confirmed in the early 1900s. Since then scientists have been fascinated by this phenomenon that allows a growing embryo to become arrested for up to 11 months and then reactivate and continue development with no ill effects. The study of diapause has required unraveling basic reproductive processes we now take for granted and has spanned some of the major checkpoints of reproductive biology from the identification of the sex hormones to the hypothalamic-pituitary axis to microRNA and exosomes.

The enigma of embryonic diapause.

Embryonic diapause - a period of embryonic suspension at the blastocyst stage - is a fascinating phenomenon that occurs in over 130 species of mammals, ranging from bears and badgers to mice and marsupials. It might even occur in humans. During diapause, there is minimal cell division and greatly reduced metabolism, and development is put on hold.

Inhibition of polyamine synthesis causes entry of the mouse blastocyst into embryonic diapause.

Embryonic diapause is a common reproductive strategy amongst mammals, requiring an intimate cross-talk between the endometrium and the blastocyst. To date, the precise molecular signals responsible are unknown in the mouse or any other mammal. Previous studies in the mink implicate polyamines as major regulators of the control of diapause.

Embryo arrest and reactivation: potential candidates controlling embryonic diapause in the tammar wallaby and mink†.

Embryonic diapause is a period of developmental arrest which requires coordination of a molecular cross-talk between the endometrium and blastocyst to ensure a successful reactivation, but the exact mechanisms are undefined. The objectives of this study were to screen the tammar blastocyst for potential diapause control factors and to investigate the potential for members of the epidermal growth factor (EGF) family to coordinate reactivation. A select number of factors were also examined in the mink to determine whether their expression patterns were conserved across diapause species.

Polyamine-Mediated Effects of Prolactin Dictate Emergence from Mink Obligate Embryonic Diapause.

Embryonic diapause is an evolutionary strategy to ensure that offspring are born when maternal and environmental conditions are optimal for survival. In many species of carnivores, obligate embryonic diapause occurs in every gestation. Reciprocal embryo transplant studies indicate that embryo arrest during diapause is conferred by uterine conditions and is due to a lack of specific factors necessary for continued development.

Embryonic diapause: development on hold.

Embryonic diapause, the temporary suspension of development of the embryo, is a fascinating reproductive strategy that has been frequently exploited across the animal kingdom. It is characterized by an arrest in development that occurs at the blastocyst stage in over 130 species of mammals. Its presumed function is to uncouple mating from parturition, to ensure that both occur at the most propitious moment for survival of the species.

Paf receptor expression in the marsupial embryo and endometrium during embryonic diapause.

The control of reactivation from embryonic diapause in the tammar wallaby (Macropus eugenii) involves sequential activation of the corpus luteum, secretion of progesterone that stimulates endometrial secretion and subsequent changes in the uterine environment that activate the embryo. However, the precise signals between the endometrium and the blastocyst are currently unknown. In eutherians, both the phospholipid Paf and its receptor, platelet-activating factor receptor (PTAFR), are present in the embryo and the endometrium.

Transcriptomic analysis supports similar functional roles for the two thymuses of the tammar wallaby.

Background: The thymus plays a critical role in the development and maturation of T-cells. Humans have a single thoracic thymus and presence of a second thymus is considered an anomaly. However, many vertebrates have multiple thymuses.