Feature selectivity and invariance in marsupial primary visual cortex.

A fundamental question in sensory neuroscience revolves around how neurons represent complex visual stimuli. In mammalian primary visual cortex (V1), neurons decode intricate visual features to identify objects, with most being selective for edge orientation, but with half of those also developing invariance to edge position within their receptive fields. Position invariance allows cells to continue to code an edge even when it moves around.

Inhibiting p38α and -β MAPK Affects Testis Development in the Marsupial Tammar Wallaby.

Introduction: The MAPK genes are critical for gonadal differentiation in eutherian mammals, but their role in marsupial mammals is unknown. Characterisation and phylogenetic analyses of the tammar wallaby MAPK genes show these genes are highly conserved with their orthologues in mammalian and non-mammalian species.

Methods: We cultured sexually indifferent tammar gonads in the presence of p38α and -β MAPK inhibitor, SB202190.

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.

Extant and extinct bilby genomes combined with Indigenous knowledge improve conservation of a unique Australian marsupial.

Ninu (greater bilby, Macrotis lagotis) are desert-dwelling, culturally and ecologically important marsupials. In collaboration with Indigenous rangers and conservation managers, we generated the Ninu chromosome-level genome assembly (3.66 Gbp) and genome sequences for the extinct Yallara (lesser bilby, Macrotis leucura).

The structure of the TH/INS locus and the parental allele expressed are not conserved between mammals.

Parent-of-origin-specific expression of imprinted genes is critical for successful mammalian growth and development. Insulin, coded by the INS gene, is an important growth factor expressed from the paternal allele in the yolk sac placenta of therian mammals. The tyrosine hydroxylase gene TH encodes an enzyme involved in dopamine synthesis.

Atrazine disorganises laminin formation and reduces cell numbers in the tammar testis during early differentiation.

In Brief: Atrazine, like oestrogen, disorganises laminin formation and reduces the number of germ cells and Sertoli cells in the developing testes of the tammar wallaby. This study suggests that interfering with the balance of androgen and oestrogen affects the integrity of laminin structure and testis differentiation.

Abstract: The herbicide atrazine was banned in Europe in 2003 due to its endocrine disrupting activity but remains widely used.

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.

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.

The alternate pathway of androgen metabolism and window of sensitivity.

Since the discovery in 1968 that dihydrotestosterone (DHT) is a major mediator of androgen action, a convincing body of evidence has accumulated to indicate that the major pathway of DHT formation is the 5α-reduction of circulating testosterone in androgen target tissues. However, we now know that DHT can also be formed in peripheral tissues by the oxidation of 5α-androstane-3α,17β-diol (adiol). This pathway is responsible for the formation of the male phenotype.

Divergent patterns of meiotic double strand breaks and synapsis initiation dynamics suggest an evolutionary shift in the meiosis program between American and Australian marsupials.

In eutherian mammals, hundreds of programmed DNA double-strand breaks (DSBs) are generated at the onset of meiosis. The DNA damage response is then triggered. Although the dynamics of this response is well studied in eutherian mammals, recent findings have revealed different patterns of DNA damage signaling and repair in marsupial mammals.

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.

The swan genome and transcriptome, it is not all black and white.

Background: The Australian black swan (Cygnus atratus) is an iconic species with contrasting plumage to that of the closely related northern hemisphere white swans. The relative geographic isolation of the black swan may have resulted in a limited immune repertoire and increased susceptibility to infectious diseases, notably infectious diseases from which Australia has been largely shielded. Unlike mallard ducks and the mute swan (Cygnus olor), the black swan is extremely sensitive to highly pathogenic avian influenza.

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.

Comparing the potential for maternal-fetal signalling in oviparous and viviparous lizards.

The evolution of a placenta requires several steps including changing the timing of reproductive events, facilitating nutrient exchange, and the capacity for maternal-fetal communication. To understand the evolution of maternal-fetal communication, we used ligand-receptor gene expression as a proxy for the potential for cross-talk in a live-bearing lizard () and homologous tissues in a related egg-laying lizard (). Approximately 70% of expressed ligand/receptor genes were shared by both species.

Investigating the utility of using fecal hormone metabolites as a reproductive management tool for captive short-beaked echidnas (Tachyglossus aculeatus).

This study demonstrates the utility of the analysis of fecal hormone metabolites as a reproductive management tool for captive short-beaked echidnas. Over three breeding seasons daily fecal samples were collected from female echidnas (n = 8) that were monitored continuously by video surveillance to confirm key reproductive events. Fecal progesterone metabolite concentrations were elevated above baseline values (448.

Orientation pinwheels in primary visual cortex of a highly visual marsupial.

Primary visual cortices in many mammalian species exhibit modular and periodic orientation preference maps arranged in pinwheel-like layouts. The role of inherited traits as opposed to environmental influences in determining this organization remains unclear. Here, we characterize the cortical organization of an Australian marsupial, revealing pinwheel organization resembling that of eutherian carnivores and primates but distinctly different from the simpler salt-and-pepper arrangement of eutherian rodents and rabbits.

Optimizing captive short-beaked echidna (Tachyglossus aculeatus) fecal sample identification and hormonal analysis.

The objectives of this study were to develop a fecal marking protocol to distinguish male from female samples during the echidna breeding season and to determine if normalizing fecal progesterone metabolite data for inorganic content improves the detection of biologically relevant changes in metabolite concentrations. Over a period of 6 weeks, four echidnas were provided with green food coloring powder mixed into 20 g of their regular feed with the dose adjusted weekly by 0.05 g.