A series of elegant embryo transfer experiments in the 1950s demonstrated that the uterine environment could alter vertebral patterning in inbred mouse strains. In the intervening decades, attention ...has tended to focus on the technical achievements involved and neglected the underlying biological question: how can genetically homogenous individuals have a heterogenous number of vertebrae? Here I revisit these experiments and, with the benefit of knowledge of the molecular‐level processes of vertebral patterning gained over the intervening decades, suggest a novel hypothesis for homeotic transformation of the last lumbar vertebra to the adjacent sacral type through regulation of Hox genes by sex steroids. Hox genes are involved in both axial patterning and development of male and female reproductive systems and have been shown to be sensitive to sex steroids in vitro and in vivo. Regulation of these genes by sex steroids and resulting alterations to vertebral patterning may hint at a deep evolutionary link between the ribless lumbar region of mammals and the switch from egg‐laying to embryo implantation. An appreciation of the impact of sex steroids on Hox genes may explain some puzzling aspects of human disease, and highlights the spine as a neglected target for in utero exposure to endocrine disruptors.
The uterine environment can alter vertebral patterning. Here I argue that this occurs via regulation of Hox genes by sex steroids. If sex steroids can alter vertebral patterning, then so might in utero exposure to endocrine‐disrupting chemicals (EDCs), highlighting the spine as an unappreciated target of EDCs.
Given an equal sex ratio at conception, the excess of human males at birth can only be explained by greater loss of females during pregnancy. It is proposed that the bias against females during human ...development is the result of a greater degree of genetic and metabolic “differentness” between female embryos and maternal tissues than for similarly aged males, and that successful implantation and placentation represents a threshold dichotomy, where the acceptance threshold shifts depending on maternal condition, especially stress. Right and left ovaries are not equal, and neither are the eggs and follicular fluid that they produce, and it is further hypothesized that during times of stress, the implantation threshold is shifted sufficiently to favor survival of females, most likely those originating from the right ovary, and that this, rather than simply a greater loss of males, explains at least some of the variability in the human sex ratio at birth.
Equal numbers of boys and girls are conceived, yet the sex ratio at birth is biased toward males. A greater number of girls are lost to spontaneous abortion (miscarriage), most likely because female embryos are metabolically and genetically more different to their mother.
Nonmodel rodents are widely used as subjects for both basic and applied biological research, but the genetic diversity of the study individuals is rarely quantified. University-housed colonies tend ...to be small and subject to founder effects and genetic drift; so they may be highly inbred or show substantial genetic divergence from other colonies, even those derived from the same source. Disregard for the levels of genetic diversity in an animal colony may result in a failure to replicate results if a different colony is used to repeat an experiment, as different colonies may have fixed alternative variants. Here we use high throughput sequencing to demonstrate genetic divergence in three isolated colonies of Mongolian gerbil (
) even though they were all established recently from the same source. We also show that genetic diversity in allegedly "outbred" colonies of nonmodel rodents (gerbils, hamsters, house mice, deer mice, and rats) varies considerably from nearly no segregating diversity to very high levels of polymorphism. We conclude that genetic divergence in isolated colonies may play an important role in the "replication crisis." In a more positive light, divergent rodent colonies represent an opportunity to leverage genetically distinct individuals in genetic crossing experiments. In sum, awareness of the genetic diversity of an animal colony is paramount as it allows researchers to properly replicate experiments and also to capitalize on other genetically distinct individuals to explore the genetic basis of a trait.
The identification of apparently conserved gene complements in the venom and salivary glands of a diverse set of reptiles led to the development of the Toxicofera hypothesis – the single, early ...evolution of the venom system in reptiles. However, this hypothesis is based largely on relatively small scale EST-based studies of only venom or salivary glands and toxic effects have been assigned to only some putative Toxicoferan toxins in some species. We set out to examine the distribution of these proposed venom toxin transcripts in order to investigate to what extent conservation of gene complements may reflect a bias in previous sampling efforts. Our quantitative transcriptomic analyses of venom and salivary glands and other body tissues in five species of reptile, together with the use of available RNA-Seq datasets for additional species, shows that the majority of genes used to support the establishment and expansion of the Toxicofera are in fact expressed in multiple body tissues and most likely represent general maintenance or “housekeeping” genes. The apparent conservation of gene complements across the Toxicofera therefore reflects an artefact of incomplete tissue sampling. We therefore conclude that venom has evolved multiple times in reptiles.
•Transcripts encoding proposed venom toxins are expressed in multiple body tissues.•Many hypothesised venom components are in fact housekeeping genes.•The complexity of snake venom has been overestimated by previous authors.•Venom has evolved multiple times in reptiles.
We present a genome assembly from an individual male
(the variegated flesh fly; Arthropoda; Insecta; Diptera; Sarcophagidae). The genome sequence is 718.5 megabases in span. Most of the assembly is ...scaffolded into 7 chromosomal pseudomolecules including the X and Y sex chromosomes. The mitochondrial genome has also been assembled and is 18.7 kilobases in length. Gene annotation of this assembly on Ensembl identified 16,660 protein coding genes.
We present a genome assembly from an individual male
(the Birch Marble; Arthropoda; Insecta; Lepidoptera; Tortricidae). The genome sequence is 684 megabases in span. Most of the assembly is ...scaffolded into 28 chromosomal pseudomolecules with the Z sex chromosome assembled. The mitochondrial genome has also been assembled and is 15.8 kilobases in length. Gene annotation of this assembly on Ensembl identified 21,717 protein coding genes.
We present a genome assembly from an individual male
(the bluish flesh fly; Arthropoda; Insecta; Diptera; Sarcophagidae). The genome sequence is 597 megabases in span. Most of the assembly is ...scaffolded into seven chromosomal pseudomolecules, including the assembled X and Y sex chromosomes. The mitochondrial genome has also been assembled and is 21.1 kilobases in length. Gene annotation of this assembly on Ensembl identified 16,559 protein coding genes.
We present a genome assembly from an individual male
Sarcophaga subvicina
(the lesser worm flesh fly; Arthropoda; Insecta; Diptera; Sarcophagidae). The genome sequence is 71 megabases in span. Most ...of the assembly (95.91%) is scaffolded into six chromosomal pseudomolecules, with the X sex chromosome assembled. The mitochondrial genome has also been assembled and is 16.7 kilobases in length. Gene annotation of this assembly on Ensembl identified 16,793 protein coding genes.
We present a genome assembly from an individual female
(the Six-striped Rustic; Arthropoda; Insecta; Lepidoptera; Noctuidae). The genome sequence is 638.3 megabases in span. Most of the assembly is ...scaffolded into 32 chromosomal pseudomolecules, including the W and Z sex chromosomes. The mitochondrial genome has also been assembled and is 15.36 kilobases in length. Gene annotation of this assembly on Ensembl identified 15,104 protein coding genes.
We present a genome assembly from an individual male
(the Riband Wave; Arthropoda; Insecta; Lepidoptera; Geometridae). The genome sequence is 437 megabases in span. The whole assembly is scaffolded ...into 30 chromosomal pseudomolecules, including the assembled Z sex chromosome. The mitochondrial genome has also been assembled and is 17.5 kilobases in length. Gene annotation of this assembly on Ensembl identified 10,165 protein coding genes.
PDF
