title: Bovine Pre-gastrulation Development and the role Of Rauber's Layer

authors: van Leeuwen, Jessica

subjects: embryology

abstract: Although conception rates in cattle are estimated to be 90%, little over half of each insemination results in the birth of offspring. The majority of total combined foetal and embryonic loss is sustained between the bovine blastocyst hatching at Day 8 and the onset of gastrulation after Day 14. Post hatching, the bovine embryo develops a morphological architecture which is very different to the mouse, with a flat epiblast and the loss of the polar trophoblast, known as Rauber’s layer. In mice, the polar trophoblast is essential for the induction of gastrulation and the formation of the placenta. The pre-gastrulation layout of cattle embryos is shared by a diverse phylogeny of placental forming mammals, from rabbits to pigs, and it is therefore considered the more typical mode of mammalian embryonic development. Yet, compared to mouse embryonic development, relatively little is known about the gene expression and signalling networks required for successful gastrulation in these species, particularly cattle which are also economically important.

This thesis studied the morphological and gene expression events during Days 11-15 in cattle which coincides with the period of greatest embryonic loss. A detailed morphological staging system is presented that is supported with spatio-temporal gene expression patterns of genes known to play fundamental roles in mouse pre-gastrulation development. Novel morphological structures and processes were identified such as the formation of the cattle anterior visceral hypoblast (equivalent to the mouse AVE) and cavitation of the epiblast in preparation for epithelialisation of this tissue. Both of these processes are considered pre-requisites for the induction of gastrulation in mammals. The spatio-temporal gene expression patterns prior to gastrulation showed overall high concordance with mouse development however, processes that lead to asymmetry in the mouse involving extra-embryonic tissues have diverged and this can be related back to the different embryonic layouts and polar trophoblast fates between cattle and mice.

Functional studies were carried out in cattle embryos to investigate the relative roles of the three first cell lineages (trophoblast, epiblast and hypoblast) in contributing to embryonic loss and to investigate the possible role of Rauber’s layer in pre-gastrulation development. Over-expression of the weak pro-apoptotic factor BAD resulted in the selective loss of the epiblast between Days 7 and 13/14 of development. The trophoblast was not measurably impaired and although the hypoblast was not lost, the gene expression profile of this tissue was dramatically altered. These results indicate a gradient of sensitivity of epiblast>hypoblast>trophoblast tissue and suggest the epiblast contributes more greatly overall to embryonic loss. This result provides insights into the phenomenom of “phantom pregnancies”, which also are due to loss of the epiblast/embryo proper and are thought to occur in 12-22% of cattle pregnancies. 

The loss of Rauber’s layer is thought to occur by apoptosis and the results shown in this thesis support this idea. Over-expression of anti-apoptotic BCL2 resulted in a delayed loss of Rauber’s layer. BCL2 embryos also had an increased epiblast length and one embryo showed ectopic mesoderm formation. These results are consistent with the hypothesis that a maintained Rauber’s layer could lead to an increase in NODAL signalling. 

The findings in this thesis provide a foundational step in the establishment of the bovine embryo as a model for mammalian development. The results also demonstrate functional perturbations of the cattle embryo are experimentally feasible, and how these have revealed insights into cattle embryonic loss and the role of Rauber’s layer in development.

text: Bovine Pre-gastrulation Development and the role Of Rauber's Layer Although conception rates in cattle are estimated to be 90%, little over half of each insemination results in the birth of offspring. The majority of total combined foetal and embryonic loss is sustained between the bovine blastocyst hatching at Day 8 and the onset of gastrulation after Day 14. Post hatching, the bovine embryo develops a morphological architecture which is very different to the mouse, with a flat epiblast and the loss of the polar trophoblast, known as Rauber’s layer. In mice, the polar trophoblast is essential for the induction of gastrulation and the formation of the placenta. The pre-gastrulation layout of cattle embryos is shared by a diverse phylogeny of placental forming mammals, from rabbits to pigs, and it is therefore considered the more typical mode of mammalian embryonic development. Yet, compared to mouse embryonic development, relatively little is known about the gene expression and signalling networks required for successful gastrulation in these species, particularly cattle which are also economically important.

This thesis studied the morphological and gene expression events during Days 11-15 in cattle which coincides with the period of greatest embryonic loss. A detailed morphological staging system is presented that is supported with spatio-temporal gene expression patterns of genes known to play fundamental roles in mouse pre-gastrulation development. Novel morphological structures and processes were identified such as the formation of the cattle anterior visceral hypoblast (equivalent to the mouse AVE) and cavitation of the epiblast in preparation for epithelialisation of this tissue. Both of these processes are considered pre-requisites for the induction of gastrulation in mammals. The spatio-temporal gene expression patterns prior to gastrulation showed overall high concordance with mouse development however, processes that lead to asymmetry in the mouse involving extra-embryonic tissues have diverged and this can be related back to the different embryonic layouts and polar trophoblast fates between cattle and mice.

Functional studies were carried out in cattle embryos to investigate the relative roles of the three first cell lineages (trophoblast, epiblast and hypoblast) in contributing to embryonic loss and to investigate the possible role of Rauber’s layer in pre-gastrulation development. Over-expression of the weak pro-apoptotic factor BAD resulted in the selective loss of the epiblast between Days 7 and 13/14 of development. The trophoblast was not measurably impaired and although the hypoblast was not lost, the gene expression profile of this tissue was dramatically altered. These results indicate a gradient of sensitivity of epiblast>hypoblast>trophoblast tissue and suggest the epiblast contributes more greatly overall to embryonic loss. This result provides insights into the phenomenom of “phantom pregnancies”, which also are due to loss of the epiblast/embryo proper and are thought to occur in 12-22% of cattle pregnancies. 

The loss of Rauber’s layer is thought to occur by apoptosis and the results shown in this thesis support this idea. Over-expression of anti-apoptotic BCL2 resulted in a delayed loss of Rauber’s layer. BCL2 embryos also had an increased epiblast length and one embryo showed ectopic mesoderm formation. These results are consistent with the hypothesis that a maintained Rauber’s layer could lead to an increase in NODAL signalling. 

The findings in this thesis provide a foundational step in the establishment of the bovine embryo as a model for mammalian development. The results also demonstrate functional perturbations of the cattle embryo are experimentally feasible, and how these have revealed insights into cattle embryonic loss and the role of Rauber’s layer in development.

year: 2016

title: Curing kinetics and effects of fibre surface treatment and curing parameters on the interfacial and tensile properties of hemp/epoxy composites

authors: Islam, Mohammad Saiful

subjects: hemp fibre

abstract: The curing kinetics of neat epoxy (NE) and hemp fibre/epoxy composites was studied and assessed using two dynamic models (the Kissinger and Flynn-Wall-Ozawa Models) and an isothermal model (the Autocatalytic Model) which was generally supported by the experimental data obtained from dynamic and isothermal differential scanning calorimetry (DSC) scans. The activation energies for the curing of composites exhibited lower values compared to curing of NE which is believed to be due to higher nucleophilic activity of the amine groups of the curing agent in the presence of fibres. The highest tensile strength, σ was obtained with composites produced with an epoxy to curing agent ratio of 1:1 and the highest Young's modulus, E was obtained with an epoxy to curing agent ratio of 1:1.2. Alkali treated hemp fibre/epoxy (ATFE) composites were found to have higher σ and E values compared to those for untreated hemp fibre/epoxy (UTFE) composites which was consistent with the trend for interfacial shear strength (IFSS) values. Composites σ and E were found to be higher for a processing temperature of 70°C than for 25°C for both UTFE and ATFE composites, but were found to decrease as the curing temperature was increased further to 120°C.

text: Curing kinetics and effects of fibre surface treatment and curing parameters on the interfacial and tensile properties of hemp/epoxy composites The curing kinetics of neat epoxy (NE) and hemp fibre/epoxy composites was studied and assessed using two dynamic models (the Kissinger and Flynn-Wall-Ozawa Models) and an isothermal model (the Autocatalytic Model) which was generally supported by the experimental data obtained from dynamic and isothermal differential scanning calorimetry (DSC) scans. The activation energies for the curing of composites exhibited lower values compared to curing of NE which is believed to be due to higher nucleophilic activity of the amine groups of the curing agent in the presence of fibres. The highest tensile strength, σ was obtained with composites produced with an epoxy to curing agent ratio of 1:1 and the highest Young's modulus, E was obtained with an epoxy to curing agent ratio of 1:1.2. Alkali treated hemp fibre/epoxy (ATFE) composites were found to have higher σ and E values compared to those for untreated hemp fibre/epoxy (UTFE) composites which was consistent with the trend for interfacial shear strength (IFSS) values. Composites σ and E were found to be higher for a processing temperature of 70°C than for 25°C for both UTFE and ATFE composites, but were found to decrease as the curing temperature was increased further to 120°C.

year: 2009

title: Mainstreaming managed retreat in Aotearoa New Zealand [Policy Brief]

authors: Hanna, Christina Jane

abstract: Retreat in Aotearoa has evolved from early indigenous practices which saw relocation from harm as a viable option, to the onset of colonisation and more protection-based approaches, to more passive policy that acknowledged the option of retreat but provided little guidance or implementation support, to today, when retreat is becoming a strategic part of our national risk management framework.

text: Mainstreaming managed retreat in Aotearoa New Zealand [Policy Brief] Retreat in Aotearoa has evolved from early indigenous practices which saw relocation from harm as a viable option, to the onset of colonisation and more protection-based approaches, to more passive policy that acknowledged the option of retreat but provided little guidance or implementation support, to today, when retreat is becoming a strategic part of our national risk management framework.

year: 2023-04