West Half, The Wren, 900 W Street and 901 W Street as these properties placed additional space into service, (iii) a $2.6 million increase related to 1770 Crystal Drive, which was placed into service in the fourth quarter of 2020, and (iv) a $1.8 million increase related to the commencement of the lease with Amazon at 2100 Crystal Drive. The increase in property rental revenue was partially offset by a $6.4 million decrease related to lower occupancy at the Universal Buildings, 2011 Crystal Drive, 2101 L Street and RTC-West.
Third-party real estate services revenue, including reimbursements, decreased by approximately $1.1 million, or 4.2%, to $25.8 million in 2021 from $27.0 million in 2020. The decrease was primarily due to a $2.0 million decrease in reimbursements revenue, a $705,000 decrease in other service revenue and a $584,000 decrease in construction management fees, partially offset by a $1.4 million increase in development fee revenue primarily related to the timing of development projects and a $736,000 increase in leasing fees.
Depreciation and amortization expense increased by approximately $245,000, or 0.4%, to $56.7 million in 2021 from $56.5 million in 2020. The increase was primarily due to (i) a $1.9 million increase related to 2345 Crystal Drive due to an increase in tenant improvements, (ii) a $1.7 million increase related to 4747 Bethesda Avenue, West Half, The Wren, 900 W Street and 901 W Street as these properties placed additional space into service, and (iii) a $924,000 increase due to 1770 Crystal Drive being placed into service. The increase in depreciation and amortization expense was partially offset by a $4.0 million decrease related to 2000 South Bell Street and 2001 South Bell Street as we commenced construction on two new buildings in 2021.
Property operating expense increased by approximately $2.6 million, or 7.0%, to $40.2 million in 2021 from $37.6 million in 2020. The increase was primarily due to (i) a $1.2 million increase related to 2451 Crystal Drive for costs incurred for construction management services provided to tenants, (ii) an $885,000 increase related to 4747 Bethesda Avenue, West Half, The Wren, 900 W Street and 901 W Street as these properties placed additional space into service, (iii) a $576,000 increase due to 1770 Crystal Drive being placed into service and (iv) $535,000 related to 2221 South Clark Street due to higher operating expenses. The increase in property operating expense was partially offset by a $1.5 million decrease related to 1901 South Bell Street due to costs incurred in 2020 for construction management services provided to tenants.
Real estate tax expense increased by approximately $905,000, or 5.2%, to $18.3 million in 2021 from $17.4 million in 2020. The increase was primarily due to a $548,000 increase related to 4747 Bethesda Avenue and The Wren as these properties placed additional space into service, and a $543,000 increase related to 5 M Street Southwest due to an increase in its applicable tax rate in 2021.
General and administrative expense: corporate and other increased by approximately $1.0 million, or 9.2%, to $12.1 million in 2021 from $11.1 million in 2020. The increase was primarily due to a decrease in capitalizable payroll costs related to development projects.
General and administrative expense: third-party real estate services decreased by approximately $2.7 million, or 9.4%, to $25.5 million in 2021 from $28.2 million in 2020. The decrease was primarily due to a decrease in reimbursable expenses.
General and administrative expense: share-based compensation related to Formation Transaction and special equity awards decreased by approximately $3.7 million, or 51.2%, to $3.5 million in 2021 from $7.1 million in 2020. The decrease was primarily due to the graded vesting of certain awards issued in prior years, which resulted in lower expense as portions of the awards vested.
Transaction and other costs of $3.0 million in 2021 primarily included $1.4 million of demolition costs related to 2000 South Bell Street and 2001 South Bell Street and $1.4 million of expenses related to completed, potential and pursued transactions. Transaction and other costs of $845,000 in 2020 consisted of $406,000 of integration and severance costs, $260,000 of expenses related to completed, potential and pursued transactions, and $179,000 of demolition costs related to 223 23rd Street and 2300 Crystal Drive.
Income from unconsolidated real estate ventures increased by approximately $21.5 million to $20.5 million for 2021 from a loss of $965,000 in 2020. The increase was primarily due to the recognition of our proportionate share of the gain from the sale of 500 L'Enfant Plaza of $23.1 million. The increase in income from unconsolidated real estate ventures was